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Two samples of human breast milk. The sample on the left is the first milk produced by the mother, while the sample on the right was produced later during the same breast pumping cycle.

Breast milk (sometimes spelled as breastmilk) or mother's milk is milk produced by the mammary glands in the breasts of women. Breast milk is the primary source of nutrition for newborn infants, comprising fats, proteins, carbohydrates, and a varying composition of minerals and vitamins. Breast milk also contains substances that help protect an infant against infection and inflammation, such as symbiotic bacteria and other microorganisms and immunoglobulin A, whilst also contributing to the healthy development of the infant's immune system and gut microbiome.[1]

Use and methods of consumption

[edit]
Pumped breast milk in bottles
Breast feeding latch

The World Health Organization (WHO) and UNICEF recommend exclusive breastfeeding with breast milk for the first six months of an infant's life. This period is followed by the incorporation of nutritionally adequate and safe complementary solid foods at six months, a stage when an infant's nutrient and energy requirements start to surpass what breast milk alone can provide. Continuation of breastfeeding is recommended up to two years of age. This guidance is due to the protective benefits of breast milk, which include fewer infections such as diarrhea—a protection not afforded by formula milk.[2]

Breast milk constitutes the sole source of nutrition for exclusively breastfed newborns, supplying all necessary nutrients for infants up to six months. Beyond this age, breast milk continues to be a source of energy for children up to two years old, providing over half of a child's energy needs up to the age of one and a third of the needs between one and two years of age.[2]

Despite the capability of most newborns to latch onto the mother's breast within an hour of birth, globally, sixty percent of infants are not breastfed within this crucial first hour. Breastfeeding within the first hour of life protects the newborn from acquiring infections and reduces risk of death during the neonatal period.[3][4]

Alternatively, breast milk can be expressed using a breast pump and administered via baby bottle, cup, spoon, supplementation drip system, or nasogastric tube.[5] This method is especially beneficial for preterm babies who may initially lack the ability to suck effectively. Using cups to feed expressed breast milk and other supplements results in improved breastfeeding outcomes in terms of both duration and extent, compared with traditional bottle and tube feeding.[5][6]

For mothers unable to produce an adequate supply of breast milk, the use of pasteurized donor human breast milk is a viable option. In the absence of pasteurized donor milk, commercial formula milk is recommended as a secondary alternative.[7] However, unpasteurized breast milk from a source other than the infant's mother, particularly when shared informally, carries the risk of vertically transmitting bacteria, viruses (such as HIV), and other microorganisms from the donor to the infant, rendering it an unsafe alternative.[7][8]

Benefits

[edit]

Breastfeeding offers health benefits to mother and child even after infancy.[9] These benefits include proper heat production and adipose tissue development,[10] a 73% decreased risk of sudden infant death syndrome,[11] increased intelligence,[12] decreased likelihood of contracting middle ear infections,[13] cold and flu resistance,[14] a tiny decrease in the risk of childhood leukemia,[15] lower risk of childhood onset diabetes,[16] decreased risk of asthma and eczema,[17] decreased dental problems,[17] decreased risk of obesity later in life,[18] and a decreased risk of developing psychological disorders, including in adopted children.[19] In addition, feeding an infant breast milk is associated with lower insulin levels and higher leptin levels compared feeding an infant via powdered-formula.[20] Many of the infection-fighting and immune system related benefits are associated with human milk oligosaccharides.[21]

Breastfeeding also provides health benefits for the mother. It assists the uterus in returning to its pre-pregnancy size and reduces post-partum bleeding, through the production of oxytocin (see Production). Breastfeeding can also reduce the risk of breast cancer later in life.[22][23] Lactation may also reduce the risk for both mother and infant from both types of diabetes.[24] Lactation may protect the infant from specifically developing Type 2 diabetes, as studies have shown that bioactive ingredients in human breast milk could prevent excess weight gain during childhood via contributing to a feeling of energy and satiety. The lower risk of child-onset diabetes may be more applicable to infants who were born from diabetic mothers.[20] The reason is that while breastfeeding for at least the first six months of life minimizes the risk of type 1 diabetes from occurring in the infant, inadequate breastfeeding in an infant prenatally exposed to diabetes was associated with a higher risk of the child developing diabetes later.[20] There are arguments that breastfeeding may contribute to protective effects against the development of type 1 diabetes because the alternative of bottle-feeding may expose infants to unhygienic feeding conditions.[25]

Though it is almost universally prescribed, in some countries during the 1950s, the practice of breastfeeding went through a period where it was out of vogue and the use of infant formula was considered superior to breast milk.[26] However, it is since universally recognized that there is no commercial formula that can adequately substitute for breast milk. In addition to the appropriate amounts of carbohydrate, protein, and fat, breast milk provides vitamins, minerals, digestive enzymes,[27] and hormones.[27] Breast milk also contains antibodies and lymphocytes from the mother that may help the baby resist infections.[28] The immune function of breast milk is individualized, as the mother, through her touching and taking care of the baby, comes into contact with pathogens that colonize the baby, and, as a consequence, her body makes the appropriate antibodies and immune cells.[29]

At around four months of age, the internal iron supplies of the infant, held in the hepatic cells of the liver, are exhausted. The American Academy of Pediatrics recommends that at this time that an iron supplement should be introduced.[30] Other health organisations such as the NHS in the UK have no such recommendation.[31] Breast milk contains less iron than formula, but the iron is more bioavailable as lactoferrin, which carries more safety for mothers and children than ferrous sulphate.[32]

Both the AAP[33] and the NHS recommend vitamin D supplementation for breastfed infants.[31] Vitamin D can be synthesised by the infant via exposure to sunlight; however, many infants are deficient due to being kept indoors or living in areas with insufficient sunlight. Formula is supplemented with vitamin D for this reason.[31][33]

Production

[edit]
See also: Low milk supply

Under the influence of the hormones prolactin and oxytocin, women produce milk after childbirth to feed the baby.[34] The initial milk produced is referred to as colostrum, which is high in the immunoglobulin IgA, which coats the gastrointestinal tract. This helps to protect the newborn until its own immune system is functioning properly. It also creates a mild laxative effect, expelling meconium and helping to prevent the build-up of bilirubin (a contributory factor in jaundice[35]). Male lactation can occur; the production or administration of the hormone prolactin is necessary to induce lactation (see male lactation).

Actual inability to produce enough milk is rare, with studies showing that mothers from malnourished regions still produce amounts of milk of similar quality to that of mothers in developed countries.[36] There are many reasons a mother may not produce enough breast milk.[37] Some of the most common reasons are an improper latch (i.e., the baby does not connect efficiently with the nipple), not nursing or pumping enough to meet supply, certain medications (including estrogen-containing hormonal contraceptives), illness, and dehydration. A rarer reason is Sheehan's syndrome, also known as postpartum hypopituitarism, which is associated with prolactin deficiency and may require hormone replacement.

The amount of milk produced depends on how often the mother is nursing and/or pumping: the more the mother nurses her baby or pumps, the more milk is produced.[38][39][40] It is beneficial to nurse when the baby wants to nurse rather than on a schedule. A Cochrane review came to the conclusion that a greater volume of milk is expressed whilst listening to relaxing audio during breastfeeding, along with warming and massaging of the breast prior to and during feeding. A greater volume of milk expressed can also be attributed to instances where the mother starts pumping milk sooner, even if the infant is unable to breastfeed.[41]

Sodium concentration is higher in hand-expressed milk, when compared with the use of manual and electric pumps, and fat content is higher when the breast has been massaged, in conjunction with listening to relaxing audio. This may be important for low birthweight infants.[41] If pumping, it is helpful to have an electric, high-grade pump so that all of the milk ducts are stimulated. Galactagogues increase milk supply, although even herbal variants carry risks. Non-pharmaceutical methods should be tried first, such as pumping out the mother's breast milk supply often, warming or massaging the breast, as well as starting milk pumping earlier after the child is born if they cannot drink milk at the breast.[41][42][43][44]

Composition

[edit]
Further information: Anti inflammatory agents in breast milk, Human milk immunity, and Human milk microbiome
Human breast milk
Nutritional value per 100 mL
Energy65–78 kcal (270–330 kJ)
6.7–7.8 g
Sugars
6.7–7.8 g
3.2–4.8 g
0.8–1.4 g
Vitamins and minerals
VitaminsQuantity
%DV†
Vitamin A220 IU
Thiamine (B1)
2%
21 μg
Riboflavin (B2)
3%
35 μg
Niacin (B3)
1%
0.15 mg
Vitamin B6
–%
9–21 μg
Folate (B9)
–%
2–5 μg
Vitamin B12
4%
0.1 μg
Vitamin C
4%
4 mg
Vitamin D
0%
2 IU
Vitamin E
1%
0.2 mg
Vitamin K
0%
0.2 μg
MineralsQuantity
%DV†
Calcium
–%
20–25 mg
Copper
–%
0.00001–0.00003 mg
Iron
–%
0.03–0.07 mg
Magnesium
–%
3–3.5 mg
Manganese
–%
0.0003–0.0004 mg
Phosphorus
–%
12–14 mg
Potassium
–%
40–55 mg
Selenium
–%
1–2.5 μg
Sodium
–%
15–25 mg
Zinc
–%
0.0001–0.0003 mg
Other constituentsQuantity
Water87–88 g
†Percentages estimated using US recommendations for adults,[48] except for potassium, which is estimated based on expert recommendation from the National Academies.[49]
Source: [45][46][47]

Breast milk contains fats, proteins, carbohydrates (including lactose and human milk oligosaccharides), and a varying composition of minerals and vitamins.[50][51] The composition changes over a single feed as well as over the period of lactation.[52] Changes are particularly pronounced in marsupials.[53]

Colostrum vs breastmilk

During the first few days after delivery, the mother produces colostrum. This is a thin yellowish fluid that is the same fluid that sometimes leaks from the breasts during pregnancy. It is rich in protein and antibodies that provide passive immunity to the baby (the baby's immune system is not fully developed at birth). Colostrum also helps the newborn's digestive system to grow and function properly.[citation needed]

Colostrum will gradually change to become mature milk. In the first 3–4 days it will appear thin and watery and will taste very sweet; later, the milk will be thicker and creamier. Human milk quenches the baby's thirst and hunger and provides the proteins, sugar, minerals, and antibodies that the baby needs.

In the 1980s and 1990s, lactation professionals (De Cleats) used to make a differentiation between foremilk and hindmilk. But this differentiation causes confusion as there are not two types of milk. Instead, as a baby breastfeeds, the fat content very gradually increases, with the milk becoming fattier and fattier over time.[54]

The level of Immunoglobulin A (IgA) in breast milk remains high from day 10 until at least 7.5 months post-partum.[55]

Human milk contains 0.8–0.9% protein, 4.5% fat, 7.1% carbohydrates, and 0.2% ash (minerals).[56] Carbohydrates are mainly lactose; several lactose-based oligosaccharides (also called human milk oligosaccharides) have been identified as minor components.[57] The fat fraction contains specific triglycerides of palmitic and oleic acid (O-P-O triglycerides), and also lipids with trans bonds (see: trans fat). The lipids are vaccenic acid, and conjugated linoleic acid (CLA) accounting for up to 6% of the human milk fat.[58][59]

The principal proteins are alpha-lactalbumin, lactoferrin (apo-lactoferrin), IgA, lysozyme, and serum albumin. In an acidic environment such as the stomach, alpha-lactalbumin unfolds into a different form and binds oleic acid to form a complex called HAMLET that kills tumor cells.[citation needed] This is thought to contribute to the protection of breastfed babies against cancer.[60]

Non-protein nitrogen-containing compounds, making up 25% of the milk's nitrogen, include urea, uric acid, creatine, creatinine, amino acids, and nucleotides.[61][62] Breast milk has circadian variations; some of the nucleotides are more commonly produced during the night, others during the day.[63]

Mother's milk has been shown to supply endocannabinoids (the natural neurotransmitters that cannabis simulates) 2-arachidonoylglycerol,[64] anandamide,[65][66] oleoylethanolamide,[67] palmitoylethanolamide,[67] N-arachidonoyl glycine,[67] eicosapentaenoyl ethanolamide,[67] docosahexaenoyl ethanolamide,[67] N-palmitoleoyl-ethanolamine,[67] dihomo-γ-linolenoylethanolamine,[67] N-stearoylethanolamine,[67] prostaglandin F2alpha ethanolamides[67] and prostaglandin F2 ethanolamides,[67] Palmitic acid esters of hydroxy-stearic acids (PAHSAs).[68] They may act as an appetite stimulant, but they also regulate appetite so infants do not eat too much. That may be why formula-fed babies have a higher caloric intake than breastfed babies.[69]

Breast milk is not sterile and has its own microbiome, but contains as many as 600 different species of various bacteria, including beneficial Bifidobacterium breve, B. adolescentis, B. longum, B. bifidum, and B. dentium, which contribute to colonization of the infant gut.[70] As a result, it can be defined as a probiotic food, depending on how one defines "probiotic".[71] Breast milk also contains a variety of somatic cells and stem cells and the proportion of each cell type differs from individual to individual.[72][73] The somatic cells are mainly lactocytes and myoepithelial cells derived from the mother's mammary glands.[74] The stem cells found in human breast milk have been shown to be able to differentiate into a variety of other cells involved in the production of bodily tissues and a small proportion of these cross over the nursing infant's intestinal tract into the bloodstream to reach certain organs and transform into fully functional cells.[75] Because of its diverse population of cells and multifarious functions, researchers have argued that breast milk should be considered a living tissue.[72]

Breast milk contains a unique type of sugars, human milk oligosaccharides (HMOs), which were not present in traditional infant formula, however they are increasingly added by many manufacturers. HMOs are not digested by the infant but help to make up the intestinal flora.[76] They act as decoy receptors that block the attachment of disease causing pathogens, which may help to prevent infectious diseases.[77] They also alter immune cell responses, which may benefit the infant. As of 2015 more than a hundred different HMOs have been identified; both the number and composition vary between women and each HMO may have a distinct functionality.[78]

The breast milk of diabetic mothers has been shown to have a different composition from that of non-diabetic mothers. It may contain elevated levels of glucose and insulin and decreased polyunsaturated fatty acids. A dose-dependent effect of diabetic breast milk on increasing language delays in infants has also been noted, although doctors recommend that diabetic mothers breastfeed despite this potential risk.[79]

Women breastfeeding should consult with their physician regarding substances that can be unwittingly passed to the infant via breast milk, such as alcohol, viruses (HIV or HTLV-1), or medications.[80] Even though most infants infected with HIV contract the disease from breastfeeding, most infants that are breastfed by their HIV positive mothers never contract the disease.[81] While this paradoxical phenomenon suggests that the risk of HIV transmission between an HIV positive mother and her child via breastfeeding is small, studies have also shown that feeding infants with breast milk of HIV-positive mothers can actually have a preventative effect against HIV transmission between the mother and child.[81] This inhibitory effect against the infant contracting HIV is likely due to unspecified factors exclusively present in breast milk of HIV-positive mothers.[81]

Most women that do not breastfeed use infant formula, but breast milk donated by volunteers to human milk banks can be obtained by prescription in some countries.[82] In addition, research has shown that women who rely on infant formula could minimize the gap between the level of immunity protection and cognitive abilities a breastfed child benefits from versus the degree to which a bottle-fed child benefits from them.[83] This can be done by supplementing formula-fed infants with bovine milk fat globule membranes (MFGM) meant to mimic the positive effects of the MFGMs which are present in human breast milk.[84]

Storage of expressed breast milk

[edit]
Bottle of pumped breast milk

Expressed breast milk can be stored. Lipase may cause thawed milk to taste soapy or rancid due to milk fat breakdown. It is still safe to use, and most babies will drink it. Scalding it will prevent rancid taste at the expense of antibodies.[85] It should be stored with airtight seals. Some plastic bags are designed for storage periods of less than 72 hours. Others can be used for up to 12 months if frozen. This table describes safe storage time limits.[86]

Place of storage Temperature Maximum storage time
In a room 25 °C 77 °F Six to eight hours
Insulated thermal bag with ice packs Up to 24 hours
In a refrigerator 4 °C 39 °F Up to five days
Freezer compartment inside a refrigerator −15 °C 5 °F Two weeks
A combined refrigerator and freezer with separate doors −18 °C 0 °F Three to six months
Chest or upright manual defrost deep freezer −20 °C −4 °F Six to twelve months

Comparison to other milks

[edit]

All mammalian species produce milk, but the composition of milk for each species varies widely and other kinds of milk are often very different from human breast milk. As a rule, the milk of mammals that nurse frequently (including human babies) is less rich, or more watery, than the milk of mammals whose young nurse less often. Human milk is noticeably thinner and sweeter than cow's milk.

Whole cow's milk contains too little iron, retinol, vitamin E, vitamin C, vitamin D, unsaturated fats or essential fatty acids for human babies.[87][88][89][90] Whole cow's milk also contains too much protein, sodium, potassium, phosphorus and chloride which may put a strain on an infant's immature kidneys. In addition, the proteins, fats and calcium in whole cow's milk are more difficult for an infant to digest and absorb than the ones in breast milk.[88][91][92]

The composition of marsupial and monotreme milk contains essential nutrients, growth factors and immunological properties to support the development of joeys and puggles.[53]

Comparing milks (per cup [1cup=246g] in SI units of measurement)[93][94]
Nutrient Human milk Cow milk (3.25% fat) Goat milk
Calories (Kcal) 172 146 168
Water (g) 215 215 212
Protein (g) 2.5 7.9 8.7
Fat (g) 10.8 7.9 10.1
Saturated fat (g) 4.9 4.6 6.5
Monounsaturated fat (g) 4.1 2.0 2.7
Polyunsaturated fat (g) 1.2 0.5 0.4
Omega-3 fatty acids (mg) 128 183 97.6
Omega-6 fatty acids (mg) 920 293 266
Cholesterol (mg) 34.4 24.4 26.8
Carbohydrate (g) 17.0 11.0 10.9
Sugars (g) 17.0 11.0 10.9
Vitamin A (IU) 522 249 483
Vitamin C (mg) 12.3 0 3.2
Vitamin D (IU) * 9.8 97.6 29.3
Vitamin E (mg) 0.2 0.1 0.2
Vitamin K (mcg) 0.7 0.5 0.7
Thiamin (mg) 0.0 0.1 0.1
Riboflavin (mg) 0.1 0.4 0.3
Niacin (mg) 0.4 0.3 0.7
Vitamin B6 (mg) 0.0 0.1 0.1
Folate (mcg) 12 12 2
Vitamin B12 (mcg) 0.1 1.1 0.2
Pantothenic acid (mg) 0.5 0.9 0.8
Choline (mg) 39.4 34.9 39.0
Calcium (mg) 79 276 327
Iron (mg) 0.07 0.07 0.12
Magnesium (mg) 7.4 24.4 34.2
Phosphorus (mg) 34.4 222 271
Potassium (mg) 125 349 498
Sodium (mg) 42 98 122
Zinc (mg) 0.4 1.0 0.7
Copper (mg) 0.1 0.0 0.1
Manganese (mg) 0.1 0.0 0.0
Selenium (mcg) 4.4 9.0 3.4

* Note: Milk is generally fortified with vitamin D in the U.S. and Canada. Non-fortified milk contains only 2 IU per 3.5 oz.

Effects of medications and other substances on milk content

[edit]
Main article: Breastfeeding and medications
Further information: Breast milk-mediated drug delivery

Almost all medicines, or drugs, pass into breastmilk in small amounts by a concentration gradient.[95] The amount of the drug bound by maternal plasma proteins, the size of the drug molecule, the pH and/or pKa of the drug, and the lipophilicity of the drug all determine whether and how much of the drug will pass into breastmilk.[96] Medications that are mostly non-protein bound, low in molecular weight, and highly lipid-soluble are more likely to enter the breast milk in larger quantities.[97] Some drugs have no effect on the baby and can be used whilst breastfeeding, while other medications may be dangerous and harmful to the infant.[98][97]

Some medications considered generally safe for use by a breastfeeding mother, with a doctor's or pharmacist's advice, include simple analgesics or pain killers such as paracetamol/acetaminophen,[99] anti-hypertensives such as the ACE-inhibitors enalapril and captopril, anti-depressants of the SSRI and SNRI classes, and medications for gastroesophageal reflux such as omeprazole and ranitidine.[100]

Conversely, there are medications that are known to be toxic to the baby and thus should not be used in breastfeeding mothers, such as chemotherapeutic agents which are cytotoxic like cyclosporine,[101] immunosuppressants like methotrexate,[101] amiodarone, or lithium.[97][96]

Furthermore, drugs of abuse, such as cocaine, amphetamines, heroin, and marijuana cause adverse effects on the infant during breastfeeding. Adverse effects include seizures, tremors, restlessness, and diarrhea.[101]

To reduce infant exposure to medications used by the mother, use topical therapy or avoid taking the medication during breastfeeding times when possible.[95]

Hormonal products and combined oral contraceptives should be avoided during the early postpartum period as they can interfere with lactation.[100]

There are some medications that may stimulate the production of breast milk. These medications may be beneficial in cases where women with hypothyroidism may be unable to produce milk.[102][103] A Cochrane review looked at the drug domperidone (10 mg three times per day) with results showing a significant increase in volume of milk produced over a period of one to two weeks.[104] However, another review concluded little evidence that use of domperidone and metoclopramide to enhance milk supply works. Instead, non-pharmacological approaches such as support and more frequent breastfeeding may be more efficacious.[96]

Finally, there are other substances besides medications that may appear in breast milk. Alcohol use during pregnancy carries a significant risk of serious birth defects, but consuming alcohol after the birth of the infant is considered safe.[105] High caffeine intake by breastfeeding mothers may cause their infants to become irritable or have trouble sleeping.[96] A meta-analysis has shown that breastfeeding mothers who smoke expose their infants to nicotine, which may cause respiratory illnesses, including otitis media in the nursing infant.[101]

Market

[edit]
Main article: human milk bank

There is a commercial market for human breast milk, both in the form of a wet nurse service and as a milk product.

As a product, breast milk is exchanged by human milk banks, as well as directly between milk donors and customers as mediated by websites on the internet. Human milk banks generally have standardized measures for screening donors and storing the milk, sometimes even offering pasteurization, while milk donors on websites vary in regard to these measures. A study in 2013 came to the conclusion that 74% of breast milk samples from providers found from websites were colonized with gram-negative bacteria or had more than 10,000 colony-forming units/mL of aerobic bacteria.[106] Bacterial growth happens during transit.[106] According to the FDA, bad bacteria in food at room temperature can double every 20 minutes.[107]

Human milk is considered to be healthier than cow's milk and infant formula when it comes to feeding an infant in the first six months of life, but only under extreme situations do international health organizations support feeding an infant breast milk from a healthy wet nurse rather than that of its biological mother.[108] One reason is that the unregulated breast milk market is fraught with risks, such as drugs of abuse and prescription medications being present in donated breast milk.[108] The transmission of these substances through breast milk can do more harm than good when it comes to the health outcomes of the infant recipient.[108]

Fraud

[edit]

In the United States, the online marketplace for breast milk is largely unregulated and the high premium has encouraged food fraud.[109][110] Human breast milk may be diluted with other liquids to increase volume including cow's milk, soy milk, and water, thus undermining its health benefits.[109][111]

A 2015 CBS article cites an editorial led by Dr. Sarah Steele in the Journal of the Royal Society of Medicine, in which they say that "health claims do not stand up clinically and that raw human milk purchased online poses many health risks." CBS found a study from the Center for Biobehavioral Health at Nationwide Children's Hospital in Columbus that "found that 11 out of 102 breast milk samples purchased online were actually blended with cow's milk." The article also explains that milk purchased online may be improperly sanitized or stored, so it may contain food-borne illness and infectious diseases such as hepatitis and HIV.[112]

Consumption by adults

[edit]

Restaurants and recipes

[edit]

A minority of people, including restaurateurs Hans Lochen of Switzerland and Daniel Angerer of Austria, who operate a restaurant in New York City, have used human breast milk, or at least advocated its use, as a substitute for cow's milk in dairy products and food recipes.[113][114] An icecreamist in London's Covent Garden, The Licktators, started selling an ice cream named Baby Gaga in February 2011. Each serving cost £14. All the milk was donated by a Mrs Hiley who earned £15 for every 10 ounces and called it a "great recession beater".[115] The ice cream sold out on its first day. Despite the success of the new flavour, the Westminster Council officers removed the product from the menu to make sure that it was, as they said, "fit for human consumption."[116] Tammy Frissell-Deppe, a family counsellor specialized in attachment parenting, published a book, titled A Breastfeeding Mother's Secret Recipes, providing a lengthy compilation of detailed food and beverage recipes containing human breast milk.[117] Human breast milk is not produced or distributed industrially or commercially, because the use of human breast milk as an adult food is considered unusual to the majority of cultures around the world, and most disapprove of such a practice.[118]

In Costa Rica, there have been trials to produce human cheese, and custard from human milk, as an alternative to weaning.[119]

Bodybuilders

[edit]

While there is no scientific evidence that shows that breast milk is advantageous for adults, according to several 2015 news sources, breast milk is being used by bodybuilders for its nutritional value. In a February 2015 ABC News article, one former competitive body builder said, "It isn't common, but I've known people who have done this. It's certainly talked about quite a bit on the bodybuilding forums on the Internet." Calling bodybuilders "a strange breed of individuals", he said, "Even if this type of thing is completely unsupported by research, they're prone to gym lore and willing to give it a shot if there is any potential effect." At the time the article was written, in the U.S., the price of breast milk procured from milk banks that pasteurize the milk, and have expensive quality and safety controls, was about $10 per US fluid ounce ($0.34/ml), and the price in the alternative market online, bought directly from mothers, ranges from $1–$4 per US fluid ounce ($0.03–$0.14/ml), compared to cow's milk at about $3.44 per US gallon ($0.0269/US fl oz; $0.0009/ml).[120][121]

Erotic lactation

[edit]
Main article: Erotic lactation

For sexual purposes, some couples have decided to induce lactation outside a pregnancy through a practice called "Erotic lactation".

Breast milk contamination

[edit]

Breast milk is oftentimes used as an environmental bioindicator given its ability to accumulate certain chemicals, including organochlorine pesticides.[122] Research has found that certain organic contaminants such as PCBs, organochlorine pesticides, PCDDs, PBDEs, and DDT can contaminate breastmilk.[123] According to research done in 2002, the levels of the organochlorine pesticides, PCBs, and dioxins have declined in breast milk in countries where these chemicals have been banned or otherwise regulated, while levels of PBDEs are rising.[123]

Pesticide contamination in breastmilk

[edit]

Pesticides and other toxic substances bioaccumulate; i.e., creatures higher up the food chain will store more of them in their body fat. This is an issue in particular for the Inuit, whose traditional diet is predominantly meat. Studies are looking at the effects of polychlorinated biphenyls and persistent organic pollutants in the body; the breast milk of Inuit mothers is extraordinarily high in toxic compounds.[124]

The CDC has provided some resources for breastfeeding mothers to reference for safe medication use, including LactMed, Mother to Baby, and The InfantRisk Center.[125]

Contamination effects of organochlorine pesticides on infants

[edit]

When a mother is exposed to organochlorine pesticides (OCP's), her infant can be exposed to these OCP's through breast milk intake. This result is supported by a study done in India, which revealed that in each lactation period there is a loss of OCPs from the mother's body involved in the nursing of their children. A longitudinal study was conducted to assess pesticide residues in human breast milk samples and evaluate the risk-exposure of infants to these pesticides from consumption of mother's milk in Ethiopia. The estimated daily intake (EDI) of infants in the present study was above provisional tolerable daily intake (PTDI) during the first month of breastfeeding which indicates that there is a health risk for infants consuming breast milk at an early stage of breastfeeding in the study areas. Based on these studies, the exposure of women during pregnancy to these OCPs may lead to various health problems for fetus such as low birth weight, disturbance of thyroid hormone, and neurodevelopmental delay.[126]

See also

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References

[edit]

Further reading

[edit]
[edit]
Revisions and contributorsEdit on WikipediaRead on Wikipedia

Breast milk

View on Grokipedia
from Grokipedia
Breast milk is the nutrient-dense fluid secreted by the mammary glands of lactating females, optimized evolutionarily to supply infants with essential macronutrients, bioactive compounds, and immunological factors for growth, development, and disease resistance. Composed of approximately 87% , with the remainder primarily carbohydrates (around 7%, mainly ), lipids (3-5%), and proteins (0.8-1.2%), its composition dynamically adjusts to the infant's age and needs, providing complete caloric support without supplementation in the early months. Production initiates postpartum with , a viscous, yellowish precursor high in secretory IgA antibodies, leukocytes, and laxative properties to clear , which transitions over 2-14 days into mature milk—thinner, whiter, and volumetrically abundant, with foremilk (lactose-rich for quenching thirst) yielding to hindmilk (fat-rich for ). This phased adaptation ensures initial immune priming followed by sustained nourishment, with colostrum's protein content roughly double that of mature milk. Beyond , breast milk's immunological arsenal—including oligosaccharides that foster beneficial , cytokines modulating inflammation, and maternal antibodies targeting pathogens—empirically lowers infant risks of severe infections, (by up to 50% in preterm cases), , and later-onset conditions like and , outperforming in randomized and observational data despite variables like socioeconomic factors. Variability arises from maternal diet, , and , influencing profiles and micronutrients, yet its causal protective effects persist across studies prioritizing biological mechanisms over idealized promotion.

Biological Foundations

Evolutionary Role and Natural Function

Lactation emerged in synapsid reptiles approximately 310 million years ago during the Pennsylvanian period, initially as glandular skin secretions that moistened eggs and provided protection, evolving into nutrient-rich by the period around 170 million years ago as developed in early mammals. Mammary glands derived from apocrine-like glands associated with follicles, enabling the secretion of complex fluids containing micelles for calcium and delivery, sugars for energy, and immune factors. This transition displaced yolk-based nutrition, allowing mammalian offspring to rely on post-hatching or post-birth provisioning, a defining trait that facilitated endothermy and rapid somatic growth in small-bodied mammaliaforms by the late Triassic around 210 million years ago. The natural function of breast milk centers on serving as the primary, complete nutritional source for mammalian neonates during a period of total dependence, delivering , macronutrients, vitamins, minerals, and bioactive compounds tailored to species-specific developmental needs. In mammals, milk composition dynamically adjusts to support hydration in arid environments or high-energy demands for , while incorporating antibodies and to bolster infant immunity against pathogens before the immune system matures. This provisioning enables offspring survival without independent foraging, prioritizing maternal energy transfer during lactation's high metabolic cost, which can exceed twice the non-lactating basal rate. Evolutionarily, lactation conferred advantages by buffering offspring against environmental variability, as maternal fat stores convert unreliable food supplies into consistent output, enhancing viability in fluctuating ecosystems—a mechanism observed across mammals and particularly adaptive for humans with prolonged infancy. In humans, 's elevated content, including long-chain polyunsaturated fatty acids like DHA, supports post-natal expansion in altricial young, aligning with encephalization trends where infants are born neurologically immature to accommodate large cranial sizes during birth. Relative to other , human emphasizes oligosaccharides for establishment, indirectly aiding by fostering immune essential for neural growth. These adaptations maximized by extending , with conflicts reflecting optimal maternal strategies to balance current and future offspring.

Physiological Processes of Lactation

Lactation encompasses the synthesis and secretion of by mammary epithelial cells within the alveoli of the breast, a process that begins during and is maintained postpartum through hormonal and autocrine mechanisms. components are derived primarily from plasma precursors taken up by alveolar cells, with synthesis involving the production of , caseins, proteins, and via and secretion pathways. The mammary gland's secretory capacity develops through mammogenesis, which proliferates lobuloalveolar structures during and expands significantly in under , , and influence, achieving lobule type 3 maturity by early . Lactogenesis proceeds in distinct stages: stage I, or secretory differentiation, initiates in the second trimester around week 16 of , rendering the gland competent for milk secretion with initial production expressible by late , driven by rising and placental lactogen. Stage II, secretory activation, commences 2-3 days postpartum following progesterone withdrawal after placental expulsion, marked by abrupt increases in volume, synthesis, and closure of epithelial tight junctions, often delayed in primiparous women or cesarean deliveries. Galactopoiesis, the ongoing maintenance phase, sustains production at approximately 800 mL per day, regulated by frequent removal every 2-3 hours to counteract inhibitory signals. Prolactin, secreted by the , binds to receptors on alveolar epithelial cells to stimulate transcription of milk-specific genes, with levels surging in response to nipple suckling via neural reflexes, peaking 30 minutes post-feed to prime subsequent synthesis. Oxytocin, from the , facilitates milk ejection by contracting myoepithelial cells surrounding alveoli, propelling milk into ducts—a reflex triggered by suckling or anticipatory cues, essential for efficient transfer despite potential inhibition by stress-induced catecholamines. Autocrine regulation via the feedback inhibitor of (FIL), a synthesized in mammary cells, provides local control by reversibly inhibiting secretion in a concentration-dependent manner when accumulates, acting on trafficking and signaling without altering cell number long-term. This demand-driven dynamic ensures supply matches removal frequency, as incomplete drainage elevates FIL locally per gland, reducing output until suckling resumes, independent of systemic hormones alone.

Composition and Variations

Macronutrients and Micronutrients

Human breast milk's macronutrient composition primarily consists of carbohydrates, lipids, and proteins, which together provide approximately 60-70 kcal per 100 mL in mature milk, with carbohydrates and lipids supplying the majority of energy (around 45% and 44%, respectively). The energy density remains relatively stable during exclusive breastfeeding in the first 6 months and is not increased by exclusivity itself. Carbohydrates are predominantly at 6.9-7.2 g/100 mL, which remains relatively stable throughout and supports infant development. , averaging approximately 4.2 g/100 mL, varying widely from 1.8-8.9 g/100 mL due to factors like maternal diet, stage of feeding (foremilk vs. hindmilk), degree of breast emptying (higher fat when breasts are emptier), maternal BMI, body composition, infant sex, and lactation stage, include medium-chain fatty acids and essential polyunsaturated fats such as (DHA), contributing 40-50% of caloric intake at 9 kcal/g. Frequent nursing, common in exclusive breastfeeding, promotes more complete breast emptying and thus higher fat intake by the infant per feed, but does not alter the overall energy density of the milk produced. Proteins total 0.8-1.4 g/100 mL, decreasing from levels, with predominating over in a of about 60:40, aiding digestibility.
MacronutrientAverage Concentration (g/100 mL, mature milk)Key Notes
Carbohydrates ()6.9-7.2Stable; primary energy source for development.
Lipids ()3.5-4.0Highly variable; includes and essential fatty acids.
Proteins0.8-1.2Bioavailable; whey: ~60:40.
Micronutrients in breast milk include vitamins and minerals at concentrations tailored to infant needs, though often marginal for some (e.g., vitamin D, requiring supplementation). Vitamin A averages 50-60 μg/100 mL, supporting vision and immunity, while B vitamins (e.g., B12 at 0.3-0.5 μg/100 mL) vary with maternal status. Vitamin C ranges 4-5 mg/100 mL, and vitamin D is low at 0.4-4 μg/L without maternal supplementation of 1,000-6,400 IU/day, which can elevate levels. Vitamin E (tocopherol) is about 0.3-0.5 mg/100 mL, acting as an antioxidant. Minerals such as calcium (25-35 mg/100 mL) and phosphorus support bone growth, while iron (0.03-0.1 mg/100 mL) is highly bioavailable despite low concentration; zinc (0.1-0.3 mg/100 mL) and copper (0.04-0.2 mg/100 mL) peak in colostrum and decline. Sodium (15 mg/100 mL) and potassium (50 mg/100 mL) maintain electrolyte balance. These levels generally remain consistent from 1-6 months postpartum but can be influenced by maternal nutrition, with supplementation showing variable efficacy (e.g., for iodine or selenium).

Bioactive Components and Immunological Factors

Human breast milk contains a diverse array of bioactive components, including growth factors, enzymes, hormones, and oligosaccharides, which exert physiological effects on development, , and microbial beyond basic . These components originate from mammary epithelial cells, immune cells, or maternal plasma, and their concentrations vary dynamically with stage and maternal factors. Immunological factors form a critical subset, conferring through neutralization and immune modulation without eliciting in the recipient . Secretory immunoglobulin A (sIgA) predominates among antibodies in breast milk, comprising over 90% of total immunoglobulins and produced locally by mammary plasma cells derived from , enabling antigen-specific responses to maternal exposures. sIgA coats the infant's intestinal mucosa, blocking microbial adhesion and toxin binding while promoting a balanced ; levels peak in at approximately 10-15 g/L and decline to 1-2 g/L in mature milk, correlating positively with prolonged duration. This non-inflammatory mechanism contrasts with serum IgG, reducing risks of excessive immune activation; experimental models demonstrate sIgA's role in limiting segmented filamentous bacteria colonization and mitigating Th17-driven responses linked to allergies.01186-0) Leukocytes, including macrophages (up to 50% of total cells), neutrophils, lymphocytes, and dendritic cells, constitute 0.5-2% of milk's cellular fraction and actively transfer maternal immune memory via and signaling; their numbers decrease from (10^6 cells/mL) to mature milk but respond to signals, as evidenced by reduced CD45+ counts during neonatal illness. such as interleukin-6 (IL-6), tumor necrosis factor-alpha (TNF-α), and interferon-gamma (IFN-γ) occur in trace amounts (pg/mL range), primarily proinflammatory yet diminishing post-, supporting mucosal rather than overt ; maternal or geographic factors modulate their profiles. Antimicrobial proteins like (1-7 g/L in , decreasing thereafter) bind iron to starve pathogens and exhibit bactericidal activity, while hydrolyzes bacterial cell walls; these synergize with human milk oligosaccharides (HMOs) to shape selectively favoring Bifidobacteria. Growth factors, including (EGF) at 50-100 ng/mL—over 500-fold higher than many peers—promote epithelial maturation and gut barrier integrity, with transforming growth factor-β (TGF-β) and insulin-like growth factor-1 (IGF-1) sustaining cellular proliferation; concentrations stabilize after early but associate with infant weight trajectories. Digestive enzymes such as salt-stimulated (facilitating 70-90% of hydrolysis in the gut due to immature pancreatic function) and (supplementing neonatal starch breakdown) enhance nutrient bioavailability, with activity persisting in stored milk to aid preterm digestion. Hormones like and , derived from maternal , influence appetite regulation and adiposity, though evidence links milk inversely to offspring BMI without causal consensus. These elements collectively underscore breast milk's adaptive, living composition, though quantification challenges persist due to methodological variability in assays.

Temporal and Individual Variations

Breast milk composition undergoes significant temporal changes across stages, adapting to neonatal needs. , secreted from birth to approximately day 5 postpartum, features elevated protein levels (around 2.5 g/dL) and immunoglobulins, with lower fat (about 2.5 g/dL) and (5-6 g/dL) compared to later milk. Transitional milk follows from days 5 to 14, with increasing fat and content as volume rises, bridging to mature milk by week 2-4, which stabilizes at roughly 1.0-1.2 g/dL protein, 3.5-4.0 g/dL fat, and 7.0 g/dL . These shifts reflect physiological adjustments in function, prioritizing immune support initially before caloric density. Intra-feed variations occur as fat concentration rises progressively during a single expression or session. Foremilk, the initial milk released, is thinner with lower (typically 1-2 g/dL) and higher , providing hydration and carbohydrates, while hindmilk, obtained later, is creamier with higher (up to 6-8 g/dL or more), delivering denser calories essential for growth. This gradient results from accumulation in alveolar cells, released under oxytocin-driven contractions, with fat globule size and content increasing as empties. Diurnal fluctuations also exist, with slightly higher and bioactive factors at night, influenced by hormonal cycles. Sensory properties of breast milk, particularly taste, also reflect these temporal and intra-feed dynamics as well as individual differences. Human breast milk is generally described as sweet, milder, and thinner than cow's milk, often resembling sweetened almond milk or lightly sweetened cow's milk due to its high lactose content. The taste varies with maternal diet (e.g., garlic or spices can impart distinct flavors), lactation stage (colostrum is less sweet than mature milk), time of day, and within a feeding session (foremilk more watery, hindmilk creamier). Individual variations in milk composition span wide ranges even among healthy mothers, with protein fluctuating 0.6-1.4 g/dL, fat 1.8-8.9 g/dL, and lactose 6.4-7.6 g/dL across samples. Maternal genetics play a key role, accounting for up to 20-30% of variance in macronutrients and oligosaccharides, interacting with physiological factors like parity (multiparae often have lower protein) and body mass index (higher BMI linked to increased fat). Dietary intake affects fatty acid profiles, such as elevated omega-3 from fish consumption, while health status, including infections, can transiently boost immunological components. Geographic and lifestyle differences further modulate microbiota and micronutrients, underscoring milk's personalized nature beyond averages.30049-6)

Production Dynamics

Hormonal Regulation

The development of mammary glands for begins during under the influence of , which promotes ductal elongation and branching, while progesterone drives alveolar bud formation and lobuloalveolar growth. During , rising levels of , progesterone, and placental hormones such as further expand alveolar structures and initiate synthesis around week 16, though full milk secretion is suppressed by high progesterone concentrations from the . levels elevate progressively in to support tissue differentiation via JAK/STAT5 signaling pathways, but progesterone blocks secretory activation until parturition. Lactogenesis stage II, marked by the onset of copious production, is triggered postpartum by the abrupt withdrawal of progesterone following placental expulsion, typically within 24-72 hours, alongside surges in , , and insulin. This hormonal shift enables alveolar epithelial cells to transition to active secretion, with delays observed in cases of retained placental fragments or cesarean deliveries due to prolonged progesterone exposure. decline similarly removes inhibition, allowing to dominate milk protein and synthesis. Prolactin, secreted by lactotroph cells in the , is the primary for synthesis, acting directly on mammary alveolar cells to upregulate genes for , , and fat production. Nipple stimulation from suckling activates neural afferents to the , inhibiting (a release inhibitor) and reflexively increasing surges, which peak approximately 30 minutes into a feed to prepare for the subsequent session. Sustained responsiveness depends on frequent removal, as accumulation leads to local feedback inhibition. Oxytocin, released from the , governs milk ejection through the let-down reflex, where suckling or sensory cues like hearing an infant's cry stimulate paraventricular and supraoptic nuclei to release the hormone, contracting myoepithelial cells surrounding alveoli and ducts to propel milk toward the . This pulsatile release occurs within seconds of and facilitates efficient transfer, with multiple let-downs possible per feed; disruptions from stress, , or can inhibit it by elevating catecholamines. Oxytocin also supports maternal-infant and postpartum uterine involution. Lactation maintenance operates via an autocrine-paracrine mechanism involving a feedback inhibitor of (FIL), a protein in that accumulates in distended alveoli, signaling reduced synthesis when is unmet; regular suckling evacuates FIL, restoring production in a supply- equilibrium primarily driven by surges rather than basal levels. Metabolic hormones like glucocorticoids enhance secretory activation, while disruptions such as hypothalamic-pituitary dysfunction or agonists (e.g., certain antipsychotics) can suppress and impair supply.

Influencing Factors and Supply Challenges

Breast milk production varies significantly depending on the mother's physiology, the baby's demand, breastfeeding exclusivity, and duration. Once established (typically after the first few weeks), average daily production is approximately 700-900 mL, based on infant intake studies. Specific averages include 624 mL/day at 1 month, 735 mL/day at 3 months, and 593 mL/day at 12 months. This equates to roughly 255-330 liters per year if sustained daily throughout the year, though actual annual totals are often lower due to weaning, introduction of solids, and natural decline in supply over time. Breast milk supply is primarily regulated by an autocrine mechanism, where frequent and effective milk removal by the infant stimulates production. Delays in breastfeeding initiation, such as those caused by maternal-infant separation due to medical complications, can hinder secretory activation and lead to lower volumes during the critical early phase. Poor latch or suckling efficiency, often due to infant conditions like ankyloglossia or cleft palate, reduces milk removal and subsequently diminishes supply. Maternal health conditions significantly influence supply, with endocrine disorders such as , (PCOS), and retained placental fragments implicated in up to 5-10% of true primary lactation insufficiency cases. (BMI >30 kg/m²) pre-pregnancy correlates with delayed lactogenesis and reduced response, while and impair glandular function and milk ejection. Breast surgeries, including reductions or augmentations, may damage ducts or nerves, contributing to glandular in rare instances (prevalence <1%). Exogenous factors like hormonal contraceptives containing estrogen or progesterone can suppress and supply if introduced before full establishment, typically within the first six weeks. Smoking and alcohol consumption dose-dependently reduce volume by interfering with oxytocin release and mammary gland development. Psychosocial stress elevates cortisol, which inhibits oxytocin-mediated milk ejection and may lower overall production through reduced breastfeeding frequency; studies show stressed mothers exhibit higher milk cortisol levels and shorter durations of exclusivity. Maternal fatigue and sleep deprivation exacerbate this by disrupting hormonal rhythms, though evidence indicates recovery with rest and support. Nutritional intake has minimal direct impact on milk volume in adequately nourished women, with systematic reviews finding no consistent correlation between maternal energy or fluid intake and output beyond basic requirements (additional 500 kcal/day and 2-3 L fluids). Deficiencies in well-fed populations rarely cause low supply, though severe undernutrition (e.g., <1800 kcal/day) can reduce volume by 10-20%; supplementation primarily affects composition rather than quantity. Supply challenges often stem from perceived rather than actual insufficiency, cited by 40-50% of mothers ceasing exclusive breastfeeding before six months, despite adequate infant growth in most cases. True low supply (e.g., <500 mL/day) affects <5% of women without pathology and is diagnosed via test-weighing or growth monitoring, not subjective symptoms like soft breasts. Management prioritizes optimizing removal through frequent feeds or pumping (8-12 times daily), addressing modifiable factors, and ruling out medical causes before resorting to galactagogues, whose efficacy (e.g., domperidone increasing volume by 50-100 mL) remains limited by small trials and side effects. Oversupply, conversely, arises from overproduction due to excessive pumping or incomplete drainage, leading to engorgement and mastitis risk.

Infant Health Outcomes

Evidence-Based Protective Effects

Breast milk confers several protective effects against infant morbidity and mortality, primarily through its immunological components such as secretory IgA, lactoferrin, and oligosaccharides that modulate gut microbiota and barrier function. Exclusive breastfeeding for at least six months reduces the incidence of moderate-to-severe respiratory tract infections (including RSV, pneumonia, bronchitis, and influenza) by approximately 50% and gastrointestinal infections (such as rotavirus diarrhea and bacterial causes like E. coli) by 64%, as evidenced by dose-response associations in large cohort studies adjusting for confounders like socioeconomic status. These effects extend to ear infections (otitis media) and other mucosal infections, attributed to direct pathogen neutralization and enhanced mucosal immunity, with meta-analyses confirming causality beyond observational biases. Breastfeeding also lowers the risk of sudden infant death syndrome (SIDS), with any breastfeeding associated with a 35% reduction in odds, and exclusive breastfeeding yielding up to a 50% decrease after two months' duration in population-based analyses. This protection persists after controlling for sleep position, bedsharing, and maternal smoking, likely due to arousal responses facilitated by milk's hormonal factors like leptin and ghrelin. For allergies, prolonged breastfeeding beyond six months correlates with lower rates of severe atopic dermatitis (odds ratio 0.68) and food allergies, supported by systematic reviews of immunological modulation via anti-inflammatory cytokines. In terms of long-term outcomes, breastfeeding demonstrates a modest but consistent inverse association with childhood obesity, with meta-analyses of over 100 studies reporting a 13-26% risk reduction for ever-breastfed versus formula-fed children, independent of maternal BMI and duration effects. Cognitive benefits include a 2.66-point IQ advantage in normal-birth-weight infants, as per meta-analysis of randomized and observational data adjusting for maternal intelligence, though genetic factors like FADS2 variants may moderate this to up to 6-8 points in subsets. Evidence for reduced type 1 diabetes risk is suggestive, with each additional month of exclusive breastfeeding linked to an 17% lower odds in case-control studies, but large cohorts indicate benefits primarily from initiation rather than prolongation. These protections are strongest in low-resource settings where formula hygiene risks amplify contrasts, though high-quality formula mitigates some gaps in developed contexts.

Limitations and Potential Risks

Breast milk can transmit certain infectious agents from mother to infant, posing risks particularly in cases of maternal infection. Human immunodeficiency virus (HIV) is efficiently transmitted via breastfeeding, with the CDC recommending against it for HIV-positive mothers in high-resource settings where safe alternatives exist, as the risk of postnatal transmission can reach 10-20% without antiretroviral therapy. Human T-cell lymphotropic virus type 1 (HTLV-1) also transmits through breast milk, with seroconversion rates up to 20% in exposed infants, leading to recommendations for formula feeding among carrier mothers. Cytomegalovirus (CMV) transmission occurs in up to 50% of seropositive mothers to their infants, and in preterm neonates, it is associated with severe outcomes like sepsis-like syndrome, hearing loss, and neurodevelopmental delays, prompting some experts to advise against fresh milk use in neonatal intensive care units. Bacterial contamination of expressed milk, often from improper handling, has caused outbreaks of gram-negative infections in vulnerable infants. Food proteins ingested by the mother can pass into breast milk, triggering allergic or sensitivity reactions in predisposed infants. Approximately 2-3% of exclusively breastfed infants exhibit digestive intolerance to maternal dietary proteins, such as cow's milk, manifesting as colic, reflux, diarrhea, or blood-streaked stools due to conditions like food protein-induced enterocolitis syndrome. Eczema, wheezing, and vomiting have been linked to allergens like eggs, soy, or in milk, with symptoms resolving upon maternal elimination diets in sensitized cases, though true IgE-mediated allergies to breast milk itself remain rare. Environmental contaminants bioaccumulate in breast milk, potentially exposing infants to toxins at higher concentrations than in formula. Persistent organic pollutants (POPs), per- and polyfluoroalkyl substances (PFAS), and heavy metals like mercury and lead have been detected in milk samples globally, with perinatal exposure linked to altered infant gut microbiota, endocrine disruption, oxidative stress, and increased risks of neurodevelopmental issues or immune dysregulation. For instance, PFAS levels in milk correlate with reduced infant vaccine responses and thyroid hormone perturbations, though long-term causal impacts require further longitudinal data. Maternal medication or substance use, such as certain chemotherapeutics or illicit drugs, can also transfer bioactive compounds, contraindicating breastfeeding in acute scenarios. In rare genetic disorders like classic galactosemia, breast milk's lactose content exacerbates metabolic crises, necessitating formula substitution from birth to prevent hepatic failure and sepsis. Delayed onset of lactation, observed in up to 25% of mothers with risk factors like obesity or cesarean delivery, heightens infant dehydration and hyperbilirubinemia risks if supplementation is not promptly provided. While overall benefits often predominate, these risks underscore the need for individualized assessment, especially in high-income contexts with viable alternatives.

Maternal Health Implications

Benefits to the Mother

Breastfeeding confers several health benefits to the mother, primarily through prolonged lactational amenorrhea and associated hormonal shifts that reduce cumulative exposure to endogenous estrogens and promote metabolic adaptations. A meta-analysis of epidemiological studies indicates that each additional 12 months of breastfeeding duration correlates with a 4.3% reduction in breast cancer risk, independent of parity effects. This protective association strengthens with longer cumulative lactation periods, potentially due to differentiated cell turnover in breast tissue during milk production, as evidenced by cohort data spanning decades. Similarly, breastfeeding lowers ovarian cancer risk, with systematic reviews reporting odds ratios as low as 0.72 for ever-breastfeeders compared to non-breastfeeders, attributed to suppressed ovulation cycles. Metabolic benefits include a diminished incidence of type 2 diabetes mellitus. Large prospective cohort studies, such as the Nurses' Health Study II, demonstrate that women breastfeeding for at least 6 months across parities experience up to a 47% lower risk of developing type 2 diabetes over 30 years, with dose-response patterns favoring extended durations. Meta-analyses confirm a relative risk reduction of approximately 40% for ever-breastfeeders, linked to improved insulin sensitivity and glucose homeostasis during lactation, independent of adiposity changes. Cardiovascular outcomes also improve, with observational data from population-based cohorts showing breastfeeding associated with 11% lower overall cardiovascular disease risk, 14% reduced coronary heart disease, and 12% decreased stroke incidence. These effects persist after adjusting for confounders like smoking and socioeconomic status, potentially mediated by favorable lipid profiles and reduced postpartum hypertension observed in lactating women. In the immediate postpartum period, breastfeeding promotes uterine involution via oxytocin release during suckling, reducing postpartum hemorrhage risk by up to 40% in meta-analyses of randomized trials comparing suckling to formula initiation. Extended lactation further aids maternal energy balance, facilitating gradual weight loss through increased caloric expenditure—approximately 500 kcal daily—without adverse effects on bone density recovery post-weaning. While psychological benefits such as enhanced maternal-infant bonding are reported in qualitative reviews, quantitative evidence for reduced postpartum depression risk remains inconsistent across studies, with some meta-analyses showing modest associations only for durations exceeding one month.

Contraindications and Health Burdens

Breastfeeding imposes significant physiological demands on the mother, including an estimated additional 300-500 kcal daily energy expenditure and heightened requirements for nutrients such as , , and , which can lead to maternal depletion if dietary intake is insufficient. Lactating women in undernourished populations face elevated risks of micronutrient deficiencies, with studies showing higher prevalence of and fatigue compared to non-lactating women of similar socioeconomic status. Inadequate caloric intake below 1,500 kcal per day may reduce milk volume while exacerbating maternal exhaustion. Physical burdens include nipple trauma, mastitis, and musculoskeletal strain from frequent feeding positions, affecting up to 10-20% of breastfeeding mothers in the early postpartum period and contributing to weaning decisions. Prolonged breastfeeding without adequate support can prolong postpartum recovery by delaying return to pre-pregnancy weight and increasing fatigue due to disrupted sleep patterns. Psychological burdens arise particularly from breastfeeding difficulties, such as latch issues or low supply perceptions, which correlate with increased maternal stress, anxiety, and symptoms of postpartum depression in observational studies. Traumatic experiences, including persistent pain or perceived failure, may undermine maternal self-efficacy and identity, with qualitative reports indicating emotional exhaustion akin to grief in severe cases. True contraindications to breastfeeding based solely on maternal health conditions are rare, as most infections or illnesses do not directly compromise the mother's well-being through lactation itself. However, active treatments such as , high-dose radiation, or certain antimetabolites necessitate temporary suspension to avoid exacerbating maternal toxicity or interfering with recovery. Untreated active requires isolation and pumping rather than direct feeding, primarily to protect the infant but also to prioritize maternal treatment adherence. In cases of severe maternal malnutrition or malabsorptive disorders, breastfeeding may perpetuate nutritional deficits, warranting supplementation or formula use to safeguard maternal health.

Practical Handling

Expression and Storage Methods

Breast milk expression involves removing milk from the breast when direct infant suckling is not feasible, such as during maternal separation or to build a supply. Methods include hand expression, which requires massaging the breast and compressing the areola to eject milk, and mechanical pumping using manual or electric devices. Hand expression demands practice but necessitates no equipment and can be performed anywhere. Manual pumps operate via hand-generated suction, while electric pumps, particularly double models, provide greater efficiency in milk volume extracted and reduced expression time compared to manual alternatives. Electric pumps mimic infant suckling patterns more effectively, yielding comparable volumes to direct feeding in skilled users. Typical single pumping sessions yield approximately 60–120 ml (2–4 oz) total for an average lactating woman, varying by factors such as pumping efficiency, session duration, and maternal supply. Prior to expression, hygiene protocols mandate hand washing and breast cleaning; pumps require inspection for cleanliness, with replacement of moldy parts to prevent contamination. Expression technique influences output: positioning fingers 1-2 inches behind the nipple optimizes milk flow from lactiferous sinuses. No significant differences in milk contamination rates occur between hand expression and various pump types when proper hygiene is maintained. Expressed milk storage guidelines emphasize temperature control to preserve nutritional integrity and inhibit bacterial growth. Freshly expressed milk remains safe at room temperature (up to 77°F or 25°C) for 4 hours. Refrigeration at 40°F (4°C) or below extends usability to 4 days. Freezing at 0°F (-18°C) in a standard freezer compartment preserves milk optimally for 6 months, acceptably up to 12 months, though deep freezers at the same temperature support 12 months or longer with minimal quality loss. In insulated coolers with frozen ice packs, milk sustains viability for 24 hours during transport. Storage best practices include using clean, BPA-free containers or bags, filling to 2-4 ounces to minimize waste upon thawing, and labeling with expression date and time. Thawing should occur gradually in the refrigerator over 24 hours, avoiding microwaves to prevent nutrient degradation and hot spots that risk scalding the infant. Once thawed, milk must be used within 24 hours and never refrozen. These durations derive from empirical studies on bacterial proliferation and nutrient retention, prioritizing safety over maximal extension.

Safety Protocols for Preserved Milk

Proper hygiene is essential before expressing and handling breast milk to minimize bacterial contamination. Caregivers should wash hands thoroughly with soap and water for at least 20 seconds prior to pumping or transferring milk. Pump parts in contact with milk must be cleaned after each use according to manufacturer instructions, typically involving washing with hot soapy water and air drying, or sterilizing daily. Expressed milk should be stored in clean, food-grade containers such as glass jars, hard plastic with tight-fitting lids, or specialized breast milk storage bags designed for freezing; avoid bottles with the #7 plastic recycling code due to potential BPA leaching. All containers must be labeled with the date and time of expression to ensure use of the oldest milk first. Storage durations for expressed breast milk vary by temperature to prevent microbial growth while preserving nutritional quality. Freshly expressed milk can remain safe at room temperature (up to 77°F or 25°C) for no more than 4 hours. In a refrigerator maintained at 40°F (4°C) or colder, it is safe for up to 4 days, ideally stored in the back where temperature is most stable. For longer preservation, freezing is recommended: in a standard freezer compartment (-4°F or -20°C or colder), up to 6 months is optimal, though safe up to 12 months; in a deep freezer, it remains safe for 12 months.
Storage ConditionDuration for Fresh MilkDuration for Thawed Milk
Room temperature (≤77°F/25°C)Up to 4 hoursUp to 1-2 hours
Refrigerator (≤40°F/4°C)Up to 4 daysUp to 1 day
Freezer compartment of fridge (-4°F/-20°C or colder)Up to 6 months (best); 12 months safeDo not refreeze
Deep freezer (0°F/-18°C or colder)Up to 12 monthsDo not refreeze
Thawing and warming protocols prioritize gradual temperature changes to avoid nutrient degradation and bacterial proliferation. Thaw frozen milk in the refrigerator overnight or under lukewarm running water, never using a microwave as it can create hot spots destructive to antibodies and unevenly heat the milk. Overheating, such as boiling or excessive warming beyond body temperature, destroys nutrients and immunological benefits like antibodies, creates hot spots or scorching, and standard guidelines advise against reusing overheated or rewarmed milk to prevent further degradation and bacterial risks. Once thawed, use within 24 hours if kept refrigerated and do not refreeze, as repeated freeze-thaw cycles increase contamination risk. Swirl gently to mix fat layers rather than shaking, which may damage components. For transport, use insulated coolers with frozen gel packs to maintain refrigeration for up to 24 hours. Spoilage indicators include a sour odor distinct from the usual sweet smell or soapy smell or taste resulting from elevated lipase enzyme activity, which breaks down fats during storage or freezing and is distinct from spoilage; this can be mitigated by scalding freshly expressed milk before storage if desired, though it preserves overall quality. Clumping upon thawing, or sliminess; such milk should be discarded regardless of storage time. While storage guidelines are evidence-based to limit pathogen growth like Staphylococcus aureus or E. coli, actual safety hinges on initial hygiene and equipment sterility, with studies showing low bacterial counts in properly handled milk even after extended freezing. Pooling milk expressed within 24 hours into one container is safe if cooled first, reducing waste while maintaining quality.

Alternatives and Comparisons

Infant Formula Equivalents

Infant formulas are manufactured products designed to approximate the macronutrient composition of human breast milk, typically providing around 65-70 kcal per 100 mL, with fats contributing approximately 50% of calories, carbohydrates 40%, and proteins the remainder. Modern formulas adjust protein ratios to more closely mimic breast milk's predominance of whey (about 60%) over casein (40%), reducing digestibility issues compared to earlier casein-heavy versions, though breast milk's proteins include unique bioactive elements like and absent in formulas. Carbohydrates in formulas primarily consist of lactose, similar to breast milk's 7% content, but lack the diverse oligosaccharide profile—over 200 human milk oligosaccharides (HMOs) in breast milk support selective gut microbiota growth, whereas formulas incorporate synthetic prebiotics like galacto-oligosaccharides (GOS) and fructo-oligosaccharides (FOS) in limited varieties and quantities. Fats in formulas derive from vegetable oils blended to emulate breast milk's fatty acid spectrum, including long-chain polyunsaturated fatty acids like DHA and ARA, which are now routinely fortified following evidence of their roles in neurodevelopment; however, breast milk's lipid globules feature a protective membrane with bioactive proteins and enzymes that enhance absorption and modulate inflammation, a structure not replicable in processed formula emulsions. Micronutrients such as vitamins and minerals are standardized in formulas to meet regulatory standards (e.g., Codex Alimentarius guidelines), often exceeding breast milk's variable levels to compensate for infants' needs, but this static fortification ignores breast milk's adaptive micronutrient adjustments based on maternal diet and infant signals. Despite these approximations, formulas cannot duplicate breast milk's bioactive components, including immunoglobulins (e.g., secretory IgA), live leukocytes, hormones, and growth factors that confer antimicrobial protection and influence long-term immune programming; attempts to add analogs like nucleotides or probiotics yield partial benefits but fall short of breast milk's dynamic synergy. Meta-analyses indicate that formula-fed infants consume higher volumes and exhibit faster weight gain, with altered body composition (higher fat-free mass but variable fat mass percentages) compared to breastfed peers, underscoring nutritional but not immunological equivalence. While formulas support adequate growth and prevent deficiencies when prepared correctly, epidemiological data link exclusive breastfeeding to reduced risks of infections, allergies, and obesity, benefits not fully matched by formula supplementation, even with human milk fortifiers. Regulatory bodies like the FDA classify formulas as safe alternatives but explicitly state they are not equivalent to breast milk, prioritizing maternal own milk where possible.

Animal-Derived Milks

Animal-derived milks, chiefly from cows and goats, have served as historical substitutes for human breast milk when maternal lactation was unavailable, but their unmodified use in infants under one year is discouraged due to nutritional imbalances and health risks. Cow's milk contains approximately 3.3 grams of protein per 100 milliliters, compared to 1 gram in human milk, imposing excessive renal solute load on immature kidneys and increasing dehydration risk. It also lacks sufficient iron, heightening anemia incidence, and its high casein content forms curds that hinder digestion in neonates. The American Academy of Pediatrics advises against introducing whole cow's milk before 12 months, as infants' immature digestive systems and kidneys are unprepared, increasing risks of intestinal bleeding and nutritional deficiencies such as iron deficiency anemia; exclusive breast milk or iron-fortified infant formula is recommended instead. Goat's milk shares compositional drawbacks with cow's milk, including inadequate folate levels leading to megaloblastic anemia and potential electrolyte disturbances like hypernatremia from high mineral content. Despite claims of easier digestibility owing to smaller fat globules and lower αs1-casein, which may reduce allergic responses in some cases, unmodified goat's milk remains unsuitable for exclusive infant feeding and has been linked to morbidity and mortality in historical and clinical reports. Human breast milk surpasses animal milks in bioavailability, featuring lipases for enhanced fat absorption absent in bovine sources and oligosaccharides promoting beneficial gut microbiota, which unmodified animal milks do not provide. For complementary feeding in infants aged 6-11 months, the World Health Organization conditionally endorses full-fat animal milks with rigorous hygiene protocols, but emphasizes or formula as primary nutrition. Historically, from antiquity through the 19th century, diluted cow's or goat's milk sustained orphans via wet nurses or vessels, yet pre-formula eras saw elevated infant mortality from such practices before processing mitigated risks. Modern infant formulas derive from animal milks but undergo modification—dilution, fat blending, and fortification—to emulate human milk's profile, underscoring the inadequacy of raw forms.

External Influences and Contaminants

Environmental Toxins and Pollutants

Human breast milk can contain environmental toxins and pollutants accumulated from maternal exposure through diet, air, water, and consumer products, including persistent organic pollutants (POPs) such as polychlorinated biphenyls (PCBs), dioxins, per- and polyfluoroalkyl substances (PFAS), and heavy metals like lead, mercury, arsenic, and cadmium. Recent systematic reviews from 2024-2025 confirm the presence of these heavy metals in breast milk, with levels influenced by maternal diet, environmental exposures such as mining, agriculture, and smoking, and geographic location; some studies report potential infant health risks like impaired growth or elevated exposure, while others find concentrations posing no significant hazard in many regions. These substances bioaccumulate in fatty tissues and transfer into milk via lipid-soluble pathways, with concentrations varying by geographic region, industrial activity, and maternal diet; for instance, higher levels of aluminum, zinc, arsenic, lead, mercury, and nickel have been detected in breast milk from women in industrial or mining areas compared to rural settings. PFAS, known as "forever chemicals," are particularly ubiquitous, appearing in breast milk globally at concentrations often 1% of maternal serum levels, though infants may face heightened vulnerability due to immature detoxification systems and potential endocrine disruptions. Despite this transfer, empirical evidence indicates that the nutritional and immunological benefits of breastfeeding—such as reduced risks of infections, allergies, asthma, obesity, diabetes, and cardiovascular disease—substantially outweigh potential harms from contaminant exposure in most cases, including those from heavy metals. Longitudinal studies show declining trends in certain POPs like dioxins in breast milk following regulatory bans, correlating with lower infant doses over time, while breastfeeding itself accelerates maternal elimination of lipophilic toxins, reducing her long-term burden. Comparisons with infant formula reveal that while breast milk may carry POPs and pesticides, formula often contains higher levels of heavy metals and mycotoxins, underscoring that no feeding method is contaminant-free but breastfeeding provides superior protective factors against broader health risks. Public health authorities, including the U.S. Agency for Toxic Substances and Disease Registry (ATSDR) and Environmental Protection Agency (EPA), recommend continuing breastfeeding even in areas with elevated PFAS, as no causal links have been established between milk-derived exposures and adverse infant outcomes that override breastfeeding's advantages. Mitigation strategies focus on minimizing maternal preconception and postpartum exposure, such as avoiding contaminated fish or PFAS-laden products, though formula supplementation may be considered in extreme high-exposure scenarios without proven efficacy in reducing net risks. Overall, the causal evidence prioritizes breastfeeding's empirical protective effects over speculative contaminant harms, with ongoing monitoring needed for emerging pollutants.

Pharmacological and Substance Impacts

Numerous pharmacological agents and other substances ingested by lactating mothers transfer into breast milk primarily via passive diffusion across mammary epithelial cells, with the extent determined by physicochemical properties such as lipid solubility, molecular weight (<500 Da favors transfer), protein binding (low binding increases free fraction available), and pKa (non-ionized form at milk pH 6.8-7.4 crosses more readily). Active efflux transporters like can limit transfer for some substrates, while uptake transporters may enhance it for others. Lipophilic substances concentrate in the fat phase of hindmilk, potentially leading to higher exposure during longer feeds. Infant exposure is quantified as the relative infant dose (RID), calculated as (milk concentration × daily milk intake / maternal dose) × 100%; an RID below 10% is generally deemed low risk, though neonates' immature hepatic metabolism and renal clearance can result in accumulation and amplified effects even at low levels. Prescription medications vary widely in transfer and safety; for instance, most beta-blockers like propranolol achieve milk-to-plasma ratios of 0.1-1, yielding RID <1%, with no adverse infant outcomes reported in monitored cases, though bradycardia risk warrants caution in preterm infants. Antidepressants such as sertraline exhibit low transfer (RID 0.5-2%), with meta-analyses showing no increase in infant sedation or developmental delays, supporting continuation during lactation for maternal mental health stability. Opioids like codeine metabolize to morphine via CYP2D6 polymorphism; poor metabolizers risk infant toxicity (e.g., apnea cases reported in 2006-2009), leading to recommendations against use, whereas short-term low-dose oxycodone (RID ~1%) is acceptable with monitoring for drowsiness. In substance use disorder treatment, methadone and buprenorphine transfer minimally (RID 0.1-2.6%), with cohort studies of over 1,000 exposed infants finding no excess adverse events versus formula-fed controls when mothers are stable, outweighing separation risks. Alcohol diffuses freely into milk, mirroring maternal blood levels with a peak 30-60 minutes post-ingestion and elimination half-life of 2-3 hours in adults but up to 13 hours in neonates due to low ADH activity. Doses exceeding 0.5 g/kg (roughly two standard drinks) yield detectable infant exposure, correlating with reduced sleep, altered motor development in observational studies (e.g., 2011 Finnish cohort), and acute sedation; chronic intake also suppresses oxytocin-mediated milk ejection and prolactin, decreasing supply by up to 20%. Guidelines advise abstinence or strict timing—wait 2-3 hours per drink to minimize peaks—over pumping and discarding, as levels decline naturally. Nicotine from tobacco smoking or vaping transfers as the parent compound and metabolite cotinine, with milk-to-plasma ratios of 2-3 and peak levels 30 minutes after exposure, resulting in infant doses equivalent to 1-2 cigarettes daily for heavy smokers. This exposure associates with reduced milk volume via prolactin inhibition (up to 15% drop in studies) and infant effects including colic, irritability, and shorter sleep duration, per randomized trials comparing smoked versus non-smoked groups. Quitting is optimal, but if continued, smoking post-feeding and avoiding secondhand smoke mitigates acute transfer. Caffeine crosses readily (milk-to-plasma ratio ~0.6-1), peaking in milk 1 hour after maternal intake, with an RID of ~1% for 300 mg daily; however, infants' 3-4 fold longer half-life (up to 80 hours) risks jitteriness, tachycardia, and insomnia at maternal doses >500 mg/day, as documented in case series of excessive consumers. Moderate intake (<3 cups ) poses negligible risk in term s. Illicit substances pose higher risks; achieves variable but high milk concentrations (up to 10-fold plasma), with case reports of infant seizures and respiratory depression prompting absolute . Amphetamines transfer substantially (RID 5-10%), linked to infant agitation and poor in exposed cohorts, though prescribed therapeutic doses show no consistent harm with monitoring. Cannabis THC persists in milk (detectable days after use, RID ~2-8% for chronic users), correlating with potential neurobehavioral alterations in animal models and limited data suggesting dose-dependent infant exposure; avoidance is recommended pending further longitudinal studies. Overall, for non-medical illicit use, cessation is advised due to unpredictable dosing and polydrug risks outweighing benefits.

Microbial and Viral Transmission Risks

Breast milk from infected mothers can transmit certain viruses to nursing infants, with transmission efficiency varying by pathogen, maternal viral load, and duration. Human immunodeficiency virus type 1 (HIV-1) is transmitted through , with studies estimating a 14-20% cumulative over 18-24 months in untreated mothers in resource-limited settings, though antiretroviral reduces this substantially. Human T-lymphotropic virus type 1 (HTLV-1) also transmits via breast milk, with rates up to 20-30% in endemic areas without intervention, linked to adult T-cell / development later in life. Human cytomegalovirus (CMV), prevalent in 50-90% of adults depending on region, frequently sheds into breast milk and transmits postnatally, causing symptomatic in 10-20% of preterm infants under 32 weeks , potentially leading to or neurodevelopmental issues. (HBV) DNA has been detected in milk, but transmission risk remains low with infant and prophylaxis, as does not significantly elevate rates beyond perinatal exposure. (HCV) RNA appears in milk intermittently, with rare documented transmission cases, though cracked nipples increase risk. virus has been identified in milk up to one month post-, but data during outbreaks is limited. Bacterial pathogens pose risks primarily through contaminated expressed milk rather than direct breastfeeding, as the latter benefits from skin-to-skin factors. Expressed milk in neonatal intensive care units has been linked to outbreaks of gram-negative infections, including and , with 175 reported cases from 2001-2023 resulting in 55 systemic infections and 13 deaths, often due to improper storage or handling. Other contaminants like species or can cause late-onset in vulnerable preterm infants if lapses occur during pumping or storage. While breast milk's native —dominated by beneficial genera like and —typically supports infant gut health, opportunistic pathogens from maternal infections (e.g., group B or mastitis-associated bacteria) may transmit during acute illness, necessitating temporary cessation until resolution. Mitigation strategies include maternal screening for high-risk pathogens like and HTLV-1, pasteurization for donor milk (which inactivates CMV and most but preserves some antibodies), and strict protocols for expressed milk handling to minimize . In low-risk scenarios, benefits often outweigh transmission risks for viruses like CMV, but empirical data underscore the need for individualized assessment based on prematurity and maternal status.

Non-Infant Applications

Therapeutic and Medical Uses

Donor milk, often pasteurized and provided through milk banks, serves as a therapeutic intervention for very preterm or very infants at high risk of (NEC), a severe intestinal condition. Randomized controlled trials and meta-analyses demonstrate that donor milk supplementation reduces NEC incidence by approximately 50% compared to preterm when maternal milk is insufficient, with relative risks ranging from 0.42 to 0.93 in aggregated data from multiple studies. This protective effect persists despite , which inactivates pathogens but may diminish some bioactive components, yet donor milk outperforms in preventing short gut syndrome and surgical interventions for NEC. Human breast milk exhibits antimicrobial properties attributable to components such as , cytokines, polyunsaturated fatty acids, and , which inhibit pathogens including agents and extended-spectrum beta-lactamase-producing . Clinical studies confirm these effects and , with breast milk demonstrating bactericidal activity against common infant pathogens and reducing acquisition of antibiotic-resistant strains in breastfed cohorts. In preterm infants, higher doses of expressed maternal milk act as a form of medical , correlating with decreased microbial and infection rates beyond nutritional provision. Topical application of breast milk has been investigated for and effects in conditions like wounds, dermatitis, sore nipples, and corneal abrasions. In vitro and small clinical trials indicate that mature breast milk promotes re-epithelialization, reduces netrin-1 expression, scavenges free radicals, and accelerates healing in models, with anecdotal and observational evidence supporting its use for mucosal infections and ulcers. For instance, topical breast milk combined with reduced dermatitis incidence in intervention groups, while its and growth factors aid dermal recovery without the risks of synthetic alternatives. Emerging research highlights the presence of multipotent stem cells in breast milk, capable of differentiating into neural, epithelial, and other lineages, with preclinical models showing integration into tissue and potential mitigation of injury or neurological damage. These cells may contribute to long-term developmental benefits, though human therapeutic applications remain investigational, limited by challenges in isolation, viability post-pasteurization, and ethical sourcing for non-neonatal uses. While promising for regenerative therapies, such as adjunct treatment for preterm injuries, clinical translation requires further randomized trials to substantiate efficacy beyond observational data.

Adult Consumption Practices

Adults consume human breast milk for purported nutritional, immunological, or therapeutic benefits, particularly among bodybuilders who use it as a dietary supplement, believing its natural growth factors such as IGF-1, along with nutrients, hormones, and calorie density, provide an edge for muscle growth, recovery, or bulking beyond standard protein sources; anecdotal reports claim better gains or energy levels. Individuals with chronic illnesses aim for immune enhancement, and in some intimate or fetishistic contexts. This practice has gained visibility through online marketplaces where donors sell excess milk, often without medical screening, leading to informal transactions; in these markets, niche sales to bodybuilders reach up to $5 per ounce as atypical examples. Proponents claim advantages such as superior digestibility compared to bovine milk, immune-boosting antibodies, and even potential anticancer effects, though these assertions stem largely from anecdotal reports rather than controlled trials. Scientific evidence supporting direct adult consumption remains absent, with reviews finding no studies demonstrating benefits beyond possible effects. Breast milk's protein content is low, approximately 1.0–1.2 g per 100 ml—far less than the 20–30 g per serving in whey supplements optimized for adult muscle hypertrophy—and its composition is tailored for infant growth rather than adult needs. Breast milk is optimized for infants' developing immune and digestive systems, where components like antibodies and human milk oligosaccharides promote immunity, gut health, and infection prevention; infants' higher gastric pH allows greater survival of these elements to the intestine, whereas adults' mature digestion, including lower stomach pH, degrades many protective components, reducing their efficacy. Its nutritional value is comparable to other dairy sources without unique superiority for adults, who can obtain similar benefits from a balanced diet while avoiding risks like microbial transmission. This undermines claims of efficacy for adult or performance enhancement. Components like human milk oligosaccharides (HMOs) show preclinical promise for modulating adult when isolated and supplemented, but ingesting whole milk does not equate to these targeted effects and lacks validation in human trials for non-infant use. Risks predominate in unscreened sources, including transmission of pathogens such as , , , and bacteria like or , due to absence of or donor testing. Milk from regulated banks, which undergoes screening and , mitigates some hazards but is intended for infants and not endorsed for adults, potentially diverting supply from vulnerable neonates. Contaminants like environmental toxins or medications in donors' systems further complicate safety. In relational dynamics, some lactating individuals feed partners for bonding or erotic purposes, termed adult breastfeeding or ; partners who have tasted it commonly describe a very sweet flavor, often compared to heavily sweetened almond milk, melted vanilla ice cream, sugary cereal milk, vanilla soy milk, or melon juice, with a milky texture and sometimes a grainy or slightly salty aftertaste, though reactions vary from surprisingly pleasant to off-putting due to the context of infant feeding, though this carries similar infectious risks without proven health gains for the recipient. Overall, experts from institutions like advise against adult consumption, citing unproven utility outweighed by documented perils.

Historical and Cultural Dimensions

Pre-Modern Practices and Wet Nursing

Wet nursing, the practice of employing a lactating to breastfeed an not her own, emerged as early as 2000 B.C. and persisted as a primary alternative to maternal across ancient civilizations, including , , , and , where no reliable substitutes like existed. In these societies, wet nurses were sought when mothers died in , suffered from insufficient production, or prioritized social duties over nursing, particularly among elites who viewed direct as beneath their status. Selection of wet nurses often emphasized physical and , rooted in ancient beliefs that breast milk transmitted not only nourishment but also the nurse's physical and psychological traits to the , influencing choices toward nurses perceived as robust and virtuous. In , wet nurses held esteemed roles within royal and noble households, selected for their affiliation with high-status families to ensure the child's vitality, with contracts governing terms like duration and compensation. Greek and Roman practices similarly institutionalized wet nursing, employing slaves, freedwomen, or lower-class freeborn women as nutrices in affluent homes; Roman parents frequently outsourced newborns to these caregivers, who resided with the family to provide continuous feeding. Contracts from Ptolemaic and formalized obligations, such as exclusive for fixed periods, though economic pressures on nurses—often compelled by —led to arrangements favoring hiring families. Despite these structures, wet nursing carried inherent risks, including the neglect or abandonment of the nurse's own infants, who faced elevated mortality rates due to inadequate alternative feeding, and potential disease transmission from the nurse to the foster child, such as or in later eras. Medieval European practices extended these traditions, with urban elites hiring rural wet nurses to sustain survival amid high maternal mortality; breastfeeding durations aligned with ancient guidelines, extending to 18-24 months in urban settings for optimal , though wet-nursed children sometimes weaned earlier if nurses returned home. Wet nursing provided a biologically superior option to pre-modern alternatives like animal milks or hand-fed paps, which lacked immunological protections and often caused digestive failures, but systemic exploitation persisted, as nurses' own bore the brunt of resource diversion, contributing to class-disparate infant outcomes. By the leading into the , the practice remained widespread among the wealthy, though emerging medical critiques highlighted lapses and ethical concerns over , presaging its decline with artificial feeding advancements.

Modern Policy Debates and Societal Pressures

International health organizations, including the (WHO), recommend exclusive for the first six months of life, followed by continued with complementary foods up to two years or beyond, citing reduced risks of , infections, and chronic diseases supported by meta-analyses of observational data. However, critics argue that this guideline overlooks maternal nutritional deficiencies in low-resource settings, where exclusive may exacerbate undernutrition without adequate caloric for the mother, as evidenced by studies showing potential growth faltering in such contexts. In the United States, the endorses similar durations but emphasizes individualized counseling, acknowledging that not all infants thrive exclusively on breast milk due to biological variations in supply or issues. Policy efforts to boost rates include workplace accommodations under the U.S. Fair Labor Standards Act, amended in 2010 to require reasonable break time and private spaces for pumping milk for up to one year post-birth, covering most employees regardless of employer size. As of 2025, a National Academies report advocates for a federally funded national strategy via the Department of Health and Human Services to enhance support services, alongside paid family leave, to address disparities where only 25% of U.S. infants meet the six-month exclusive goal, per CDC data. Debates persist over enforcement, with research linking supportive state laws—such as those in 23 states by 2009 expanding protections—to higher initiation rates, yet federal gaps in paid leave contribute to early cessation among working mothers facing return-to-work barriers. Societal pressures amplify these policies, with social norms and networks exerting influence that correlates with initiation but also negative outcomes; a 2024 study found perceived pressure to breastfeed associated with elevated , anxiety, and stress symptoms in over 1,000 mothers surveyed. Qualitative analyses reveal guilt and among those unable to meet expectations, often stemming from idealized portrayals in media and healthcare that frame as inferior, despite its nutritional adequacy when prepared correctly. Public breastfeeding laws, legal in all 50 U.S. states without restriction in locations where the mother is otherwise authorized, aim to normalize the practice, yet cultural stigma persists, prompting debates on whether promotion campaigns inadvertently heighten judgment rather than provide practical support like affordable pumps or peer counseling. Equity-focused policies target disparities, with programs like the CDC's Children Breastfeeding Friendly Communities Initiative implementing systems changes to reduce racial and socioeconomic gaps, where Black infants receive breast milk at half the rate of white infants per 2022 data. Critics of formula marketing, highlighted in a 2022 WHO report documenting violations in 15 countries via digital ads idealizing bottles over , advocate stricter regulations akin to the International Code of Marketing of Breast-milk Substitutes adopted in 1981. Nonetheless, overemphasis on without addressing root causes like inadequate maternity leave—averaging 12 weeks unpaid federally—fuels arguments for pragmatic policies prioritizing over ideological purity, as evidenced by correlations between extended paid leave in countries like and sustained breastfeeding rates exceeding 80% at six months.

Economic and Regulatory Framework

Donor Banking and Quality Controls

Donor human milk banks operate primarily as nonprofit entities that collect excess milk from screened lactating women, process it to ensure safety, and distribute it to vulnerable infants, particularly preterm neonates in neonatal intensive care units (NICUs). The Human Milk Banking Association of (HMBANA), founded in 1985, establishes voluntary standards adopted by accredited banks in the and , emphasizing preventive controls to mitigate biological, chemical, and physical hazards. These banks prioritize infants unable to receive their mother's own milk, with distribution often rationed based on medical need due to limited supply; for instance, HMBANA-accredited banks dispensed approximately 4 million ounces of milk in 2023 to over 6,000 infants annually. Donor screening begins with a detailed health questionnaire assessing , factors, and exclusion criteria such as active infections, recent tattoos or piercings, , or use of certain medications and illicit drugs. Prospective donors undergo serological testing for HIV-1/2, and C, human T-lymphotropic virus types I/II, and , with repeat testing required every six months or after high-risk exposures. Milk collection occurs at home under strict protocols, including use of sterilized equipment and immediate freezing at -20°C or lower, followed by transport to the bank in validated coolers. Unregulated informal milk , by contrast, lacks these controls and carries elevated risks of bacterial , with studies reporting higher prevalence in peer-to-peer transactions compared to banked milk. Processing involves pooling milk from multiple donors (typically 2-5 donors per batch to dilute potential contaminants), followed by Holder at 62.5°C for 30 minutes to eliminate viruses and while retaining partial nutritional and immunological properties. Post-pasteurization, batches undergo microbial culturing to verify sterility, with failures discarded; accredited banks maintain logs and conduct periodic audits under and critical control points (HACCP) frameworks. Storage occurs at -20°C for up to six months, with dispensing in sterile bottles traceable to donor and batch via barcoding. The FDA does not impose federal regulations on nonprofit milk banks but views milk as a requiring compliance with general standards, deferring to HMBANA guidelines for . Quality assurance extends to facility , requiring annual inspections, staff training in good manufacturing practices, and validation of equipment like pasteurizers via temperature probes and biological indicators. Peer-reviewed evidence confirms that these protocols render donor milk safe, with rates reduced by up to 75% in preterm infants receiving pasteurized donor milk versus , though bioactivity loss from limits equivalence to raw maternal milk. Some banks, like those affiliated with Prolacta Bioscience, employ additional filtration or sterilization for research-grade products, but standard HMBANA milk prioritizes accessibility over maximal preservation. State-level variations exist, such as Washington's WAC 246-720 mandating serological screening and for licensed banks. Despite robust controls, supply shortages persist, with demand exceeding capacity by factors of 10-20 in high-need regions, underscoring reliance on donor rather than commercial scaling.

Market Dynamics and Fraud Incidents

The market for human encompasses both regulated non-profit human milk banks and unregulated informal sales channels. Non-profit organizations like the Human Milk Banking Association of (HMBANA) distributed 9.2 million ounces of pasteurized donor milk in 2021, marking a 22% increase from 2020, primarily to neonatal intensive care units for preterm infants. This growth reflects rising demand driven by evidence of donor milk's benefits in reducing risk, though supply constraints persist due to donor recruitment challenges and processing costs, with prices ranging from $3 to $5 per ounce after . Emerging for-profit entities, such as those supplying fortified milk products to hospitals, have but raised ethical concerns over , including potential exploitation of donors and prioritization of profit over equitable distribution. Informal peer-to-peer sales dominate unregulated segments, facilitated by online platforms such as OnlyTheBreast.com and Facebook groups where milk trades for $0.50 to $1.50 per ounce in 2025-2026, with bulk sales often lower at 0.25−0.25-0.50 per ounce and many listings around $1 per ounce, varying by quantity, location, and specifics, often without screening for pathogens or proper storage verification. These transactions appeal to parents seeking alternatives to formula amid shortages or personal preferences, but they evade quality controls, leading to health risks from potential HIV, hepatitis, or bacterial contamination, as unscreened milk lacks the pasteurization standard of formal banks. The U.S. Food and Drug Administration advises against such purchases due to disease transmission risks, yet demand persists, with some sellers earning up to $1,000 monthly from high-volume pumping. Globally, informal markets surged in regions like China post-2013 formula scandals, where mothers sold milk amid distrust in commercial alternatives, though without regulatory oversight. Fraud incidents in breast milk markets typically involve or adulteration in informal . In 2024, a Georgia woman faced charges after scamming over 200 buyers across multiple states, including instances where purchasers shipped breast milk for purported custom services but received no product or deliverables, resulting in financial losses tied to irreplaceable biological materials. Such schemes exploit trust in online milk-sharing communities, amplifying emotional and economic harm beyond monetary value. Health authorities report sporadic cases of sellers diluting human milk with cow's milk or to increase volume, though verified prosecutions remain rare due to the decentralized nature of transactions. The absence of federal regulation on private —deemed legal but hazardous—perpetuates vulnerabilities, with experts advocating stricter oversight to curb while preserving access.

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