Lifestyle diseases can be defined as the diseases linked to the manner in which a person lives their life. These diseases are non-communicable, and can be caused by lack of physical activity, unhealthy eating, alcohol, substance use disorders and smoking tobacco, which can lead to heart disease, stroke, obesity, type II diabetes and lung cancer. The diseases that appear to increase in frequency as countries become more industrialized and people live longer include Alzheimer's disease, arthritis, atherosclerosis, asthma, cancer, chronic liver disease or cirrhosis, chronic obstructive pulmonary disease, colitis, irritable bowel syndrome, type 2 diabetes, heart disease, hypertension, metabolic syndrome, chronic kidney failure, osteoporosis, PCOD, stroke, depression, obesity and vascular dementia.

Concerns were raised in 2011 that lifestyle diseases could soon have an impact on the workforce and the cost of health care. Treating these non-communicable diseases can be expensive. It can be critical for the patient's health to receive primary prevention and identify early symptoms of these non-communicable diseases. These lifestyle diseases are expected to increase throughout the years if people do not improve their lifestyle choices.

Some commenters maintain a distinction between diseases of longevity and diseases of civilization or diseases of affluence. Certain diseases, such as diabetes, dental caries and asthma, appear at greater rates in young populations living in the "western" way; their increased incidence is not related to age, so the terms cannot accurately be used interchangeably for all diseases.

Diet and lifestyle are major factors thought to influence susceptibility to many diseases. Substance use disorders, such as tobacco smoking, excessive consumption of alcohol, and a lack of or too much exercise may also increase the risk of developing certain diseases, especially later in life.

In many Western countries, people began to consume more meat, dairy products, vegetable oils, tobacco, sugary foods, sugary beverages, and alcoholic beverages during the latter half of the 20th century. People also developed sedentary lifestyles and greater rates of obesity. Rates of colorectal, breast, prostate, endometrial and lung cancer started increasing after this dietary change. People in developing countries, whose diets still depend largely on low-sugar starchy foods with little meat or fat have lower rates of these cancers. Causes are not just from smoking tobacco and alcohol use; adults can develop lifestyle diseases through behavioral factors that impact them. Behavioral factors including unemployment, unsafe life, poor social environment, working conditions, stress and home life can increase their risk of developing one of these non-communicable diseases.

Between 1995 and 2005, 813,000 Australians were hospitalized due to alcohol. In 2014, 11.2 million Australians were overweight or obese.

In 2013, there were 147,678 deaths within Australia mostly from lifestyle diseases. Smoking tobacco, alcohol use and other substances, violence, and unhealthy weight have impacted the Australians' death rate. The leading cause of death of Australian males was heart disease with 11,016 deaths, followed by lung cancer with 4,995 deaths, and chronic pulmonary disease killing 3,572. All these conditions were mainly attributed to smoking, excessive alcohol use or an unhealthy lifestyle. In 2013, coronary heart disease was the leading cause of death in 8,750 women, mainly as a result of their lifestyle. Dementia and Alzheimer's disease came second, affecting 7,277 females and thirdly, cerebrovascular disease, killing 6,368. These top three causes of deaths could be minimized through lifestyle changes within the Australian population.

The table shows the ages of people dying and the top five diseases for which they are dying.