The great positive impact of public health programs is widely acknowledged. Due in part to the policies and actions developed through public health, the 20th century registered a decrease in the mortality rates for infants and children and a continual increase in life expectancy in most parts of the world. For example, it is estimated that life expectancy has increased for Americans by thirty years since 1900, and worldwide by six years since 1990.
Genetics, or inherited traits from parents, also play a role in determining the health status of individuals and populations. This can encompass both the predisposition to certain diseases and health conditions, as well as the habits and behaviors individuals develop through the lifestyle of their families. For example, genetics may play a role in the manner in which people cope with stress, either mental, emotional or physical. For example, obesity is a significant problem in the United States that contributes to bad mental health and causes stress in the lives of great numbers of people. (One difficulty is the issue raised by the debate over the relative strengths of genetics and other factors; interactions between genetics and environment may be of particular importance.)
Autoimmune diseases are a group of disorders in which the immune system attacks the body and destroys or alters tissues. There are more than 80 serious chronic illnesses in this category, including lupus, multiple sclerosis, and type 1 diabetes. According to the American Autoimmune Related Diseases Association (AARDA), about 75% of autoimmune diseases occur in women. By themselves, each disease appears to be uncommon except for diabetes, thyroid disease, and lupus but as a group, the disorders make up the fourth-largest cause of disability among American women.