Dehydroepiandrosterone (DHEA) is a steroid hormone secreted primarily by the adrenal glands and to a lesser extent by the brain, skin, testes, and ovaries. It is the most abundant circulating steroid in humans and can be converted into other hormones, including estrogen and testosterone. It has been characterized as a pleiotropic "buffer hormone," with receptor sites in the liver, kidney, and testes, and has a key role in a wide range of physiological responses. Circulating levels of DHEA decline with age and a relationship has been suggested between lower DHEA levels and heart disease, cancer, diabetes, obesity, chronic fatigue syndrome, AIDS, and Alzheimer's disease. Other research suggests that autoimmune diseases such as systemic lupus erythematosus (SLE), rheumatoid arthritis, and multiple sclerosis might be associated with declining DHEA levels.