A hormone produced by the ovaries and testes. It stimulates the development of secondary sexual characteristics and induces menstruation in women. Estrogen is important for the maintenance of normal brain function and development of nerve cells. Estrogen is used therapeutically to treat breast and prostate cancer, osteoporosis and to relieve the discomforts of menopause. Some research suggests that estrogen may be beneficial in preventing Alzheimer’s disease. More studies are needed to confirm this.