Osteoporosis affects at least 10 million Americans—most of whom are women.  Each year, more than 1.5 million fractures related to osteoporosis occur in the United States. One in two women older than 50 years will have a fracture related to osteoporosis in their lifetime. Fractures can be  crippling and painful and cause lifelong disability. Osteoporosis can pose a special threat to women. Estrogen—a female hormone—protects against bone loss. As a woman nears menopause, her body produces less estrogen. Hormone therapy slows bone loss after menopause. Estrogen has been shown to decrease the risk of hip fractures and spinal deformities. In women who have a uterus, estrogen is given along with another hormone—progestin.  This decreases the risk of endometrial cancer, which occurs when estrogen is given alone.