Osteoporosis: gender differences and similarities.

Although osteoporosis has traditionally been considered a disease of women, men also incur substantial bone loss with aging, and elderly men have age-specific hip fracture incidence rates and vertebral fracture prevalence rates that are at least half those in women. Early postmenopausal bone loss (which results in the syndrome of type I osteoporosis) is due to the direct skeletal consequences of estrogen deficiency, manifested by an increase in bone resorption without an adequate increase in bone formation. Recent evidence indicates that even late postmenopausal bone loss (type II or 'smile' osteoporosis) in women may be due to estrogen deficiency. In particular, the late consequences of estrogen deficiency in elderly women result in abnormalities in calcium homeostasis and increases in parathyroid hormone secretion, leading to increased bone resorption and bone loss. The etiology of bone loss in aging men has remained relatively unclear. Recent evidence from a male deficient in estrogen receptor-alpha and in two males with aromatase deficiency indicate that estrogen may play a significant role in bone metabolism in men. Moreover, several large epidemiologic studies have found that bone mineral density correlates better with serum estrogen than testosterone in aging men. Thus estrogen deficiency may lead to bone loss in men.