Exogenous factors influencing calcium and bone metabolism

Intestine and kidney play a central role in the regulation of calcium and b one metabolism. Total daily calcium loss must not exceed the amount of abso rbed calcium to avoid a loss of bone mass. Mechanical forces and several nu trients are among the exogenous factors influencing calcium and bone metabo lism. Gymnastics leading to enhanced mechanical forces on specific skeletal sites result in a renal calcium conservation and may prevent bone loss in postmenopausal women. Microgravity and strict bed rest, on the other hand, promote bone atrophy. In these cases, renal calcium excretion is increased and the intestinal calcium absorption rate decreased. Oral calcium intake m ay reduce bone resorption processes within few hours. Vitamin D promotes in testinal calcium absorption and to some extent compensates for a low dietar y calcium supply In the case of adequate calcium intake, however, the surpl us of calcium absorbed is excreted by the kidney. Vitamin Ii deficiency res ults in calcium utilization disorders of the bone and is associated with en hanced renal calcium loss. In malnourished patients with anorexia nervosa, disorders of the bone metabolism and renal calcium loss are especially pron ounced.