Vitamin D and Calcium Dietary Supplements in the Elderly

Abstract

Calcium, in the form of calcium phosphate crystals, is the essential mineral component of the skeleton that confers both rigidity and strength to bone tissue. Deposition of calcium phosphate at the mineralization front, absorption of calcium from the diet, and regulation of calcium and phosphate homeostasis are dependent on the sufficiency of the vitamin D stores and their metabolism to biologically active forms of vitamin D. Skeletal calcium is derived solely from the diet (1). Because foods that are calcium rich are limited and because calcium absorption from the diet is normally only about 30 to 40% efficient, suboptimal calcium content of the skeleton may readily develop (2). This is not true for phosphate, except in neonates, and dietary deficiency only arises when dietary phosphate is bound within the gut by such medications as antacids containing aluminum hydroxide (3). Vitamin D stores are maintained by the production of vitamin D in the skin from the action of sunlight on 7-dehydrocholesterol. Only minor amounts are derived from dietary sources. Thus, vitamin D stores are readily depleted in populations with limited sunlight exposure (4). Calcium phosphate and vitamin D together are essential factors at all stages in the life of the skeleton from its development in the fetus, to its growth during childhood and adolescence, its consolidation in young adults to achieve peak bone mass and to its response to the aging processes.