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Publisher Summary This chapter provides an overview of vitamin D. In contrast to vitamin A, vitamin D is stored in relatively small amounts in the animal body, and, therefore, is more readily depleted. It functions mainly as a regulator of the calcium–phosphorus balance of the body. This is achieved by increasing the intestinal absorption of calcium and phosphorus, by the mobilization of phosphate from the tissues, and by the control of the transfer of calcium and phosphorus between blood and bone. Vitamin D in adequate amount raises the calcium and phosphate to such a level in the tissue fluid that calcium salts become precipitated in the bone matrix when there is need for growth or remodeling of bone. In early postnatal life, the pituitary growth hormone is concerned, and at all stages, the parathyroid hormone in close association with vitamin D exercises a regulatory influence on the turnover of bony metabolites. The most important function of vitamin D is the hormonally assisted transfer of calcium, magnesium, and zinc from the intestinal canal to the plasma. The chapter also discusses vitamin D deficiency and vitamin D excess. Vitamin D deficiency alone apparently has no direct effect on thyroid function. Adrenalectomy of itself does not interfere with the known activities of vitamin D. |
