Peterson M.E.

J Am Vet Med Assoc, 1982. 181(11): p.1434-1436.

Vitamin D and Parathyroid hormone play important roles in maintaining normal circulating concen- trations of calcium and phosphorus. Vitamin D is obtained from dietary sources and produced endoge- nously from precursors in the skin. Ultraviolet irra- diation ofergosterol, a sterol found in certain plants, produces vitamin D, (ergocalciferol). In the skin, ultraviolet light converts 7-dehydrocholesterol, a by- product in the synthesis of cholesterol, to vitamin D, (cholecalciferol)