Vitamin D3

Vitamin D has been known since 1920 as a chemical and nutritional entity. Not until after the late 1960s, however, has the biochemical basis of its physiological role been at least partially defined. Since then, research in vitamin D metabolism has resulted in new and important information regarding its role in calcium and phosphorus metabolism. Research has also given insights into the value of vitamin D in clinical medicine related to abnormal mineral metabolism, endocrinology, and nutrition.
Vitamin D can be considered a vitamin only in the sense that, under modern farming conditions, many animals are raised in total confinement with little or no exposure to natural sunlight. Adequate sunlight results in the production of sufficient vitamin D3 from 7-dehydrocholesterol in the skin. Lack of adequate photoproduction of vitamin D3 or inadequate dietary supplementation of vitamin D leads to the failure of bones to calcify normally. This metabolic disease is known as rickets in the young and osteomalacia in adults.