Clinical Significance

Vitamin D is a lipid-soluble steroid hormone that is produced in the skin through the action of sunlight or is obtained from dietary sources.

The role of vitamin D in maintaining homeostasis of calcium and phosphorus is well established. Chronic severe vitamin D deficiency in infants and children causes bone deformation commonly known as rickets, while in adults, proximal muscles weakness, bone pain and osteomalacia may develop. Less severe vitamin D inadequacy may lead to secondary hyperparathyroidism, increased bone turnover, and progressive bone loss, increasing the risk of osteoporosis. The presence of the vitamin D receptor in other tissues and organs suggests that vitamin D may also be important in non-skeletal biological processes.

Vitamin D exists in two primary forms, vitamin D₃ (cholcalciferol) and vitamin D₂ (ergocalciferol). Vitamin D₃ is produced from the conversion of 7-dehydrocholesterol in the epidermis and dermis in humans upon exposure to sunlight, and can be found in oil-rich fish (e.g. salmon, mackerel, and herring), egg yolks, and from foods supplemented with vitamin D. Vitamin D₂ is found in certain plants and mushrooms.

_{Source: Beckman Coulter, Inc. Access 25(OH) Vitamin D Total product insert, Brea, CA 92821, P/N B29609A}