Clinical Significance

Vitamin D is a steroid hormone involved in the intestinal absorption of calcium and the regulation of calcium homeostasis. Vitamin D is essential for the formation and maintenance of strong, healthy bones. Vitamin D deficiency can result from inadequate exposure to the sun, inadequate alimentary intake, decreased absorption, abnormal metabolism, or vitamin D resistance Recently, many chronic diseases such as cancer, high blood pressure, osteoporosis, and several autoimmune diseases have been linked to vitamin D deficiency. Whether consumed or produced, both forms of vitamin D (D2 and D3) are metabolized by the liver to 25(OH) vitamin D, and then converted in the liver or kidney into 1,25‑dihydroxyvitamin D. Vitamin D metabolites are bound to a carrier protein in the plasma and distributed throughout the body. The most reliable clinical indicator of vitamin D status is 25(OH) vitamin D because serum and plasma 25(OH) vitamin D levels reflect the body’s storage levels of vitamin D, and 25(OH)vitamin D correlates with the clinical symptoms of vitamin D deficiency.