Vitamin D Deficiency And Its Related Health Effects: An Indian Perspective

Vitamin D is a fat soluble vitamin that has mainly two types D2 (ergocalciferol) and D3 (cholecalcifererol). While vitamin D can be obtained from dietary sources (D2 isoform) the biggest contribution to an individual’s circulating levels of vitamin D, in most countries, is through endogenous production in the skin following exposure to ultraviolet(UV)-B radiation from the sun. Exposure to UV-B (wavelength ~290–315 nm) converts 7-dehyrdrocholestrol in the skin into pre-vitamin D (D3 isoform) which spontaneously isomerizes into vitamin D. This vitamin D, along with any vitamin D obtained through the diet, is converted into 25(OH)D in the liver. 25-Hydroxyvitamin D is the most abundant circulating metabolite of vitamin D. Almost all vitamin D produced in the skin or obtained from food or supplements is converted in the liver to 25 OHD1. Moreover, the serum half-life of 25-OHD is almost 2–3 weeks. Thus, serum 25-OHD level is a sensitive index of vitamin D status. The development of radio assays for 25-OHD 40 years ago has made it possible to measure serum 25-OHD concentration and to define an individual’s vitamin D status. Early studies indicated that serum 25-OHD under 5–8 ng/ml is invariably associated with rickets in children and with osteomalacia in adults, and levels under 12–15 ng/ ml are usually associated with secondary hyperparathyroidism or subtle osteomalacia. WHO has defined vitamin D insufficiency as level of serum 25-OHD less than 20 ng/ml. However, many studies have defined vitamin D deficiency as serum 25OHD level below 20 ng/ml and vitamin D insufficiency as levels 20-30 ng/ml.