Abstract

Over the last decade there has been considerable evolution of our understanding of vitamin D metabolism and its biological activity. The discovery that most tissues and cells in the body have vitamin D receptors and that several possess the enzymatic machinery to convert the primary circulating form of vitamin D to its active form, 1,25-dihydroxyvitamin D, has provided new insights into the function of this vitamin.  Aside from calcium homeostasis vitamin D has been demonstrated to exert a wider range of biological activities including regulation of cellular differentiation and proliferation, immune functions, reproduction, and of special significance is to note its role in reducing the risk of many chronic illnesses, including common cancers, autoimmune diseases, infectious diseases, and cardiovascular disease. Although it is fascinating that its in vitrobiological activities were previously known in the past 2 decades, the physiological context of these is showing proof in many human studies now. Undiagnosed vitamin D deficiency is very common and 25-hydroxyvitamin D is the barometer for vitamin D status. Magnitude of this vitamin deficiency is so massive that unless some substantial measures are taken for its correction with supplementation, appropriate sun exposure and public education we may go back to where we were in 19th century, in terms of skeletal health and other newly discovered problems with vitamin D deficiency, when seeing patients with advanced rickets and osteomalacia was not an uncommon sight at all.

Key words: 25(OH) D, 25-hydroxy vitamin D; 1,25(OH)₂D, 1,25-dihydroxy vitamin D.