By Mrinal Pandit, Chief Dietician, NephroPlus

Vitamin D deficiency is widely prevalent despite plentiful sunshine even in tropical countries like India. The prevalence of vitamin D deficiency is 70%- 80 % in the Indian sub-continent. Vitamin D is a fat-soluble vitamin available in a very few food groups. It is synthesized exogenously when sunlight strikes the skin.

Season, time of the day, length of the day, cloud cover, smog, skin melanin content and sunscreen are among the factors that affect UV radiation exposure and vitamin D synthesis. Complete cloud cover reduces UV energy by 50%; shade (including that produced by severe pollution) reduces it by 60%. UV radiation does not penetrate glass, so exposure to sunshine indoors through a window does not produce vitamin D.
Vitamin D obtained from sun exposure, food, and supplements is biologically inactive and must undergo two changes in the body for activation. The first occurs in the liver and converts vitamin D to D2, also known as calcidiol. The second occurs primarily in the kidney and forms the active product D3, also known as calcitriol.

Role of Vitamin D in the body:
• Maintaining Calcium and Phosphorus levels in the body.
• Maintaining healthy and strong bones.
• Prevents osteomalacia in adults and rickets in children.
• Inhibits parathyroid hormone secretion.

Vitamin D also appears to play a more extensive role as a cell differentiating and anti-proliferative factor with actions in a variety of tissues, including the renal, cardiovascular and immune systems.

Food sources of vitamin D

Recommended Dietary Allowance for Vitamin D

Patients with CKD have an exceptionally high rate of severe vitamin D deficiency that is further worsened by the reduced ability to convert inactive vitamin D into the active form. As kidneys’ ability to activate vitamin D is lost, patients with kidney disease have traditionally been given vitamin D replacement with active vitamin D or a related analog for better utilization.
Parathyroid glands secrete parathyroid hormone (PTH). PTH regulates serum calcium and phosphate, which in turn regulate PTH. The levels of calcium, phosphorus and parathyroid hormone should be tested regularly, as active vitamin D enhances the absorption of calcium and phosphorus and can lead to hypercalcemia and hyperphosphatemia. In such cases, discontinuing vitamin D therapy may be recommended.