The Pharmaceutical Journal
Vol 277 No 7414 p227-230
19 August 2006

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Vitamin D — function and uses

Vitamin D has a number of essential functions in the body as well as several established clinical uses. In this article, Pamela Mason discusses the vitamin’s metabolism and interactions and looks at growing evidence of its involvement in other conditions

Continuing professional development articles

SUMMARY

Vitamin D was first identified in the early 1900s, when it was realised that cod liver oil contained a substance that could cure rickets. Strictly, it is incorrect to describe this substance as a vitamin because it can be synthesised in the skin; a dietary source only becomes essential when exposure to sunlight is inadequate. Moreover, vitamin D is converted to an active metabolite which acts like a steroid hormone, binding to receptors in a range of body tissues.

Its principle function is to maintain the plasma concentrations of calcium by actions in the intestine (to increase calcium absorption) the kidney (to reduce excretion of calcium) and the bone (to mobilise calcium, but later to replace bone loss).

Vitamin D has a number of other functions, including modulation of insulin secretion and the immune system. Vitamin D receptors have been found in more than 30 different tissues and the number of genes known to be regulated by calcitriol is growing, giving credence to the idea that vitamin D has functions beyond that of calcium regulation.

Vitamin D has several well-established clinical uses, including the treatment of deficiency states resulting from primary deficiency or deficiency secondary to malabsorption. In combination with calcium it has established benefits in the treatment of hypoparathyroidism. In combination with phosphorus, it results in improved calcium and phosphorus balance in patients with hypophosphataemia. Both liver disease and end-stage renal disease result in compromised hydroxylation of vitamin D to produce its active metabolite. Supplementation of vitamin D in renal disease, therefore, requires active forms or analogues of vitamin D.

Vitamin D is found naturally only in foods of animal origin, especially oily fish and fish liver oil, and in smaller amounts in egg yolk, dairy fat, liver and other offal. Some other foods are fortified with added vitamin D. In the UK, these include breakfast cereals, margarine, soya milk and other processed milks and infant foods.

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