Vitamin D supplementation-clarity required regarding treatment regimens and target plasma levels

The discovery of vitamin D at the beginning of the twentieth century was the result of pioneering work by numerous researchers investigating the role of vitamins and other factors in disease prevention. This culminated in Adolf Windaus being awarded the Nobel Prize for Chemistry in 1928 for his work on steroid chemistry and vitamins.1 Vitamin D deficiency is prevalent in healthy adults and is particularly high among black and Asian subjects living at higher altitudes. The National Health and Nutritional Examination Survey 2006 reports an overall prevalence rate of vitamin D deficiency of 41% in US adults.2 Older people and those who are institutionalized are more likely to have vitamin D deficiency and a UK survey found that only 16.2% of men and 13.2% of women aged ≥65 years had serum 25(OH)D levels ≥75 nmol/l.3 It is apparent but poorly understood that a strong association exists between socio-economic disadvantage and poor health in northern Europe and North America. Grimes4 suggests that poorer health and shorter life expectancy of the socio-economically disadvantaged in the UK may be partially explained by an association with the relative deficiency of vitamin D. Very few foods contain vitamin D2 or vitamin D3 and therefore, unlike other vitamins, humans rely primarily on sun exposure to obtain vitamin D. Vitamin D exerts its action through vitamin D receptors which are found in most cellular tissues. These receptors have a wide range of important biological actions including inhibition of cellular proliferation and induction of terminal differentiation, inhibition of angiogenesis, stimulation of insulin production, inhibition of renin production and stimulation of macrophage cathelicidin production.4 Vitamin D is therefore essential for normal calcium homeostasis but also has many other roles in cellular metabolism including modulation of cell growth, neuromuscular and immune function and reduction of …