Vitamin D: too much of a good thing?

Abstract

Vitamin D is increasingly recognised as an important sterol hormone, with some suggesting that it should be renamed ‘hormone D’.1 Vitamin D receptors are widely expressed throughout the body accounting for its regulatory role beyond the confines of the skeleton, including the immune system, pancreas, brain, and cardiovascular system.2 Consequently, vitamin D deficiency is implicated in diseases such as diabetes, multiple sclerosis, cardiovascular disease, and increased mortality.2 Research interest in vitamin D has grown by more than 250% in a decade and publications in 2012 almost equalled the research output for vitamins A, B, C, and E combined. Vitamin D deficiency is highly prevalent among the UK population; 35% of otherwise healthy Scottish adults are severely deficient and a further 29% are at high risk of deficiency,3 with northerly latitude, poor summers, reduced sun exposure, increasing use of sun protection, and an ageing population being contributory. The benefits of treating deficiency are revealed in meta-analyses showing reduced risk of fractures and falls in older people,4 as well as reduced cardiovascular and overall mortality.5 The joint letter from the Chief Medical Officers (CMOs) to UK health professionals6 supports the importance of vitamin D sufficiency as a public health priority by advocating treatment for young, pregnant, and older adults. As a consequence there has been an unprecedented increase in vitamin D prescribing. Since 2008, vitamin D monotherapy in primary care in England has increased exponentially in terms of both quantity …