Vitamin D: hope on the horizon for MS prevention?

The Lancet Neurology, Volume 9, Issue 6, Page 555, June 2010
doi:10.1016/S1474-4422(10)70121-6Cite or Link Using DOI

The Lancet Neurology

http://www.thelancet.com/journals/laneur/article/PIIS1474442210701216/

The worldwide prevalence and incidence of multiple sclerosis (MS) are on the increase. The need for strategies to prevent this devastating disease is therefore greater than ever. As highlighted in a Review in this issue of The Lancet Neurology, vitamin D deficiency might be an important modifiable risk factor for MS. This raises the question of whether population-wide supplementation programmes might be a reasonable prevention strategy.

Vitamin D deficiency is especially common in high latitude regions, such as northern USA, Canada, northern Europe, and New Zealand, where weaker ultraviolet B rays during winter months are insufficient for people to produce enough vitamin D. Vitamin D deficiency has traditionally been linked to bone diseases such as rickets; in addition to MS, links with other diseases such as type 1 diabetes, heart disease, infectious diseases, and some types of cancer are now emerging. Pregnant women, young children, and the elderly are at the greatest risk. Vitamin D deficiency might also adversely affect disease course in many disorders, including MS, although evidence for this is less robust.

The main sources of vitamin D are sunlight and diet, but many people do not get sufficient amounts, so dietary supplements are required. The current recommended daily intake of vitamin D is typically 200—400 IU/day in Europe, and in the USA and Canada, where some foods are fortified with vitamin D, the recommendation is for 200—600 IU/day. The US National Academy of Sciences' Institute of Medicine is currently reviewing the dietary reference intakes for vitamin D and calcium and is due to report its recommendations at the end of summer 2010. Expert recommendations for optimum serum vitamin D concentrations range from 50 nmol/L to 100 nmol/L; the total daily need for vitamin D, from sunshine, diet, and supplementation, to achieve this concentration is thought to be 1000—4000 IU/day, depending on factors such as age, geographical region, and health status. The risks of taking high doses of vitamin D are thought to be low, and the main concern of overdose is hypercalcaemia. However, given that an adult who spends 20 min in summer sunshine can produce an oral intake equivalent of about 10 000 IU/day, the suggested dose of 1000—4000 IU/day is unlikely to be toxic. Recent evidence suggests that prolonged intake of 10 000 IU/day (and even up to 40 000 IU/day) poses no risk for adults.

So far, the evidence for a protective effect of vitamin D on MS largely comes from ecological and observational studies, although evidence is accumulating on possible mechanisms linking vitamin D deficiency and autoimmunity. Large-scale, long-term randomised controlled trials on high-dose vitamin D supplementation would be needed to definitively establish a protective effect and to identify any unexpected long-term complications. But it could take decades before data on MS prevention become available.

In the meantime, because the risks seem to be low, is there already a case for widespread vitamin D supplementation? Scotland is one such region where the prevalence and incidence of MS, and other diseases related to vitamin D deficiency, are already so high that the benefits of supplementation are likely to outweigh any potential side-effects. During an upcoming summit in Scotland, hosted by MS Society Scotland and resulting from the Shine on Scotland campaign, researchers will present the case to Scottish government officials for vitamin D supplements to be made freely available for all young children and pregnant women. As vitamin D is an inexpensive supplement, the potential cost savings of such a programme are enormous, and in addition to MS, might have implications for numerous diseases linked to vitamin D deficiency. In Europe, if the predicted effects of raising serum vitamin D concentrations to 100 nmol/L are realised, the potential savings have been estimated to be €187 billion per year from the direct and indirect burden of disease, set against an expenditure of €10 billion on testing and public education. As well as the possible health benefits, such a supplementation programme might provide important research opportunities to understand the long-term effects of vitamin D.

Trials are needed to address the numerous questions that remain to be answered about dosing levels, potential long-term complications, and causal mechanisms, among others. In the meantime, given the low costs, low toxicity, and possible beneficial effects of supplementation programmes, steps to tackle vitamin D deficiency in high-risk populations seem warranted. Because any benefits for MS in particular will take decades to emerge, a long-term outlook is needed from policy makers, but future health and financial benefits have the potential to make this investment highly rewarding.

Many files and wiki pages on MS in the VitaminDWiki