There is a sound rationale for supplying supplements of vitamin D to the Scottish population. The case that deficiency contributes to their relative health deficit has recently been outlined in The Times and deserves timely consideration. I wish to add some additional perspective.

Human beings have spent most of their evolutionary history in tropical and sub-tropical regions where dark skin provides useful protection against intense sun. As man migrated north into Europe thousands of years ago, white skin became a necessary adaptation because it allows for more vitamin D production, and vitamin D is essential for good health.

The sun is too weak in Northern Europe to enable vitamin D to be made for several months of the year, but white skin enables people to make use of the thin spring or autumn sunlight of the kind we may get at these times of year and so extend the season when vitamin D can be made. There is increasing circumstantial evidence for an important role of vitamin D deficiency in “juvenile onset” diabetes, multiple sclerosis and in the onset of some cancers.

Scientists yearn for proof that these diseases are influenced by insufficient vitamin D. But such proof will be hard to come by. We know from laboratory evidence that many genes are regulated by vitamin D. A thousand genes (one in 30) have vitamin D response elements, stretches of DNA to which vitamin D complexes bind to exert this effect. This makes D-related genes one of the largest gene families in the genome. Most of these genes are unrelated to bone and calcium, the familiar context for this vitamin-hormone. The way most of these genes work and relate to vitamin D is not yet understood in detail, but there will be many more functions yet to be identified.

Vitamin D is important for foetal and child development and the evidence is increasing that deficiency early on will have later consequences. We know that the majority of Scots have sub-optimal levels in their blood and most, at winter's end, are deficient in it. The epidemiology of multiple sclerosis (MS) has been studied extensively and the best correlates of prevalence are with latitude and sunshine. Those with the same origins differ markedly for MS risk by geographical location.

Tasmanians have five to six times as much MS as do Queenslanders, but half as much as Scots, who have the highest rate in the world. Sunlight via an effect on vitamin D production remains the best candidate for this effect. The responsible factor appears to operate early in life.

We all would like definitive proof to support supplementation on a population level, meaning a trial to see what happens when some people are given the vitamin and others are not. It has been possible to carry out cancer prevention trials, but a trial to see if vitamin D will prevent MS and other later onset diseases might take some 25 years or more to complete.

It is plausible that some 200 cases a year of MS might be prevented in Scotland alone by giving vitamin D to mothers and children. Over a trial duration of 25 years, 5,000 cases of this disease might be otherwise prevented. The economic impact of each person with MS is at least an extra million pounds during a lifetime. Over 25 years, £5billion is at issue in this disease without factoring in the human cost, the increasing rate of MS or inflation. A large-scale programme providing vitamin D could provide scientific evidence.

Vitamin D is cheap and the organisation needed to provide it to mothers and babies already exists. There remains room for debate, but if D deficiency accounts for even some of Scotland's health deficit, timely action is needed.

Experts familiar with the vitamin D story are taking the vitamin and exposing themselves more to the sun as well. There is a large safety margin for vitamin D intake and concerns about amounts under consideration here have proven unfounded. It would make as much or more sense to ban holidays in Portugal as to fear increasing the low amounts of vitamin D that are recommended at present in the UK. Increased intake is now recommended by the Canadian Cancer Society, the National Academy of Sciences (USA), and the dietary committee of the European Union.

In another era it was said in jest that the reason fundamentalists in the southern US banned sex before marriage was because they were afraid it might lead to dancing. Are we worried about the sex or the dancing here?

The author is the Action Research Professor of Clinical Neurology at the University of Oxford

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