The 19th Century was the real heyday of discovery when it came to the enigmatic role that vital amines (or vitamins as they came to be known) play in human physiology. That our bodies could be so dependent on minute quantities of these mysterious substances was demonstrated profoundly in the cure of the dreaded disease of scurvy, by the simple provision of limes to sailors. The prevention of beriberi, rickets and other diseases of deficiency soon followed, and in the early 20th century all the scientists had left to do was to identify and purify the dietary compounds responsible.
We are never likely to cure a vitamin-related disease in one fell swoop in quite the same way again, but there is still much to be learnt about the role they play, and the possibility that a relative deficiency in a single vitamin might influence our risk of developing a particular disease. High on that list is multiple sclerosis (MS), a debilitating disease of the nervous system, and its relationship with Vitamin D. Although we do not know the cause of MS, we can be sure that it is not simply a matter of deficiency – many people have low Vitamin D levels and do not develop MS, while many of those who do develop it will have normal levels of the vitamin. Genetic factors and other environmental triggers will certainly play their part. The question is – does a low level of Vitamin D make you more susceptible?
Well, there is some compelling circumstantial evidence. One of the most striking reasons to think about Vitamin D in particular is the unusual geographical incidence of the disease. This is beautifully demonstrated on this map, based on WHO data. Whatever explanation we come up with for MS, it has to account for the remarkable predilection that the condition has for increasing latitude away from the equator – something that also makes it a pressing issue in the northern climes of the United Kingdom. That sunshine is our most potent source of Vitamin D is something I have already commented on in this blog, and this is clearly a commodity the equator has in abundance compared with the poles. There is also evidence of an association between low blood levels of Vitamin D and the development of MS, and only last week, new research was published from Oxford which suggested that at least some of the genetic link could be related to problems with Vitamin D.
The Oxford study was clever in its approach. They took about 1500 children with MS and looked at the genetics of their parents, to see if they were carriers for a genetic defect known to be linked to Vitamin D deficiency. If a child inherits two copies of the gene (one from each parent) then they develop a congenital form of rickets due to severe Vitamin D deficiency, but being a carrier for the genetic defect is not thought to be a problem. They discovered that of the 3000 parents, 35 of them were carriers for the gene. In itself that is not too remarkable. That means 2965 parents did not have the gene and yet had a child who developed MS – hardly evidence of a strong genetic cause. What was interesting, though, is that in all 35 cases the affected child inherited the genetic defect. Left to chance you would expect only 50% of the children to have inherited the gene – as the researchers say, it is like tossing a coin 35 times and getting heads every single time. Interesting indeed!
The problem is that all this evidence, good as it is, is circumstantial – there is no proof of cause and effect. It is rather like finding the candlestick that killed Colonel Mustard in the library with Miss Scarlett’s fingerprints on it – good, but not quite good enough to make a conviction – maybe she just liked polishing candlesticks? What we want to know is this: Would taking Vitamin D supplements help to prevent MS, or help avoid relapses in people who already have MS? To answer those questions we need a large, randomised study where thousands of people are given either the vitamin or placebo, and a second, similar study in people who already have MS.
The problems are these: The first study has to be large, and large means expensive. Vitamin D is cheap and generically available which means drug companies will not be interested in making an investment, leaving the cost to fall on research charities and governments in these austere times. The second study can be smaller, since episodes of relapse in people who have MS will be much more frequent than new episodes of MS in the general population, but how do you stop people with MS from taking Vitamin D on their own initiative? The placebo arm of the study will not be much of a placebo if everyone is also obtaining the vitamin from their local pharmacist. If I had MS would I take it? Well, yes. On the grounds that Vitamin D supplements (at normal levels) are safe and probably a good thing anyway, I think I could be convinced on even circumstantial evidence.