Saturday, 16 July 2011

You are my sunshine: vitamin D and autism

Historically, England and Scotland have perhaps not enjoyed the best of relationships. Anyone who has watched the blood and guts of the film Braveheart, very, very, very loosely based on the life and times of Sir William Wallace, will get an idea of what the main problems were in terms of conquest, lands, identity and freedom. Down the years some degree of one-upmanship still survives as evidenced by little things like the 'anyone but England' slogan during the recent World Cup. Those who watched the 2010 World Cup will know that the English football (soccer) team did pretty well on their own in early-exiting the tournament without the help of the ABE campaign.

As an Englishman living fairly close to the Borders, I don't want to get too involved in the politics. My geographical proximity to Scotland does however give me a little bit of a flavour of the climate in Scotland and its relevance to this post on vitamin D.

I was intrigued by a comment made to me quite recently when discussing measuring levels of vitamin D. The comment included the term 'normal for Scotland' when interpreting some biochemical results on vitamin D levels in various patient groups. I found out that day that 'normal for Scotland' is usually taken to mean vitamin D results are not abnormal when compared to the Scottish population but neither do they show a particularly healthy level of vitamin D to be present assuming accuracy of the testing procedure. One of the possible reasons: well whilst the sun does shine in Scotland (sometimes), there is quite a bit of evidence to suggest that it doesn't necessarily translate into an all-year round adequate vitamin D level for many, many people living at certain geographical coordinates all of which cover Scotland; indeed also where I live.

I should perhaps back-up a little and provide a little more description of vitamin D first. Vitamin D is a fat-soluble vitamin. Although having multiple uses throughout the body, vitamin D is perhaps most famous for its role in aiding in the absorption of calcium; see my recent post on this subject. There are a few ways of getting vitamin D; through our modern fortified diet (assuming you eat breakfast cereals for example) and also by contact with sunshine, or more specifically via exposure to ultraviolet B light. I suppose a third way is via supplementation.

Vitamin D is a vitamin in the spotlight at the moment. There is quite a lot of research coming out telling us how much we need vitamin D for lots of different health reasons, ranging from cancer prevention to maintaining good cognitive health to potentially helping to tackle growing health problems like diabetes. Looking at childhood health in particular, there is some pretty good evidence that conditions classically associated with vitamin D like rickets might be making an unwelcome return here in the UK and beyond. Although not altogether clear as to what is driving our vitamin D deficiency, it seems as though lifestyle is a possible factor; so sitting reading blogs from a home PC indoors rather than reading them on an iPad outdoors, our use of barrier creams to prevent excessive sun exposure and its onward effects, but also physiological factors such as skin colour (although research in this area is not cut and dried).

There is also some suggestion that vitamin D might show some connection to various childhood developmental conditions including autism. Vitamin D and psychiatry have, what might be called, a blossoming relationship. PubMed lists over 100 entries based on the keywords vitamin D and schizophrenia, covering various angles of a possible connection from genes to biochemistry, even including psychology. I would not be so bold as to say that the link is in anyway definitive, but it makes for some interesting reading.

With autism in mind, vitamin D has also received more than passing mention. As with all dietary components, the possible influence of unusual eating habits and patterns attributed to many cases of autism, would perhaps predispose some people on the autism spectrum to a reduced intake of dietary-derived vitamin D. The research in this area does seem to corroborate this suggestion. One of the bigger names in all things vitamin D, Dr John Cannell, wrote an interesting paper about vitamin D and autism not so long ago (here). Putting the universality of the vitamin D-autism hypothesis to one side, there are some interesting points raised in his paper which are beginning to be borne out by the accumulated research in this area. In particular are the various research on autism in specific ethnic populations such as the Somali community, and the evidence put forward for some increase in autism prevalence in such groups when resident in more Northern climes. I would reiterate the old 'correlation does not imply causation' adage at this point also.

Another interesting area of research relates to the various work on the gastrointestinal (GI) co-morbidities noted alongside some cases of autism, and whether malabsorption as a result of coeliac disease or hyperpermeability of the gut might play a hand in hypovitaminosis D as has been suggested elsewhere. This research published on Egyptian children might be relevant to this side of the hypothesis given that I am sure that sunshine is at a premium in the land of the Pharaohs. Finally, although there is no contemporary epidemiological evidence to speak of, autism does not seem to be protective against the development of rickets as witnessed by this study (one of the study authors being also involved in this paper on iron deficiency and autism) and this study.

Taking into account the evidence currently available, I don't think that we can say that autism, or any one condition, has a monopoly on low levels of vitamin D. Many people from many different ethnic, geographic and symptomatic groups seem to be on the low side of what would be considered to be 'adequate' levels of vitamin D. There is also the 'chicken and egg' situation in terms of whether vitamin D levels are 'causative' of anything (outside of rickets or other classically related conditions) as complicated as autism or schizophrenia, etc. or just symptomatic of some other underlying mechanism or dysfunction. I will leave you to make your decision on this issue. Finally, vitamin D might be only one part of any association as can be seen by this editorial on how UVB sunlight might also have some other interesting effects.

To finish, this Sassenach wonders how many miles would you walk?