Close Encounters of the Nutritional Kind
Number 2 – You are Vitamin D deficient – or are you?
OK, I know I said these would be weekly but given all of the media attention yesterday on Vitamin D and the number of media requests I received to speak about it, I thought I would pen a few thoughts about my understanding of Vitamin D, the research I am doing on it and what we do in elite sport.
Yesterday there was a large meta-analysis discussed on many UK media outlets that has shown correcting vitamin D deficiencies seems to offer protection against respiratory tract infections (for those confused a meta-analysis is where someone takes lots of already published research trials and combines the results into one really big study). There is also previous data in athletes that has shown vitamin D may predict your chances of getting a winter cold. No doubt this media attention will result in everyone running out today to buy vitamin D supplements. But is there more to the vitamin D story than is often presented? In my opinion – Yes.
Figure above – One of my lecture slides showing research from Mike Gleeson’s group that low vitamin D concentrations increases risk of infections.
Are we vitamin D deficient – Maybe – but maybe not. Vitamin D, unlike other vitamins, is mainly synthesised from sunlight exposure, so for those of us living in northerly latitudes the chances are our sunlight is limited. It also should not be called a vitamin – it is actually a pro hormone meaning it has many effects on many target tissues. Unfortunately, only a few food items contain vitamin D (small amount in eggs, oily fish and certain mushrooms) and multi-vitamin supplements have such a low amount in them that they would not correct a deficiency if we had one. Our group as well as others have reported that a consequence of inadequate sunlight exposure is that many athletes when tested appear to be vitamin D deficient (I class <75nmol/L deficient). HOWEVER, like all things the story gets much more complicated.
Figure above – vitamin D status of athletes. Lots of athletes do present with low Vitamin D concentrations. But have I (and the others) been measuring the right thing!
The Black Athlete Paradox
We know that black athletes (and non-athletes) have lower vitamin D concentrations than white athletes. This may lead us to think that this group MUST immediately take vitamin D to correct this deficiency but let’s think about this logically for a second. What are the consequences of low vitamin D? Weak bones, impaired muscle function, more coughs and colds etc. Now, think about some of the black athletes I (or you) may work with – they often have the strongest bones of all the squad, certainly not lacking muscle function (we wouldn’t say Usain Bolt was slow) and not the first ones to get a cold when one goes around the squad. We have a paradox and for too many years’ people have not asked why.
We believe the reason for this paradox is that we have been measuring the wrong thing to assess deficiencies. Please stay with me. When we get a vitamin D test you will normally receive a test for 25(OH)D, the major form of vitamin D in the circulation. For many people this is a good test but there is now research to show that darker skinned people whilst having low 25(OH)D actually have more than sufficient “bioavaialable” 25(OH)D. So more of their vitamin D is free to perform its role where in whites it is more tightly bound to its binding protein and therefore more is needed to work. The end result is that the test we are using to assess deficiency is in fact not the correct test for a large proportion of the population. And it is this test that the meta-analysis etc are based upon.
Add to this we have recently shown that, contrary to popular belief, you can have too much vitamin D supplementation. In this study we gave 10,000 iU per day to athletes, a dose that has been advised by many experts for several years. Almost as soon as we gave the supplement the body tried to break it down and worryingly stopped converting vitamin D to its active metabolite (1-25OHD). The consequences being that we can be worse than before we started supplementing.
I said it was more complicated than first presented. Let me try and simplify this and explain what I do with the athletes I work with daily?
- If I am working with a mixed race squad then I see if I can get bioavailable vitamin D tested. If less than 5 nmol/L I would deem this deficient and look to correct.
- If I am working with a white athlete I will see if I can get 25(OH)D tested. If <75 nmol/L I would deem deficient and look to correct.
- If I can test for these things I will identify the deficient athletes and supplement accordingly. EFSA (European Food Standards Agency) and the US Institute of Medicine both suggest 4,000 iU per day as the upper limit. This is the maximium dose I will use if an athletes fits into my deficient category. I do not like large blous doses for many reasons but just trust me this is not as effective as daily supplementation.
- If I cannot test the right thing and I suspect we may be low (living in the UK in winter) I supplement anyway with 2000 iU per day through the winter months and then advise sensible sun exposure in the summer. I currently use Health Span Elite https://wwhealthspan.co.uk/elite/elite-high-strength-vitamin-d3 as they are batch tested with informed sport. If you get 1000 iU tablets it is easy to give the doses I suggest.
So basically, if I cannot test the right thing I don’t even bother trying to test, its just a waste of time and money. I just presume a deficiency and give a small dose that will correct if there is a problem but will stay well away from the unsafe zones. There is little point measuring vitamin D in black athletes if we cannot get bioavaialable vitamin D.
Hopefully that has cleared up some confusion on vitamin D.
Until the next Close Encounter of the Nutritional Kind