Back in February I wrote a post that was largely focused on my experience of supplementing with vitamin D, and specifically the fact that I had not had a single infection (e.g. cold or flu) since starting supplementation. I still, by the way, have not had an infection. Not even a hint of one. This might all be coincidental, but others (some of whom have commented on the site) do seem to have similar experiences. And given that there are plausible mechanisms through which vitamin D can afford relative protection from infection, there does seem to be mounting evidence that vitamin D can indeed help keep us infection-free.
This week saw the publication of a study which adds further support to the idea that vitamin D can help the body ward off infection. In a study, published in the American Journal of Clinical Nutrition, Japanese schoolchildren aged 6-15 years were treated from December through to the end of March with vitamin D (1200 IU per day) or placebo . The outcome assessed was infection with the viruses influenza A and B (the two most clinically important of the three main types of influenza virus). As an aside, influenza A includes the H1N1 strain that last year was responsible for the ‘pandemic’ alerts of last year.
Whether a child had succumbed to influenza over the course of the study was tested microbiologically using swabs from the nose/throat.
Vitamin D supplementation was not associated with a reduced risk of infection with influenza B. However, for influenza A, the results were positive, with vitamin D reduces risk of infection by 42 per cent overall. The benefits were even more dramatic in children who had not been previously supplementing with vitamin D: in this group of children, risk reduction was 64 per cent.
Interestingly, in children with a history of asthma, there was no reduction in risk of flu virus infection. However, those taking vitamin D were at very significantly reduced risk of having an asthma attack.
What we have here is a placebo-controlled study which demonstrates that vitamin D supplementation has the power to protect against flu. This study, to my mind anyway, provides good scientific support for the anecdotal experiences of those, including myself, who have found that vitamin D supplementation has afforded protection against viral infection.
1. Urashima M, et al. Randomized trial of vitamin D supplementation to prevent seasonal influenza A in schoolchildren. Am J Clin Nutr 10th March 2010 [epub before print publication]