On the radio this morning I heard a news story about a scientific study claiming that vitamin D supplements can protect you from the common cold. Upon logging in to Twitter I found numerous headlines along the same theme and so I decided to do some digging and see how realistic these claims were.
The headline is based on a meta-analysis of studies looking at vitamin D in relation to respiratory tract infections (basically any infection of the sinuses, airways or lungs). A meta-analysis is a statistical analysis of data gathered from multiple scientific studies. The idea is that results from similar scientific experiments can be pooled and compared to learn more about the subject of the experiments (in this case vitamin D and respiratory tract infections).
The analysis was published in the British Medical Journal on the 15th of February and has been a hot topic of discussion ever since. The eligibility criteria for which scientific studies to include in the analysis were:
“Randomised, double blind, placebo controlled trials of supplementation with vitamin D… if data on incidence of acute respiratory tract infection were collected.”
In plain English that means a trial where there were two groups; one receiving vitamin D and one receiving a placebo (e.g. a tablet with no effect such as a sugar pill). People were assigned to these groups randomly (usually by a computer program) and neither the participants nor the people carrying out the study knew which group was which (double blind).
The main conclusion of this review was that vitamin D supplements do help protect against respiratory tract infections but it’s people who are vitamin D deficient that benefit the most. The authors also concluded that the use of vitamin D was safe and that adverse reactions were rare across all of the studies included.
Although this is the largest review of its kind and the results look promising, the design of the studies included vary greatly on important factors such as how much vitamin D was taken by the participants and how often. There may also be differences between what classes as a respiratory tract infection in each study so statistically the data may be sound but clinical trials have yet to consistently show any benefit to taking vitamin D.
Overall, as enticing as the headline sounds and as important as this review is, I wouldn’t recommend stocking up on vitamin D tablets any time soon.
Here’s the original paper if you want a read: http://www.bmj.com/content/356/bmj.i6583