However, a recent study holds some interesting information for us on this front. A meta-analysis of 25 high-quality studies was undertaken and published in the British Medical Journal recently. It found that a Vitamin D supplement was a safe and effective way to minimise risk of acute respiratory infections .
The study took in data from almost 11,000 participants across the 25 studies. All studies included in the meta-analysis and systemic review were randomised, double blind, placebo controlled studies that had been approved by a research ethics committee. The BBC reported that:
“Overall, the study said one person would be spared infection for every 33 taking vitamin D supplements. That is more effective than flu vaccination, which needs to treat 40 to prevent one case, although flu is far more serious than the common cold .”
The study found that :
Professor Adrian Martineau, one of the study’s authors, remarked that, “Assuming a UK population of 65 million, and that 70% have at least one acute respiratory infection each year, then daily or weekly vitamin D supplements will mean 3.25 million fewer people would get at least one acute respiratory infection a year .”
That said, it is possible that the UK has higher numbers of vitamin D deficient persons simply due to the weather. Still, the research holds some interesting numbers indeed.
The study also found regular (daily or weekly) doses to be more effective than monthly super-doses . Although it focused on acute respiratory infections, the work echoed research done by Urashima et al which found Vitamin D supplements taken in winter may reduce the incidence of Influenza A in school children .
These findings appear to vindicate Dr John Cannell, founder of the Vitamin D Council, who introduced the idea that a Vitamin D deficiency may actually be an underlying cause of influenza. He proposed this idea back in 2006, and followed it up with a study in the Virology Journal in 2008. He said that:
“The findings of our study support an important role for vitamin D in prevention of common respiratory infections, such as colds and the flu. Individuals with common lung diseases, such as asthma or emphysema, may be particularly susceptible to respiratory infections from vitamin D deficiency .”
Of course, a study like this is not without its detractors, with some questioning the reliability of the data. However, one thing is without doubt: the so-called sunshine vitamin has a role beyond brain and bone health. It may just hold some protective properties worth thinking about.
 Martineau Adrian R, Jolliffe David A, Hooper Richard L, Greenberg Lauren, Aloia John F, Bergman Peter et al. Vitamin D supplementation to prevent acute respiratory tract infections: systematic review and meta-analysis of individual participant data BMJ 2017; 356 :i6583 http://www.bmj.com/content/356/bmj.i6583
 Gallagher, J (2017), “Vitamin D pills ‘could stop colds or flu,” BBC, http://www.bbc.com/news/health-38988982, retrieved 6 March 2017
 MacMillan, A (2017), “Here’s how to avoid catching colds and the flu,” Time Magazine, http://time.com/4672626/vitamin-d-cold-flu/ retrieved 6 March 2017
 Urashima M, Segawa T, Okazaki M, Kurihara M, Wada Y and Ida H (2010), “Randomized trial of vitamin D supplementation to prevent seasonal influenza A in schoolchildren,” American Journal of Clinical Nutrition, May 2010, Vol. 91 No.5 pp 1255-1260, http://ajcn.nutrition.org/content/91/5/1255.abstract?maxtoshow&hits=10&RESULTFORMAT=1&andorexacttitle=and&andorexacttitleabs=and&andorexactfulltext=and&searchid=1&FIRSTINDEX=0&sortspec=relevance&resourcetype=HWCIT
 Mercola, (2017), Vitamin D is more effective than flu vaccine, study says,” Dr. Mercola, http://articles.mercola.com/sites/articles/archive/2017/02/27/vitamin-d-better-than-flu-vaccine.aspx retrieved 6 March 2017