By David Liu, PHD

Thursday Dec 13, 2012 (foodconsumer.org) -- A review article recently published in The Journal of Steroid Biochemistry and Molecular Biology reminds readers that vitamin D deficiency, a condition that is more commonly seen in the Winter, can increase risk of both upper and lower respiratory tract infections.

David A. Jolliffe from Queen Mary University of London in London, UK and colleagues found that evidence is strong from 39 studies including four cross-sectional studies, eight case-control studies, 13 cohort studies and 14 clinical trial studies indicating that vitamin D deficiency was associated with increased risk for upper and lower respiratory tract infections. 

Vitamin D has been known to be involved in innate immunity against bacterial and viral infections, according to many studies including some published in prestigious scientific journals like Nature.

Observational studies are consistent and an overwhelmingly majority of the studies showed statically significant association between vitamin D insufficiency or deficiency and elevated risk of upper and lower respiratory tract infections, according to the reviewers.

Clinical trials are inconsistent, which is understandable because they used different doses and different vitamin D statuses at baseline. 

Dr. John Cannell, Director of Vitamin D Council, reported in his newsletter, said two physicians reported to him that they observed that relatively high doses of vitamin D (in thousands of IUs) effectively protected against H1N1 virus.

In the Winter, mild viral infections are common.  While the government, hospitals and pharmacies, even Walmart promote flu vaccine, studies have shown vitamin D, vitamin C, zinc supplements can all help fight viral infections like flu.