Nutrition for winter: vitamin D

not enough sunlight for vitamin D production

Can vitamin D prevent the flu?  IOM politics aside, some health researchers suspect a connection.  In 2008, a discussion of vitamin D’s possible flu connection in the Journal of Virology posed several questions about flu, such as why is flu seasonal (in winter) and why do flu epidemics end abruptly in spring.  Vitamin D is known to enhance natural antibiotic activity in the body.  Could there be a connection?  Before supplements were available, and before anyone even knew about vitamin D, humans got their D the natural way, from sunlight.  A narrow band of intense rays stimulate vitamin D production in skin cells.  This process does not work in winter at more northern latitudes.  Could D deficiency, worsening through autumn into winter, increase susceptibility to flu, due to a negative effect on immunity?

The theories are fascinating, but is there data to back them up?  A review of relevant studies, compiled in 2009, looked at a few vitamin D-flu interventions.  The studies were not conclusive, but the review authors noted that the trends showed vitamin D supplementation improving flu and upper respiratory infection rates and outcomes.  Their recommendation was for more studies, with better controls and larger numbers of subjects.  Since that review was published, a study done at Yale looked at blood vitamin D levels and incidence of flu.  Findings: subjects with higher blood levels of vitamin D (38 ng/ml or higher) were far less likely to have an upper respiratory infection during the winter study period.  More studies are in the works, and hopefully results will clarify the key question: what blood level of vitamin D is linked to significant reduction in flu risk?

Well, you could ask the Chicago Blackhawks hockey team.  After seasons of poor performance, the players were checked for vitamin D status, and started on supplements by the team physician prior to last year’s season.  URI’s were drastically reduced.  Oh and they unexpectedly qualified for the Stanley Cup tournament, and went on to win the Stanley Cup.  Well, we probably can’t attribute all of their success to a vitamin, but athletes who are not run down with illness are more likely to play better.  Some other hockey teams, amateur and professional, are following the Blackhawks example this season.

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