Aside from the experience in his ward, mostly the other evidence seems to be the correlation between winter and the spread of influenza. There may be other caus

Aside from the experience in his ward, mostly the other evidence seems to be the correlation between winter and the spread of influenza. There may be other causes for that correlation besides vitamin D (or they might all be contributing factors), such as: -People spend more time indoors, closer to other people. If the virus is airborne or spread through human contact, transmission rates would naturally go up in the winter. -People travel during the holidays so the virus has more opportunity to spread around: more people trapped in airplanes with sick people, and more sick people moving viruses from point A to point B. That said, I'd like to see more evidence and discussion of whether taking vitamin D supplements are worthwhile, I suspect they are but am not convinced entirely by this article.