Although some data have suggested a possible inverse association between serum vitamin D levels and the incidence of upper respiratory tract infections (colds), participants in a randomized controlled trial who received a monthly dose of 100,000 IUs of vitamin D3 did not have a significantly reduced incidence or severity of colds, according to a study in the October 3 issue of JAMA. The association of vitamin D insufficiency and susceptibility to viral respiratory tract infections has been unclear, according to background information in the article.
