Vitamin D supplementation did not prevent influenza-like illness as diagnosed retrospectively by questionnaires in subjects participating in randomized clinical trials

Scand J Infect Dis. 2012 Feb;44(2):126-32. doi: 10.3109/00365548.2011.621446. Epub 2011 Oct 25.


Background: Vitamin D deficiency has been associated with a number of diseases, including influenza. Whether or not this reflects a causal relationship is unknown. We therefore wanted to examine if supplementation with vitamin D would affect the incidence and severity of influenza-like disease.

Methods: Questionnaires on influenza were sent to subjects participating in ongoing placebo-controlled intervention studies with vitamin D supplementation, up until the end of April 2010.

Results: Five hundred and sixty-nine subjects from 10 different clinical trials were included in the study, of whom 289 were randomized to receive vitamin D (1111-6800 IU/day) and 280 to receive placebo. Influenza-like disease during the previous fall/winter was reported in 38 subjects in the vitamin D group and 42 in the placebo group (non-significant), of whom 25 and 26 subjects, respectively, fulfilled our clinical criteria for influenza. In these latter subjects, the duration of illness was significantly longer among those in the vitamin D group than among those in the placebo group (median 7 (range 2-60) days vs median 4 (range 2-18) days; p = 0.007). However, this difference was not statistically significant if all 38 (vitamin D) and 42 (placebo) subjects who reported symptoms were included.

Conclusion: Our results do not support the hypothesis that high doses of vitamin D supplementation will have a pronounced effect on influenza-like disease in populations not targeted for high influenza risk.

Publication types

  • Randomized Controlled Trial
  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Data Collection
  • Dietary Supplements
  • Humans
  • Influenza A Virus, H1N1 Subtype
  • Influenza, Human / prevention & control*
  • Retrospective Studies
  • Surveys and Questionnaires
  • Vitamin D / pharmacology*


  • Vitamin D