Vitamin D3 Gives Mixed Results for Preventing Flu in Schoolchildren

Vitamin D has been the subject of great research attention over the last five years. Among it’s many potential health benefits is enhancement of immune system function, leading some people to believe that vitamin D supplementation might be helpful in preventing seasonal infectious conditions like the flu.

Researchers in Japan conducted a randomized, double-blind, placebo-controlled trial to investigate the relationship between vitamin D3 and seasonal influenza in children. Vitamin D3 supplementation was not clearly shown to reduce overall incidence of influenza, though it did reduce the incidence of influenza A infection (level 2 [mid-level] evidence).

In the trial, 430 schoolchildren aged 6-15 years were randomized to receive either vitamin D3, 600 IU twice daily for a total of 1,200 IU/d, or placebo from December 2008 through March 2009. A total of 334 children (78%) were included in the final analysis, with 96 children (22%) being lost to follow-up. Presence of influenza was confirmed by rapid antigen testing.

In comparing the vitamin D3 group versus the placebo group, influenza A was confirmed in 10.8% versus 18.6%, respectively  (p = 0.04, NNT 13). While influenza B was confirmed in 23.3% versus 16.8% (p = 0.13). Overall, there was no significant change in total flu incidence between the supplemented and unsupplemented kids (Urashima M, et al. Am J Clin Nutr. 2010; 91(5): 1255-60).

Interestingly, among the children previously diagnosed with asthma, vitamin D supplementation reduced the incidence of asthma attacks, which occurred in 1.2% in the vitamin D3 group and 7.2% in the placebo group (p = 0.006, NNT 17).

Seasonal influenza epidemic in the United States typically occurs annually from late fall to early spring, a period during which sun exposure is limited and a large number of people living in northern latitudes become vitamin D deficient.

This trial explores vitamin D as possible prophylactic against seasonal influenza. The data show that vitamin D3, at a dose of 1,200 IU/d, did reduce the risk of getting influenza A, but it was also associated with an increase in influenza B, giving no net decrease in the total rate of influenza or influenza-like illness in these school-aged children.

This article was adapted from DynaMed, published by EBSCO Publishing ( DynaMed is a commercial-free clinical reference tool created by physicians for physicians and other healthcare professionals for use at the point-of-care. Offering clinically organized summaries for more than 3,200 topics, DynaMed is updated daily, and monitors the content of over 500 medical journals and systematic evidence review databases. New data are evaluated using DynaMed’s 7-Step Evidence-Based Methodology, then integrated with existing content, and overall conclusions are revised as appropriate, representing a synthesis of the best available evidence.
For more information on vitamin D3, see the Influenza in children topic in DynaMed.

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