Written by Jessica Patella, ND.
Vitamin D has been making headlines on various health topics, but can it prevent the flu in schoolchildren? Recent research indicates that supplementing vitamin D3 during the winter can prevent influenza A (1). Most vitamin D comes from spending time in the sun. During the winter months, when flu rates are the highest, blood levels of vitamin D are usually decreased by 50% compared to the summer months (2).
In a recent study, 430 children aged 6-15 years received either a placebo or 1200 IU of vitamin D3 per day. Of the 430 children that began the study, only 334 were followed until the end of the study and 96% of those took the supplement as directed.
Eighteen of the 167 (10.8%) children receiving vitamin D3 were diagnosed with influenza A, compared with 31 of the 167 (18.6%) children receiving the placebo (1). Physicians used a rapid influenza diagnostic test with a nasopharyngeal swab to diagnose the children with influenza. This test confirmed a diagnosis and identified the subtype of influenza, type A or type B (1).
Vitamin D supplementation did not significantly help children that had flu-like symptoms that tested negative for influenza with a nasopharyngeal swab or children that tested positive for influenza subtype B (1). This difference could be due to the fact that influenza A and influenza B secrete different cytokines (3). Cytokines are substances secreted by cells to help them communicate.
During this study, the researchers also discovered children that were not taking vitamin D prior to the study and who started nursery school at the age of 3 years or older had a more significant reduction in influenza A (1). Of these children, only 8 of 107 (7.5%) taking vitamin D3 were diagnosed with influenza A, compared to 20 of 117 (20.5%) taking placebo (1).
Research shows it takes about 3 months to reach a constant level of vitamin D in the blood from supplementation (4). Therefore, starting supplementation in December might be too late. However, vitamin D3 significantly reduced the incidence of influenza A within 60 days in this study (1).
The study was randomized and double-bind, meaning neither the physicians nor patients knew if the patient was receiving the placebo or vitamin D and the patient was randomly assigned to either the placebo or vitamin D group.
In conclusion, daily supplementation with 1200 IU of vitamin D3 in school aged children, during the winter months, showed a significant preventive effect against influenza A, although no significant difference was observed for influenza B (1).
Source: Urashima, Mitsuyoshi, et al. “Randomized trial of vitamin D supplementation to prevent seasonal influenza A in schoolchildren.” The American journal of clinical nutrition 91.5 (2010): 1255-1260.
© 2010 American Society for Nutrition
Posted May 6, 2010.
References:
- Urashima, et al. Randomized trial of vitamin D supplementation to prevent seasonal influenza A in schoolchildren. Am J Clin Nutr. Doi: 10.3945/ajcn.2009.29094.
- Cannell JJ, et al. On the epidemiology of influenza. Virol J 2008; 5:29.
- Sato, et al. Differences in serum cytokine levels between influenza virus A and B infections in children. Cytokin 2009; 47:65-8.
- Vieth, et al. Efficacy and safety of vitamin D3 intake exceeding the lowest observed adverse effect level. Am J Clin Nutr 2001; 73: 288-94.
