The randomized trial led by Mitsuyoshi Urashima from Jikei University School of Medicine Minato-ku in Tokyo, Japan and colleagues shows that schoolchildren who took vitamin D3 supplements were 64 percent less likely to contract seasonal influenza A viral infection, compared with those who did not take the supplements.
The United States Centers for Disease Control and Prevention has recently announced that influenza vaccine for this reason is about 65% effective. Considering that trials of influenza vaccine are often times to determine the efficacy of a vaccine based on its effect on some biomarkers, but not clinical outcomes, so the real efficacy for influenza vaccine may be lower.
The CDC claims that influenza vaccine is the best preventative against influenza. But the study suggests that taking vitamin D supplements may be at least as effective as influenza vaccine in preventing influenza viral infections.
The randomized, double-blind, placebo-controlled trial conducted between Dec 2008 and March 2009 was intended to examine the effect of vitamin D supplementation in a dose of 1,200 International Units per day on the incidence of seasonal influenza A in schoolchildren. T he primary outcome was diagnosis of influenza A based on the influenza antigen testing.
The effectiveness was striking: Influenza A viral infection was diagnosed in 18 of 167 (10.8%) children taking vitamin D3 supplements, compared with 31 of 167 (18.6%) children who did not take the supplement.
Among children who did not take other vitamin D supplements prior to the trial, those who took vitamin D3 supplements during the trial were 64 percent less likely to acquire influenza A, compared with children who did not take supplements during the trial.
The results were similar among children who started nursery school after age 3 years, that is, taking vitamin D3 supplements reduced the risk of influenza A viral infection by 64 percent, compared with controls.
Among children with asthma diagnosed prior to the trial, asthma attacks were reduced by 83 percent in those who took vitamin D3 supplements, compared with those who did not take the supplements.
The researchers concluded "Vitamin D3 supplementation during the winter may reduce the incidence of influenza A, especially in specific subgroups of schoolchildren."
A few more trials conducted after the Japanese trial also demonstrated that vitamin D supplementation can not only reduce risk of influenza, but also other infections.
Dr Peter Bergman fromKarolinska Institutet in Stockholm, Sweden and colleagues conducted a study of 140 patients with frequent respiratory tract infections and found those who took 4000 IU per day were less likely to contract respiratory tract infections during the one-year supplementation trial. The study was published in BMJ Open.
The results from the Japanese trial and others can be explained by the fact that vitamin D promotes the production of antibacterial peptides which are involved in innate immunity against various infections, according to a study in Nature. Observational studies have shown people with low serum vitamin D were at higher risk for influenza and other viral infections.
Dr. John Cannell, director of Vitamin D Council, a non-profit organization, suggests that adults should take 5000 IU of vitamin D per day and the current recommended allowance is lower than needed.
The trials are good news for those who do not use influenza vaccine. But when you decide to buy vitamin D supplements, make sure that the supplements do not contain unhealthy or potentially harmful ingredients. T he best vitamin D supplement we have seen on the market is vitamin D drops.
