The most recent study on vitamin D and the flu<http://www.ajcn.org/cgi/rapidpdf/ajcn.2009.29094v1>, published in the American Journal of Clinical Nutrition (March, 2010), shows that vitamin D reduces the risks of flu and asthma attacks significantly. Researchers from Japan conducted a double-blind, randomized, placebo-controlled trial involving over 300 school children aged 6 to 15 years old. Eight physicians were involved in diagnosing the flu among these children, spread across 12 hospitals. They randomly allocated half the children to take 1200 IU per day of vitamin D-3 and the other half to take a placebo. The children took the supplements from the beginning of December, 2008 to the end of March, 2009.
About ten percent (10.8%) of children in the vitamin D group developed Influenza A, whereas 18.6% developed the illness among the placebo group. This suggests that vitamin D cut the risk of developing the flu by nearly half. Many of the children in both groups began taking additional vitamin D supplements after the trial was underway, however. Excluding these children from the analysis showed that vitamin D cut the risk of flu by 64 percent! In a remarkable secondary finding, vitamin D appeared to nearly obliterate the risk of asthma attacks. Children who were previously diagnosed with asthma were six times more likely to have an asthma attack during the course of the study if they were in the placebo group. This suggests that vitamin D supplementation reduced the risk of getting an asthma attack by 83 percent. The authors cited previous work showing that the drugs marketed as Relenza and Tamiflu only reduce the incidence of flu by eight percent. The authors of the paper also cited other studies showing that probiotics (good bacteria) and a preparation of echinacea, propolis, and vitamin C helped reduce the risk of flu. Note: Another study published earlier showed vitamin D also reduced the risk of cold and suggested that the higher incidence of cold in winter might be, at least in part, due to deficiency of vitamin D in winter as people had less exposure to sun shine in those months. The darker and older is your skin, the more sun exposure you need to produce enough vitamin D. No safe amount of sun shine will produce enough vitamin D for some people—especially older people. Vitamin D deficiency is wide spread in the US, Europe and many other parts of the world. Many experts believe that the daily intake of Recommended Daily Allowance (RDA) of 400 IU of vitamin D is not enough for most people. It should rather be between 1000 and 2000 IU per day.
