Vitamin D was found to be even more effective when the comparison left out children who were already given extra vitamin D by their parents, outside the trial. Taking the sunshine vitamin was then shown to reduce the risk of flu to a third of what it would otherwise be.
The Japanese scientists, writing in the American Journal of Clinical Nutrition, say that the anti-viral drugs zanamivir and oseltamivir reduce risk of flu infection by 8 per cent in children who have been exposed to infection, compared with a 50 per cent or greater reduction with vitamin D.
Anti-virals are also too expensive, and possibly too toxic, to be given to the population as a whole whereas vitamin D has additional benefits. The sunshine vitamin not only prevents bone fractures but is also believed to reduce risks of cancer, heart disease, diabetes and other illness, including various bacterial as well as viral infections.
