The link between the sunshine vitamin and winter health

The fact that people’s vitamin D levels tend to decrease in the winter and flu incidence tends to increase has led researchers to question whether the two might be related. This study explored the link between vitamin D and the most common type of seasonal flu (influenza A). Four hundred and thirty schoolchildren between 6 and 15 years old were randomly assigned to take vitamin D supplements (in the form of vitamin D3; 1,200 IU per day) or a placebo starting in December and ending in late March.

It turns out that the children who took vitamin D supplements had a slightly lower incidence of flu compared with those who did not: 10.8% of the children in the vitamin D3 group got the flu, compared with 18.6% in the placebo group (a 42% risk reduction).

So can the sunshine vitamin reduce flu risk? The study authors comment, “This study suggests that vitamin D3 supplementation during the winter may reduce the incidence of influenza A, especially in specific subgroups of schoolchildren.” But further research is needed to determine if vitamin D supplements help prevent flu, and to determine what doses and duration of treatment are optimal.

Expanding awareness of vitamin D’s role in health

We are learning more and more about how optimal vitamin D levels are essential for good health, preventing disease, and now perhaps even preventing infections (such as the flu). This latest study is just another reason to make sure your vitamin D levels are healthy:

• Talk with a doctor. Talk with a doctor or pediatrician about the vitamin D requirements for you and your child and whether your levels should be checked, especially if you live in northern latitudes with lots of cloud cover or you and your child don’t spend much time outdoors. People who live in less sunny climates or who suffer from chronic disease may particularly be at risk for low vitamin D levels.
• Follow a doctor’s advice about supplementation. If vitamin D levels are low a doctor may recommend vitamin D supplements for you or your child. It is important to take supplements under the care and advice of a physician—you want to optimize the benefit of a supplement and minimize the potential for harm, which may occur from taking too much of a vitamin or from interactions between supplements and/or medications.

(Am J Clin Nutr doi:10.3945/ajcn.2009.29094)