Vitamin D, long known for its beneficial effect on bones, has now been found to help prevent colds and flu. In fact, some doctors are going so far as to recommend high doses to help stave off respiratory infections. It seems that vitamin D is very good at boosting your immune system and could literally fight off influenza in much the same way as the flu shot does.
Until recently, scientists have blamed the rise in flu cases during winter on an increased tendency to congregate inside in groups. Low humidity has also been blamed, as viruses are said to survive longer in drier air. But the real culprit responsible for the winter cold and flu season may be vitamin-D deficiency.
It seems that, in the winter months, the sun is not strong enough to trigger vitamin-D synthesis in our skin, resulting in lower vitamin-D absorption.
To test this theory of vitamin-D deficiency causing an increased risk for getting the flu, researchers at the Jikei University School of Medicine in Tokyo, Japan, recruited 167 school children for a clinical trial. From December 2008 through March 2009, the research team conducted a randomized, double-blind, placebo-controlled trial comparing vitamin D(3) supplements with placebo.
The researchers found that Influenza A occurred in 18 of 167 (10.8%) children in the vitamin D(3) group, compared with 31 of 167 (18.6%) children in the placebo group (an almost two-fold increase). The researchers also found that, for children with a previous diagnosis of asthma, asthma attacks as a secondary outcome occurred in two children receiving vitamin D(3), compared with 12 children in the placebo group — a significant increase!
The research team concluded that vitamin-D(3) supplementation during the winter may reduce the incidence of influenza A.
The best source of vitamin D is the sun, of course. UV rays from the sun trigger vitamin-D synthesis in your skin. Ten to 15 minutes of sun exposure at least two times a week to your face, arms, hands or back is enough to give you a healthy dose of vitamin D. Keep in mind, however, that long winters and sun avoidance in the summer mean that you may not be getting enough vitamin D this way.
One other note: vitamin-D synthesis is less efficient in people with darker skin, and African Americans are at higher risk of deficiency than whites. Overweight adults can also be at risk because vitamin D is stored in body fat. The more vitamin D that gets stored into fat tissue, the less active vitamin there is in the blood.
Here are some food sources of vitamin D:
–Cod liver oil (the best source)
Milk, breakfast cereals, and orange juice fortified with vitamin D are also good food sources. If you wish to look into vitamin-D supplements, check with your doctor first on what dosage is best for your particular case.