Are you getting enough vitamin D? The answer may lie in how often you catch a cold. A February 23 2009 study published in the Archives of Internal Medicine
shows a link between low levels of vitamin D and increased respiratory infection risk from colds and flu.
In the largest study to date examining vitamin D levels and respiratory infection rates, researchers found that people with higher levels of vitamin D in the blood were less likely to experience colds than those with deficiencies. Additionally, the risk of respiratory infections and colds appeared to increase with falling vitamin D levels.
"People think that if they have a good, balanced diet that they will get enough vitamin D, and that's actually not true," said Dr. Michal Melamed, an assistant professor at Albert Einstein College of Medicine in New York. "Unless you eat a lot of fish and drink a lot of milk, you can't get enough vitamin D from diet."
Dr. Adit Ginde, an assistant professor of surgery at the University of Colorado's Denver School of Medicine, and his team from Harvard Medical School and Children's Hospital Boston reviewed data from the Third National Health and Nutrition Examination Survey. Information collected between 1988 and 1994 from about 19,000 Americans aged 12 and up was analyzed for results.
Over half of the people in the study had vitamin D levels that were less-than-optimal for protection against respiratory infections. Those with the lowest levels (below 10 nanograms per milliliter) were most likely to have experienced cold recently. Asthmatics were up to six times more likely to experience colds when vitamin D levels were low.
"We still need to do the clinical trials that we already have planned to definitely say whether supplementation with vitamin D would actually reduce the risk we found," Ginde said. "But I think we can say that most Americans probably do need more vitamin D for its effects on bone health, as well as for its general benefits with respect to the immune system."