High Levels of Vitamin D Protect Against Common Cold and Flu

A century ago, spending time in the sun -- a great way to make vitamin D -- was one of the main treatments for tuberculosis. Three years ago, researchers identified the mechanism -- vitamin D is needed to make a potent infection fighting immune compound called cathelicidin. Now researchers have found that the benefits of vitamin D may extend to protection against the common cold and influenza.

Adit A. Ginde, MD, of the Children's Hospital, Boston, and his colleagues analyzed blood levels of vitamin D and the risk of upper respiratory tract infections (URTIs) in 18,883 men, women, and teenagers. Twenty-four percent of people with very low vitamin D levels had reported recent URTIs, and 20 percent of those with marginal levels had URTIs. Seventeen percent of those with normal vitamin D levels reported URTIs.

Overall, low levels of vitamin D were associated with a 36 percent greater risk of URTIs. However, people with chronic obstructive lung disease and low vitamin D levels had twice the risk of developing URTIs. In addition, people with asthma and low vitamin D levels had almost a six-time greater risk of URTIs.

Ginde noted that exposure to sunlight is the primary determinant of vitamin D in people. "Vitamin D supplementation may reduce the incidence of URTI and exacerbations of respiratory tract diseases," he wrote.

Reference: Ginde AA, Mansbach JM, Camargo CA. Association between serum 25-hydroxyvitamin D level and upper respiratory tract infection in the third national health and nutrition examination survey. Archives of Internal Medicine, 2009;169:384-390.