Feb. 23, 2009 -- A walk in the sun may be better than popping a vitamin C tablet for boosting your chances of preventing the common cold or flu.

A new study adds to mounting evidence that vitamin C may have been stealing the spotlight all these years from the real cold fighter, vitamin D.

The study, the largest to date on the link between vitamin D and common respiratory infections, shows that people with the lowest vitamin D levels report having significantly more cases of cold and flu than those with higher levels. Vitamin D is produced by the body in response to sunlight and is also found in fortified foods such as milk.

Researchers say that although vitamin C has been used for the prevention of common colds and other respiratory infections for decades, there is little scientific evidence to support its effectiveness. However, several recent studies have suggested that vitamin D, better known for its role in building strong bones, may also play a critical role in immune system function.

"The findings of our study support an important role for vitamin D in prevention of common respiratory infections, such as colds and the flu," says researcher Adit Ginde, MD, MPH, of the University of Colorado, Denver, Division of Emergency Medicine, in a news release. "Individuals with common lung diseases, such as asthma or emphysema, may be particularly susceptible to respiratory infections from vitamin D deficiency."