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."
Vitamin D vs. Colds
Although circumstantial evidence has implicated wintertime low levels of vitamin D to the seasonal increases in colds and flu, some smaller studies have also hinted at a link between low vitamin D level and a higher risk of respiratory infections.
In this study, published in the Archives of Internal Medicine, researchers analyzed information on vitamin D levels and respiratory infections from nearly 19,000 adults and adolescents who participated in the Third National Health and Nutrition Examination Survey (NHANES III) from October 1988 to October 1994.
The results showed those with the lowest vitamin D levels (less than 10 nanograms per milliliter of blood) were 36% more likely to report having a recent upper respiratory tract infection than those with higher levels (30 ng/mL or higher).
For example, people with asthma with the lowest vitamin D levels were five times more likely to have had a recent respiratory infection. Among those with COPD, recent respiratory infections were twice as common among those with lowest vitamin D levels.
"We are planning clinical trials to test the effectiveness of vitamin D to boost immunity and fight respiratory infection, with a focus on individuals with asthma and COPD, as well as children and older adults -- groups that are at higher risk for more severe illness," Ginde says. "While it's too early to make any definitive recommendations, many Americans also need more vitamin D for its bone and general health benefits."