Vitamin D deficiency may increase risk of colds, flu

Vitamin D may be an important way to arm the immune system against disorders like the common cold. (File Photo)
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WASHINGTON, Feb. 23 (Chinese media) -- Vitamin D may be an important way to arm the immune system against disorders like the common cold, according to a report published on Monday in the Archives of Internal Medicine.

In the biggest and most nationally representative

study of the association between vitamin D and respiratory infections, conducted

by investigators from the University of Colorado Denver (UC Denver) School of

Medicine, Massachusetts General Hospital (MGH) and Children's Hospital Boston,

people with the lowest blood vitamin D levels reported having significantly more

recent colds or cases of the flu. The risks were even higher for those with

chronic respiratory disorders, such as asthma and emphysema.

"The findings of our study support an important role

for vitamin D in prevention of common respiratory infections, such as colds and

the flu," Adit Ginde, UC Denver Division of Emergency Medicine and lead author

of the study, said. "Individuals with common lung diseases, such as asthma or

emphysema, may be particularly susceptible to respiratory infections from

vitamin D deficiency."

While vitamin C has been used for the prevention of

colds and other respiratory disorders for decades, little scientific evidence

supports its effectiveness. In contrast, in recent years evidence has

accumulated that vitamin D -- most commonly associated with the development and

maintenance of strong bones --may also play a key role in the immune system.

Circumstantial evidence has implicated the wintertime

deficiency of vitamin D, which the body produces in response to sunlight, in the

seasonal increase in colds and flu; and small studies have suggested an

association between low blood levels of vitamin D and a higher risk of

respiratory infections, the report said.

The study analyzed data from the Third National

Health and Nutrition Examination Survey (NHANES III), conducted by the National

Center for Health Statistics. Participants were interviewed in their homes

regarding their health and nutrition, and most participants also received a

physical examination that included collection of blood and other samples for

laboratory analysis. The research team analyzed blood levels of

25-hydroxyvitamin D (25OHD) -- the best measure of vitamin D status -- from

almost 19,000 adult and adolescent NHANES III participants, selected to be

representative of the overall U.S. population.

Study participants with the lowest vitamin D blood

levels -- less than 10 nanogram per milliliter of blood -- were about 40 percent

more likely to report having a recent respiratory infection than were those with

vitamin D levels of 30 or higher. The association was present in all seasons and

even stronger among participants with a history of asthma or chronic obstructive

pulmonary disease (COPD), including emphysema. Asthma patients with the lowest

vitamin D levels were five times more likely to have had a recent respiratory

infection; while among COPD patients, respiratory infections were twice as

common among those with vitamin D deficiency.

"A respiratory infection in someone with otherwise

healthy lungs usually causes a few days of relatively mild symptoms," Carlos

Camargo of the MGH Department of Emergency Medicine and senior author of the

study, said.

"But respiratory infections in individuals with an

underlying lung disease can cause serious attacks of asthma or COPD that may

require urgent office visits, emergency department visits or hospitalizations.

So the impact of preventing infections in these patients could be very large,"

said.

The authors stressed that the study's results need to

be confirmed in clinical trials before vitamin D can be recommended to prevent

colds and flu.

"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 said.

"While it's too early to make any definitive

recommendations, many Americans also need more vitamin D for its bone and

general health benefits. Clinicians and lay people should stay tuned as this

exciting area of research continues to expand," he said.