Vitamin D May Cut Risk of Flu
Study Shows Vitamin D May Help Prevent Respiratory Tract Infections
WebMD News Archive
June 16, 2010 -- Vitamin D may reduce the incidence and severity of influenza and other infections of the upper respiratory tract, new research indicates.
Simple steps such as eating foods rich with vitamin D and getting more sunshine may help to reduce your chances of contracting flu and other similar illnesses, shows a study by scientists at Yale University School of Medicine and Greenwich Hospital in Connecticut.
"People in the South and West get more sun than in the North, which is good for them, because you get vitamin D from the sun," study researcher James R. Sabetta, MD, of the Yale University School of Medicine and Greenwich Hospital, Conn., tells WebMD. "It's not a panacea, but it helps."
Sabetta and his team of colleagues followed 198 healthy adults during the fall and winter of 2009-2010 to see if declining levels of vitamin D in the fall and winter could be a factor in the seasonal increased prevalence of respiratory viral infections, such as flu.
The study shows people who maintain vitamin D blood levels of 38 nanograms per milliliter or more are less likely to get viral infections such as flu than people with less in their blood.
Of 18 people who maintained that level during the study period, only three developed viral infections.
But of the 180 other participants with less vitamin D in their blood, 81(45%), did get sick with viral infections.
And those with higher levels of vitamin D also experienced a marked reduction in the number of days they were ill, Sabetta tells WebMD.
In addition to getting more sun and consuming milk and foods with vitamin D, he recommends supplements, especially for people in areas with less sunlight and for those who spend daylight hours in darker, indoor environments.
"If you have a level of 38, your risk is down 50%," he tells WebMD. "A lot of people don't have an adequate level, and 38 is a little above what you should have to be considered in the sufficient range. There are a billion people worldwide with levels below 30."
And 30 is considered "sufficient," he says.
Watching for Signs of Illness
Participants in the study had blood samples drawn monthly using a sophisticated technique to accurately measure vitamin D levels. They didn't know that vitamin D was being measured, and even investigators didn't know until the end of the study.
All participants were asked to report signs of illness, such as nasal congestion, sore throat, cough with or without fever, chills, fatigue and general malaise.
Those reporting any symptoms were seen the same day at the study site by one of the infectious disease investigators.
People in the study kept a diary of symptoms and were called every one to three days during the illness to review any signs of symptoms until they were better. The investigators recorded the duration of each symptom, the total duration of the illness, and any antimicrobials administered.