By Margarita Nahapetyan
Vitamin D appears to be important for the immune system to fight against the common cold, according to the experts from the University of Colorado Denver (UC Denver) School of Medicine, Massachusetts General Hospital (MGH) and Children's Hospital Boston.
The largest to date study suggests that people develop cold and flu not only because of a damp weather, but also because of a lack of the sunshine. Rates of sickness were even higher among people who already had chronic respiratory problems, 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," said Adit Ginde, MD, MPH, at UC Denver Division of Emergency Medicine and a lead researcher of the study. "Individuals with common lung diseases, such as asthma or emphysema, may be particularly susceptible to respiratory infections from vitamin D deficiency."
Researchers said that although vitamin C has been used for the prevention of common colds and other respiratory infections for many years, there is little scientific evidence to support its effectiveness. In contrast, few recent studies have found that vitamin D, mostly associated for its role in the development and maintenance of strong bones, may also play a critical role in the function of the immune system.
Dr. Ginde and his colleagues analyzed vitamin D levels of nearly 19,000 adults and adolescents who took part in the National Health and Nutrition Examination Survey (NHANES), and were selected to represent the overall U.S. population. Blood samples were taken to measure levels of 25-hydroxyvitamin D, considered to be the optimal measure of vitamin D status. In addition, all the participants underwent physical examinations and were asked a question if they had cough, cold, or other acute illness in the past several days.
Although no minimum vitamin D level the best for health has been established, there is a general consensus that people ought to have at least 30 nanograms per milliliter of blood - sometimes described as about 80 nanomoles per liter. At least 50 per cent of people in the new study had that minimum. Therefore, the researchers divided the NHANES participants into 3 groups: those with 30ng/ml or more, those with a big vitamin deficiency - 10ng/ml or less, and those in the middle.
The results showed that those participants who were in the group with the lowest levels of vitamin D, were 36 per cent more likely to report having a recent upper respiratory tract infection than those with higher levels of the vitamin. Risks of infection s for people in the middle group fell between those rates. The finding was consistent across all races and ages.
The association was present in all seasons and was even stronger among participants with a history of asthma or chronic obstructive pulmonary disease (COPD), including emphysema. Among people with asthma, those who had vitamin D deficiency were 5 times more likely to catch a cold than people with healthy levels. And the risk of respiratory infection was doubled among vitamin D-deficient patients with chronic obstructive pulmonary disease compared with those patients who had normal levels of the vitamin.
The experts concluded that the findings of the research yet need to be expanded and confirmed in clinical trials before vitamin D could be recommended to fight colds and the 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," Dr Ginde said. "While it is too early to make any definitive recommendations, many Americans also need more vitamin D for its bone and general health benefits. Clinicians and laypeople should stay tuned as this exciting area of research continues to expand."
According to American Dietetic Association (ADA), vitamin D can be found foods such as canned tuna, cereals and fortified milk or juice. The body can also be triggered to naturally produce vitamin D (also known as sunshine vitamin) after an adequate exposure to sunlight.