Vitamin D may help in reducing the occurrence and severity of influenza and viral respiratory tract infections, a new study has found.
The study conducted by investigators at Greenwich Hospital and Yale University School of Medicine, was led by James R. Sabetta, M.D., and it followed 198 healthy adults during the fall and winter of 2009-2010.
The basis for the study was to determine if the declining concentrations of vitamin D seen in the fall and winter in a temperate climate could be a factor in the seasonal increased prevalence of respiratory viral infections such as the flu.
In the double-blinded study, participants had blood samples drawn monthly using a 25-hydroxyvitamin D test to accurately measure vitamin D levels.
Participants did not know that vitamin D was being measured, and the investigators did not know the levels until the end of the study.
All participants were asked to report any evidence of an acute respiratory tract infection (nasal congestion, sore throat, and/or cough with or without fever, chills, fatigue and general malaise).
Of the 18 participants who maintained vitamin D levels of 38 ng/ml or higher during the study period, only three (16.6 percent) developed viral infections.
Of the 180 other participants, 81 (45 percent) developed viral infections. Those with the higher vitamin D levels also experienced a marked reduction in the number of days ill.
According to the release, the data in this study suggests that supplementing with vitamin D to achieve a blood level 38 ng/ml or higher could result in a significant health benefit by reducing the incidence of viral infections of the respiratory tract.
Further studies are necessary to examine the efficacy of vitamin D supplementation in the prevention of specific infections, including influenza, the release added.
Vitamin D, which we get to some extent from exposure to natural sunlight, has known effects on the immune system.
The association between vitamin D deficiency and susceptibility to infections of the respiratory tract has been suggested for many years, and Dr. Sabetta's study helps to solidify this association, the release said.
Importantly, the study demonstrated a beneficial effect of a concentration of vitamin D only slightly higher than the lower limit of 30 ng/ml currently considered to represent a sufficient level, it added.
The study has been published in the peer-reviewed open access journal PloS ONE.