# 4648
For years there has been speculation that the seasonality of influenza could be at least partially explained by lower levels of Vitamin D experienced by most people during the winter.
While cooler temperatures and lower humidity levels have been linked to flu transmission, along with increased indoor contacts during the winter, anecdotal evidence has often linked Vitamin D deficiency as well.
Last summer we learned that the Public Health Agency in Canada was looking at the protective qualities of Vitamin D in Scientists To Study Vitamin D And The Flu, and in February of 2009 we saw a study (see Vitamin D To Ward Off Flu?) that found an inverse relationship between a person's level of serum 25-hydroxyvitamin D and a recent bout with a cold or flu.
Those who had recently experienced an ILI or other respiratory illness, were more likely to have lower than normal Vitamin D levels.
The median serum level of 25-hydroxyvitamin D, among more than 18,000 people tested, was 29 ng/ml.
Those with a serum level below 10 ng/ml (considered very low), were 40% more likely to have had a recent respiratory illness than those with a serum level above 30 ng/ml.
The link between Vitamin D levels and the risk for respiratory infections was stronger in those with asthma or COPD.
Today (well, yesterday actually . . . ) PLoS One published a study that strongly suggests that raising the blood serum level of Vitamin D to over 38 ng/ml could result in a significant reduction in viral respiratory illnesses.
I’ve reproduced the abstract below, but follow the link to read the report in its entirety.
James R. Sabetta, Paolo DePetrillo, Ralph J. Cipriani, Joanne Smardin, Lillian A. Burns, Marie L. Landry Research Article, published 14 Jun 2010 doi:10.1371/journal.pone.0011088
Background
Declining serum concentrations of 25-hydroxyvitamin D seen in the fall and winter as distance increases from the equator may be a factor in the seasonal increased prevalence of influenza and other viral infections. This study was done to determine if serum 25-hydroxyvitamin D concentrations correlated with the incidence of acute viral respiratory tract infections.
Methodology/Findings
In this prospective cohort study serial monthly concentrations of 25-hydroxyvitamin D were measured over the fall and winter 2009–2010 in 198 healthy adults, blinded to the nature of the substance being measured. The participants were evaluated for the development of any acute respiratory tract infections by investigators blinded to the 25-hydroxyvitamin D concentrations.
The incidence of infection in participants with different concentrations of vitamin D was determined. One hundred ninety-five (98.5%) of the enrolled participants completed the study. Light skin pigmentation, lean body mass, and supplementation with vitamin D were found to correlate with higher concentrations of 25-hydroxyvitamin D.
Concentrations of 38 ng/ml or more were associated with a significant (p<0.0001) two-fold reduction in the risk of developing acute respiratory tract infections and with a marked reduction in the percentages of days ill.
Conclusions/Significance
Maintenance of a 25-hydroxyvitamin D serum concentration of 38 ng/ml or higher should significantly reduce the incidence of acute viral respiratory tract infections and the burden of illness caused thereby, at least during the fall and winter in temperate zones.
The findings of the present study provide direction for and call for future interventional studies examining the efficacy of vitamin D supplementation in reducing the incidence and severity of specific viral infections, including influenza, in the general population and in subpopulations with lower 25-hydroxyvitamin D concentrations, such as pregnant women, dark skinned individuals, and the obese.
