Last year I wrote a number of posts relating to mechanisms related to mucosal immune defences, in particular the innate immune defences and how we as Nutritional Therapists may advise our patients of evidence based strategies. This paper out in the open access journal Plos One adds further validity to the vitamin D recommendations I proposed.
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 paper in PLOS Biology describes how almost 200 adults had their serum 25-hydroxyvitamin D levels measured, without knowing what was been investigated.
One hundred ninety-eight participants, 85 men and 113 women, with an age range of 20–88, were enrolled in the study.
The researcher found that people with fair skin, lean body mass and who supplemented with vitamin D had the highest levels of 25-hydroxyvitamin D. People who achieved 38ng/ml or higher 25-hydroxyvitamin D level had a remarkable 50% reduction in the risk of developing acute respiratory tract infections and a significant reduction in the number of days ill (p<0.0001).
For participants with 25-hydroxyvitamin D concentrations ≥38 ng/ml, the median duration of illness was 6 days (3 infections, range 2–8 days); for participants with concentrations <38 ng/ml, the median duration was also 6 days (100 infections, range 2–27 days). For influenza, the median durations for the high and low 25-hydroxyvitamin D groups were 2 days (1 infection with no antivirals given) and 9 days (6 infections, range 2–20 days, with antivirals in two participants), respectively. The number of infections in the participants with concentrations ≥38 ng/ml was too small to determine if these differences in illness duration were statistically significant.
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.
It is estimated that 1 billion people worldwide have vitamin D concentrations under 30 ng/ml, and a much larger number would be expected to have concentrations under 38 ng/ml, as found in 81.3% of the participants for entire duration of this study. The average adult has 2–3 viral respiratory tract infections each year, resulting in countless physician visits, days lost from school and work, and enormous direct and indirect costs.
The data in this study suggests that supplementing with vitamin D to raise the concentrations in the general population to above 38 ng/ml could result in a significant health benefit by reducing the burden of illness from viral infections, at a minimum from viral infections of the respiratory tract in healthy adults living in temperate climates.
 Sabetta JR, DePetrillo P, Cipriani RJ, Smardin J, Burns LA, Landry ML. Serum 25-hydroxyvitamin d and the incidence of acute viral respiratory tract infections in healthy adults. PLoS One. 2010 Jun 14;5(6):e11088