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20-06-2010 | Infectious disease | Article

Vitamin D may protect against influenza


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MedWire News: Results from a US study suggest that individuals can reduce their risk for viral respiratory tract infections, including influenza, by boosting their levels of vitamin D.

Writing in the journal PLoS ONE, James Sabetta (Yale University School of Medicine, New Haven, Connecticut) and colleagues explain that vitamin D, which is mainly produced in the body on exposure to the sun, has known effects on the immune system and helps suppress inflammation.

They add: “Declining serum concentrations of 25-hydroxyvitamin D (25[OH]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.”

To investigate, the team studied 198 healthy adults (113 women), aged 20–88 years, during the fall and winter of 2009–2010. Blood samples from the participants were collected each month and assessed for 25(OH) D levels, and the occurrence and timing of acute respiratory tract infections were recorded.

Of the 195 participants who completed the study, 84 suffered 103 acute viral infections during the 4-month study period.

Partition analysis revealed that a 25(OH)D concentration of 38 ng/ml best discriminated between groups that did or did not develop viral infections of the respiratory tract.

The researchers found that 83.3% of the 18 participants who maintained a 25(OH) D concentration of 38 ng/ml or higher did not experience any respiratory tract infections during the study, whereas only 55% of the 180 participants whose concentrations were below 38 ng/ml during the study period survived without infection.

Indeed, participants with a 25(OH)D concentration of 38 ng/ml or higher during the entire study period were 2.7 times less likely to experience a viral infection of the respiratory tract than those with a vitamin D level below this threshold.

The researchers also note that light skin pigmentation, lean body mass, and supplementation with vitamin D all correlated with higher serum concentrations of 25(OH)D.

Sabetta and team conclude: “The data in this study suggest 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.”

They add: “Our findings may 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 specific subpopulations, such as pregnant women, dark skinned individuals, and the obese.”

MedWire ( is an independent clinical news service provided by Current Medicine Group, a trading division of Springer Healthcare Limited. © Springer Healthcare Ltd; 2010

By Mark Cowen

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