Administering doses of a vitamin D supplement to patients can significantly mitigate their risk of developing acute respiratory tract infections, according to a recent study published by the BMJ.

“[Existing] epidemiological and in vitro data have prompted numerous randomized controlled trials to determine whether vitamin D supplementation can decrease the risk of acute respiratory tract infection,” wrote the authors of the study, led by Adrian R. Martineau, PhD , of Queen Mary University of London. “A total of five aggregate data meta-analyses incorporating data from up to 15 primary trials have been conducted to date [but] all but one of these aggregate data meta-analyses reported statistically significant heterogeneity of effect between primary trials.”

Dr. Martineau and his colleagues conducted a search of the Medline, Embase, and Web of Science databases, the Cochrane Central Register of Controlled Trials,, and the International Standard Randomized Controlled Trials Number registry to find trials that were randomized, double-blind, and placebo-controlled involving patients receiving Vitamin D supplementation, either with D2 or D3.

A total of 532 studies were reviewed by a panel, of which 25 studies were ultimately selected for inclusion in this analysis. The studies included were of varying lengths in terms of trial periods and involved a total of 11,321 subjects ranging from 0 to 95 years of age. Of these, 10,933 (96.6%) subjects experienced at least one acute respiratory tract infection.

No significant benefit was found in subjects who had already experienced an infection, yielding an odds ratio of 0.98 (95% CI, 0.80-1.20; P = .83). Analysis performed to quantify the risk of infection with or without Vitamin D showed that taking Vitamin D supplements significantly decreased infection risk, with an OR of 0.88 (95% CI, 0.81-0.96; P less than .001) after adjusting for age, sex, and the duration of the trial.

Results also demonstrated that bolus doses of Vitamin D did not offer any beneficial value to subjects. Those who received daily or weekly doses without bolus had a better OR, compared with those who did receive at least one bolus dose: 0.81 (95% CI, 0.72-0.91) versus 0.97 (95% CI, 0.86-1.10), respectively (P = .05). Individuals whose baseline 25-hydroxyvitamin D levels were lower than 25 nanomols per liter experienced a greater benefit than those whose levels were above 25: OR = 0.30 (95% CI, 0.17-0.53) and OR = 0.75 (95% CI, 0.60-0.95), respectively (P = .006).

“Our study reports a major new indication for vitamin D supplementation: the prevention of acute respiratory tract infection,” Dr. Martineau and his coauthors concluded, adding that a potential application for these findings would be “the introduction of public health measures such as food fortification to improve vitamin D status, particularly in settings where profound vitamin D deficiency is common.”

The study was funded by a grant from the National Institute of Health Research. Dr. Martineau and his coauthors did not report any relevant financial disclosures.


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