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Vitamin D for protection against acute respiratory tract infection.

Martineau AR, Joliffe DA, Hooper RL, Greenberg L, Aloia JF et al. 2016. Vitamin D supplementation to prevent acute respirator tract infections: systematic review and meta-analysis of individual participant data. BMJ; 356:i6583 doi: 10.1136/bmj.i6583

Acute respiratory tract infections (ARTIs) are a major cause of global morbidity and mortality. Whilst observational studies have consistently reported associations between low serum concentration of 25-hydroxyvitamin D (25(OH)D) and susceptibility to ARTIs, results of randomised controlled trials to determine whether vitamin D supplementation can decrease the risk of ARTIs have been conflicting. In the current study, authors conducted a systematic review and meta-analysis of individual participant data (IPD) from previous randomised controlled trials to assess for an overall effect of vitamin D supplementation and risk of ARTI, and to identify factors modifying this effect.

Studies eligible for inclusion in the review were randomised, double-blind, placebo controlled trials of supplementation with vitamin [D.sub.3] or vitamin [D.sub.2] of any duration, that had been approved by a research ethics committee and had ARTI incidence data that was collected prospectively and prespecified as an efficacy outcome. Studies reporting results of long-term follow-up of primary randomised controlled trials were excluded. IPD were requested from the principal investigator for each eligible trial with data extracted for baseline demographics, including age, sex, racial or ethnic origin, influenza vaccination status, history of asthma or COPD, and serum 25(OH)D concentration. Follow up data extracted included number of ARTI (upper and/or lower), time to first ARTI, concomitant antibiotic usage, days of work/school missed, and serum 25(OH)D concentration at final follow-up. The primary outcome for the study was incidence of ARTI, incorporating upper, lower, or unclassified location.

Of 532 studies identified and assessed for eligibility, 25 studies with a total population of 11,321 randomised participants fulfilled the study criteria. Of these, outcome data for primary analysis was available for 10,933 participants. Vitamin D supplementation resulted in a statistically significant reduction in the proportion of participants experiencing at least one ARTI. Subgroup analysis revealed that daily or weekly vitamin D supplementation without additional bolus doses protected against ARTI, but regimens with large bolus doses did not. The protective effect was greatest in participants with profound vitamin D deficiency at baseline; however, those with higher baseline 25(OH)D concentrations also experienced benefit. Vitamin D supplementation was found to be safe and well tolerated, and did not influence the proportion of participants experiencing adverse events.

The study and its results are strengthened by its size with large participant numbers, with only a small proportion of randomised participants having missing outcome data. The study may have been insufficiently powered to detect effects in some subgroups and for secondary outcomes. Overall, the authors concluded vitamin D to be effective in the prevention of ARTI, and that people who are very deficient in vitamin D and those receiving daily or weekly supplementation without additional bolus experienced most benefit. These findings provide good evidence to support clinical practice of vitamin D supplementation for prevention of acute respiratory tract infection.
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Title Annotation:Reviews of medical journal articles
Author:Tester, Jodie
Publication:Australian Journal of Herbal Medicine
Article Type:Report
Date:Jun 1, 2017
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