Vitamin D supplementation to prevent acute respiratory infections: a systematic review and meta-analysis of aggregate data from randomised controlled trials.

A 2017 meta-analysis of data from 25 randomised controlled trials (RCTs) of vitamin D supplementation for the prevention of acute respiratory infections (ARIs) revealed a protective effect of this intervention. We aimed to examine the link between vitamin D supplementation and prevention of ARIs in an updated meta-analysis. For this systematic review and meta-analysis, we searched MEDLINE, Embase, the Cochrane Central Register of Controlled Trials, Web of Science, and the ClinicalTrials.gov registry for studies listed from database inception to May 1, 2020. Double-blind RCTs of vitamin D We identified 1528 articles, of which 46 RCTs (75 541 participants) were eligible. Data for the primary outcome were obtained for 48 488 (98·1%) of 49 419 participants (aged 0-95 years) in 43 studies. A significantly lower proportion of participants in the vitamin D supplementation group had one or more ARIs (14 332 [61·3%] of 23 364 participants) than in the placebo group (14 217 [62·3%] of 22 802 participants), with an OR of 0·92 (95% CI 0·86-0·99; 37 studies; I Despite evidence of significant heterogeneity across trials, vitamin D supplementation was safe and overall reduced the risk of ARI compared with placebo, although the risk reduction was small. Protection was associated with administration of daily doses of 400-1000 IU for up to 12 months, and age at enrolment of 1·00-15·99 years. The relevance of these findings to COVID-19 is not known and requires further investigation. None.

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Declaration of interests ARM reports grants from the Fischer Family Trust, Pharma Nord, DSM Nutritional Products, the AIM Foundation, Cytoplan, and Thornton & Ross. CG reports grants from the Health Technology Assessment Programme of the UK National Institute of Health Research. WJ reports grants from Chiesi and Astra Zeneca. REN reports grants from the Australian National Health and Medical Research Council. ECG became an employee of GSK Canada in November 2013, after the completion and publication of her vitamin D RCT. AMH reports grants from NHLBI and the Office of Dietary Supplements. JRR reports grants from Dartmouth College, non-financial support (provision of study pills for trial) from Pfizer Consumer Healthcare and has a patent for calcium chemoprevention of adenoma (issued to John Baron & Dartmouth College). HAB-F reports grants from DSM Nutritional Products, travel expenses from Pfizer, and speaker honoraria from Wild Pharma, Mylan, and Roche Diagnostics. All other authors declare no competing interests. DAJ and ARM are the manuscript's guarantors and they affirm that this is an honest, accurate, and transparent account of the study being reported, and that no important aspects of the study have been omitted.