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Vitamin D supplementation reduces the risk of acute respiratory infections, study suggests

An updated meta-analysis of trials of vitamin D supplementation finds a small reduction in the risk of acute respiratory infection

An international group of trialists, including members of the Asthma UK Centre for Applied Research, show in an updated meta-analysis of supplementation trials, that vitamin D supplementation reduced the risk of acute respiratory infections (ARIs).

Interest in the potential for vitamin D as a treatment to reduce the risk of ARIs has increased since the emergence of the COVID-19 pandemic. Previous studies of vitamin D to prevent ARIs have shown varying results.

The study published in The Lancet Diabetes & Endocrinology updates a previous meta-analysis published in 2017.

The study

The aim of the study was to update the researchers’ previous meta-analysis with more recently published trials examining the effect of vitamin D supplementation on acquisition of ARI. The updated meta-analysis included data from 75,541 participants from 46 studies, with results published between October 2009 and February 2021.

Overall, taking vitamin D reduced the risk of having one or more acute respiratory infections. There was significant heterogeneity in the results of the studies. When the researchers looked at pre-specified subgroups, they found that supplementation was protective: when given daily; for doses of 400-1000 IU; in children aged 1-19 years; and when given for up to a year.

Taken as a whole, whilst the size of these protective effects is small, they remain significant with the addition of further trials to the original meta-analysis. They also throw light on how the frequency, dose and duration of vitamin D supplementation could be key in determining how effective it is against ARIs. Further studies on varying regimens of vitamin D supplementation are needed to investigate this issue.

Future applications

It is currently unknown if these findings are relevant to COVID-19. Additional investigation into vitamin D supplementation for the prevention of COVID-19 is needed.

Professor Chris Griffiths, Centre Director at the Asthma UK Centre for Applied Research, was involved in this study. He said:

This study updates our previous understanding of how vitamin D can be used to prevent acute respiratory infections. Despite the small size of the reduced risk, these data continue to suggest that dosing matters in relation to protection against ARI.

Professor Chris GriffithsCentre Director at the Asthma UK Centre for Applied Research

Read the paper

This publication is available from The Lancet Diabetes & Endocrinology

Cite as

David A Jolliffe, Carlos A Camargo, John D Sluyter, et al. Vitamin D supplementation to prevent acute respiratory infections: a systematic review and meta-analysis of aggregate data from randomised controlled trials, The Lancet Diabetes & Endocrinology, Volume 9, Issue 5, 2021, Pages 276-292, doi: 10.1016/S2213-8587(21)00051-6.

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