A new global collaborative study has confirmed that vitamin D supplementation can help protect against acute respiratory infections. The study, a meta-analysis of twenty-five randomized controlled trials that included a total of more than 11,000 participants, was published online in February in The BMJ.
“Most people understand that vitamin D is critical for bone and muscle health,” says Carlos Camargo, an HMS professor of emergency medicine, a member of the Department of Emergency Medicine at Massachusetts General Hospital, and the study’s senior author. “Our analysis has also found that it helps the body fight acute respiratory infection, which is responsible for millions of deaths globally each year.”
Several observational studies, which track participants over time without assigning a specific treatment, have associated low vitamin D levels with greater susceptibility to acute respiratory infections. A number of clinical trials have been conducted to investigate the protective ability of vitamin D supplementation; some found a protective effect, others did not. Meta-analyses of these trials, which aggregate data from several studies that may have different designs or participant qualifications, also had conflicting results.
To resolve these discrepancies, the research team, led by Adrian Martineau at Queen Mary University of London, conducted an individual-participant data meta-analysis of trials in more than a dozen countries, including Canada, the United Kingdom, and the United States. While traditional meta-analyses compare average data from all participants in each study, individual-participant data meta-analysis separates data from each participant, producing what could be considered a higher-resolution analysis of the data from all studies.
The investigators found that daily or weekly supplementation halves the risk of respiratory infection for individuals with the most severe vitamin D deficiencies. They also found that all participants experienced some beneficial effects from regular vitamin D supplementation. Administering occasional high doses of vitamin D did not produce significant benefits.
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