Could vitamin D supplements protect against acute respiratory infections?

A new meta-analysis study has confirmed that regular vitamin D supplementation could help protect against acute respiratory infections, especially in individuals with low baseline vitamin D levels.

It had previously been reported in several observational studies that low levels of vitamin D were associated with increased susceptibility to respiratory infections. However, clinical trials to test this hypothesis have produced conflicting results, as have prior meta-analyses.

The study, led by researchers from Queen Mary’s University of London (UK) and published in the British Medical Journal, analyzed 25 randomized, controlled trials including almost 11,000 participants. The team utilized a statistical analysis that separates out individual patient data, producing a higher-resolution result than previous meta-analyses, which took average data from all trial participants.

Lead researcher Adrian Martineau from Queen Mary’s University commented: “This major collaborative research effort has yielded the first definitive evidence that vitamin D really does protect against respiratory infections. Our analysis of pooled raw data from each of the 10,933 trial participants allowed us to address the thorny question of why vitamin D ‘worked’ in some trials, but not in others.”

The researchers discovered that daily or weekly supplementation had the greatest benefit for individuals with lower baseline vitamin D levels, reducing the risk of respiratory infection by half. The team observed that regular supplements also had beneficial effects on patients with higher baseline vitamin D levels, although these were more modest at a 10% reduction in the risk of acute respiratory infection.

“Most people understand that vitamin D is critical for bone and muscle health,” stated author Carlos Camargo (Massachusetts General Hospital; MA, USA). “Our analysis has also found that it helps the body fight acute respiratory infection, which is responsible for millions of deaths globally each year.”

Vitamin D is thought to induce protection against respiratory viruses by boosting the level of antimicrobial peptides in the lungs.  Acute respiratory infections are responsible for high levels of morbidity and mortality across the globe and introducing vitamin D supplements could be a highly cost-effective method to reduce this burden.

Camargo explained: “Acute respiratory infections are responsible for millions of emergency department visits in the United States. These results could have a major impact on our health system and also support efforts to fortify foods with vitamin D, especially in populations with high levels of vitamin D deficiency.”

Catherine Hawrylowicz, from Kings College London (UK) and spokesperson for the British Society for Immunology reacted to the study: “These findings are likely to be particularly important in individuals for whom acute respiratory tract infections are life-threatening, such as those with asthma and chronic obstructive pulmonary disorder, who are frequently profoundly vitamin D deficient. Since the authors conclude that vitamin D is safe, further targeted studies in such ‘at risk’ populations seem highly desirable.”

Sources: Martineau AR, Jolliffe DA, Greenberg L et al. Vitamin D supplementation to prevent acute respiratory tract infections: systematic review and meta-analysis of individual participant data. BMJ. 356, i6583 (2017);,


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