A large-scale meta-analysis using more than 10,000 participants concludes that vitamin D supplementation may help to prevent acute respiratory tract infections.
Nationwide, acute respiratory tract infections are responsible for 10 percent of ambulance and emergency room visits. There are a number of common risk factors associated with respiratory tract infections from viruses to air pollution and parental smoking. More recently, a number of observational studies have also reported a nutritional risk factor – vitamin d deficiency. However, the results were mixed at best, with some studies supporting the theory, while others were inconclusive.
In an attempt to offer clarification, the largest meta-analysis to date was published in February 2017 in the British Medical Journal. The analysis, carried out by an international group of researchers, is the first to use individual participant data (IPD). In this way, changes measured at different points in time within each participant of each trial can be accounted for, rather than taking a summary (aggregate) of the data. The team used data from 25 randomized controlled trials investigating vitamin D supplementation. In total, data from 11,321 participants were analyzed.
After adjusting for potentially confounding variables, such as sex, age, and study duration, scientists found that vitamin D supplementation produced a 12 percent reduction in the proportion of individuals experiencing at least one acute respiratory tract infection. To put it simply, if 33 people took vitamin D supplements, one acute respiratory tract infection would be prevented. If these results are confirmed, vitamin D supplementation could potentially prevent millions of respiratory infections each year.
Upon further inspection of the data, researchers found that the positive effect was more pronounced in participants who took daily or weekly vitamin D without additional large doses. The effect was also stronger for individuals with more severe vitamin D deficiencies – only 1 in 4 people in this group would need to take vitamin D regularly to prevent one acute respiratory tract infection.
The authors concluded, “Our results add to the body of evidence supporting the introduction of public health measures such as food fortification to improve vitamin D status, particularly in settings where profound vitamin D deficiency is common.” The team also concluded that vitamin D was safe to consume as a supplement and that side effects were very rare.