Vitamin D supplements protect against cold and flu, study finds

By Sally Robertson, B.Sc.Feb 16 2017

The use of Vitamin D supplements can help to protect against acute respiratory infections, according to a new study.

If everybody took the supplements, more than three million people could ward off colds and flu every year, say the authors of the world-wide, collaborative study.

Vitamin D supplementation has been a hot topic in the medical community recently, with experts divided over whether it is beneficial or not. A number of observational studies have found an association between low vitamin D levels and increased susceptibility to acute respiratory infections and several clinical trials have found a protective effect of vitamin D supplementation. However, other trials have shown no protective effect and meta-analyses of all the trials have shown contradictory results.

To settle the issue, Adrian Martineau (Queen Mary University of London, UK) and colleagues carried out an individual participant data meta-analysis of 25 trials conducted across 14 countries and including almost 11,000 individuals (aged up to 95 years). While conventional meta-analyses compare data averaged out across all participants in each study, individual participant analysis looks at data for each person, thereby generating what could be regarded higher quality data across all of the studies.

As reported in The BMJ, the researchers found that vitamin D supplementation on a daily or weekly basis was of some benefit to all participants. The benefit was the greatest for individuals with the most significant vitamin D deficiency, with their risk of respiratory infection being cut in half.

Most people understand that vitamin D is critical for bone and muscle health. Our analysis has also found that it helps the body fight acute respiratory infection, which is responsible for millions of deaths globally each year."

Senior author Carlos Camargo, Massachusetts General Hospital.

Respiratory tract infection refers to any infection of the throat, airways, sinuses or lungs, with the common cold being the most widespread of the illnesses. At least one acute respiratory tract infection affects at least 70% of the population every year. In the UK, about 25% of individuals seek treatment every year and the infections result in 300,000 hospital admissions and 35,000 deaths annually.

“Assuming a UK population of 65 million, and that 70% have at least one acute respiratory infection each year, then daily or weekly vitamin D supplements will mean 3.25 million fewer people would get at least one acute respiratory infection a year,” says Martineau.

Experts have said the study has implications for public health policy and may lead to foods being fortified with vitamin D to address the high levels of vitamin D deficiency in the UK.