A fresh review of the evidence has led Cochrane to change its mind on the use of Vitamin D supplements to reduce the risk of asthma attacks.

In 2016, Cochrane reviewers concluded that there was a reduced risk of asthma attack in people taking vitamin D supplementation, based on nine trials involving 1,093 people. However, the latest look at the evidence, which included 20 randomised clinical trials and data on 1,155 children and 1,070 adults with asthma, found no statistically significant difference in the number of exacerbations experienced by those taking vitamin D or those taking a placebo.

Based on what was deemed high-quality evidence, the analysis showed an odds ratio (OR) of 1.04, which equated to an absolute risk of 226 per 1,000 in the vitamin D group, compared to a baseline risk of 219 participants per 1,000 in the control arm.

Similarly, there was no impact of vitamin D supplementation on the rate of exacerbations needing systemic corticosteroids (rate ratio 0.86) or the time to first exacerbation (hazard ratio 0.82), according to the paper.

Vitamin D supplements also had no impact on asthma control in people who were vitamin D deficient at baseline, while Vitamin D dose, frequency of dosing regimen, or age also had no such effect, researchers from Queen Mary University of London and the University of Edinburgh said.

However, they did emphasise that people with severe asthma or very low Vitamin D levels were poorly represented in the review, and so warrant further exploration.

The researchers were uncertain as to why the updated review had a different outcome than that undertaken in 2016, but suggested that reasons might include better treatment of asthma or a general decline in vitamin D deficiency over time.

“Either of these factors could obscure potential benefits from taking vitamin D supplements,” said first study author Anne Williamson, a medical student at Queen Mary University of London, and last year’s winner of the BTS Medical Student Abstract Prize (see our story here).

“Regardless of the reason, these most recent findings are likely to be correct for people living with asthma today,” she added.