Vitamin D Does Not Reduce Risk of Asthma Attacks, Study Finds

In contrast to a previous review, taking vitamin D supplements does not reduce risk of asthma attacks, according to new research.

Researchers found no significant difference in the number of people who experienced asthma attacks when comparing patients who were taking vitamin D supplements with patients taking a placebo.

“Vitamin D deficiency has been linked to an increased risk of severe asthma attacks, and our previous Cochrane review, published in 2016, found that vitamin D reduced the risk of asthma attacks,” said Adrian Martineau, B Med Sci, DTM&H, MRCP, PhD, FRSB, clinical professor of respiratory infection and immunity at Queen Mary University of London, in a statement.1 “However, more studies have been published since then, and when we included the extra data in our updated review, the overall results changed. We found that vitamin D supplements had no effect on risk of asthma attacks or on control of asthma symptoms compared with a placebo.”

The results of this newest review were published in Cochrane Database of Systematic Reviews.2

Since the previous review, debates have surrounded the effectiveness and safety of taking vitamin D supplements to reduce the risk of asthma attacks, which this review aimed to confirm.

This review included 20 studies that covered 1155 children and 1070 adults with asthma. Trials were between 3 and 40 months. All except 2 trials administered cholecalciferol, a form of vitamin D3. Like the authors' previous review, most of the patients had mild to moderate asthma and were vitamin D deficient (25-hydroxyvitamin D [25(OH)D] < 25 nmol/L) at baseline.

As a result, administering vitamin D or its hydroxylated metabolites neither reduced nor increased the proportion of individuals who experienced 1 or more asthma exacerbations when treated with systemic corticosteroids (odds ratio [OR], 1.04; 95% CI, 0.81-1.34), with an absolute risk of 226 per 1000 (95% CI, 185-273) population in the pooled vitamin D group compared with the baseline risk of 219 per 1000 in the pooled placebo group. Additionally, the researchers found no effect on the incidence of serious adverse events (OR, 0.89; 95% CI, 0.56-1.41).

“We can’t be certain why this updated review has given a different result to our original study from 2016,” said Anne Williamson, MBBS '25, first study author, also from Queen Mary University of London, in a statement. “It could be that people with asthma may be getting better treatment than previously. Or it could be that, in general, rates of vitamin D deficiency have decreased over time, due to increasing intake of supplements or fortified foods.”

The researchers noted that although most of the trials administered cholecalciferol, a trial that used calcidiol, a compound the body can make from vitamin D, reported an improvement in asthma symptoms in patients. The researchers confirmed that more research needs to be done to determine if there exist any benefits in taking vitamin D to reduce risk of asthma attacks.


1. Cochrane review finds that vitamin D does not reduce risk of asthma attacks. News release. EurekAlert; February 5, 2023. Accessed February 14, 2023.

2. Williamson A, Martineau AR, Sheikh A, Jolliffe D, Griffiths CJ. Vitamin D for the management of asthma. Cochrane Database Syst Rev. February 2023. doi:10.1002/14651858.CD011511.pub3

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