According to a new review, taking vitamin D supplements does not reduce the risk of asthma attacks in children or adults.
In a previous Cochrane review, research suggested a reduction in asthma attacks correlated with people taking vitamin D. Contrastingly, the latest findings illuminate that the supplements do not reduce the risk of asthma attacks; however, there is no harm in taking vitamin D.
According to the NHS, asthma attacks kill three people in the UK daily. The most common symptoms of asthma attacks are tightening of the chest, breathlessness, wheezing or a cough. There is no cure for asthma, but treatments such as inhalers and tablets can control symptoms.
Previous research explored a possible link between vitamin D and asthma attacks
More studies have analysed the potential link between vitamin D and asthma attacks and new evidence that contrasts previous findings.
The review was carried out by researchers from the Queen Mary University of London and the University of Edinburgh. Researcher Adrian Martineau, Clinical Professor of Respiratory Infection and Immunity at the Queen Mary University of London, said: “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. 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 the risk of asthma attacks or on control of asthma symptoms compared with a placebo.”
The researchers analysed the results of 20 randomised controlled trials, which included data from 1,155 children and 1,070 adults with asthma. This was compared to nine trials which involved 1,093 people whose data contributed to the previous 2016 review. Most participants had mild to moderate asthma.
Vitamin D has little effect on asthma
They compared patients who took vitamin D with patients who were assigned to take a placebo. The researchers found no statistically significant difference in the number of people who experienced an asthma attack requiring treatment with a course of steroid tablets.
The review did not find any effect of taking vitamin D on asthma control even when people were vitamin D-deficient when they joined the studies, when different doses of the supplement, or in people of different ages.
Professor Martineau said: “In contrast to our previous Cochrane review on this topic, this updated review does not find that vitamin D offers protection against asthma attacks or improves control of asthma symptoms. However, the trials we looked at did not include many people with severe asthma or people with very low levels of vitamin D in their blood, so these are areas where more research is still needed.”
Anne Williamson, the first author of the study who is also from the Queen Mary University of London, commented: “We can’t be certain why this updated review has given a different result to our original study from 2016. 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 increased intake of supplements or fortified foods. Either of these factors could obscure the potential benefits of taking vitamin D supplements. Regardless of the reason, these most recent findings are likely to be correct for people living with asthma today. This also highlights why it’s vital to update reviews when more research is published.”
The most recent Cochrane review included a wider range of clinical trials, compared to the 2016 review. The review team commented that stricter criteria on which studies can be included were applied in the recent review. For example, they excluded studies that did not compare vitamin D with placebo and those that did not monitor patients for at least 12 weeks.
The trials used in the review involved patients taking various types of vitamin D, and further research is necessary to clarify how different forms affect asthma attacks.