Vitamin D doesn’t help with asthma, says new review

Vitamin D supplements don’t prevent asthma attacks after all, according to a new review.

A just-published Cochrane review – one of the most comprehensive scientific analyses in the world – has concluded that vitamin D supplements don’t have an effect on asthma attacks in adults or children.

But, the review pointed out, there also wasn’t any harm associated with taking vitamin D supplements.

These findings are different to a previous Cochrane review published by many of the same researchers seven years ago. That review tentatively ruled in favour of vitamin D for asthma.

“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,” says review co-author, Professor Adrian Martineau, a researcher in respiratory infection and immunity at Queen Mary University of London, UK.

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“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.”

This new review analysed 20 randomised controlled trials on vitamin D and asthma, looking at data of 2,225 people with asthma (1,155 children and 1,070 adults).

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The 2016 study, by contrast, included data from nine trials and 1,093 people.

Overall, the new review found no difference between those taking vitamin D supplements and those taking placebos – even among people who were vitamin D deficient when they joined the trial.

“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,” says Martineau.

“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.”

First author Anne Williamson, also at Queen Mary University in London, says they can’t be sure why this new review has found a different result.

“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,” says Williamson.

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

While Cochrane reviews are often considered the final authority on a health-related topic, they can still fall out of date or provide incorrect or different results.

Like all science, the reviews are dynamic and need to be continually updated.

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