Overall the review found evidence that taking a vitamin D supplement could reduce the risk of severe asthma attacks requiring hospital admission from 6% to around 3%.
They also found the rate of asthma attacks needing steroid treatment dropped from 0.44 to 0.28 attacks per person per year after vitamin D supplementation – but that the so-called sunshine vitamin did not improve lung function or everyday asthma symptoms.
“Meta-analysis of a modest number of trials in people with predominantly mild to moderate asthma suggests that vitamin D is likely to reduce both the risk of severe asthma exacerbation and healthcare use,” concluded the researchers from the UK, Japan and Australia.
‘This is the first hard evidence’
There has been growing interest in the potential role of vitamin D in asthma management with past research linking low blood levels of the vitamin to an increased risk of asthma attacks in children and adults.
A review in 2015 concluded that vitamin D supplementation could reduce the risk of asthma exacerbation by 74% in children.
The Cochrane review looked at seven trials on the subject involving 435 children and two studies involving 658 adults.
Lead author and professor at the Asthma UK Centre for Applied Research at Queen Mary University of London, Adrian Martineau, said: “Several other micronutrients have been proposed to have potential benefit for asthma prevention and control, but to our knowledge this is the first hard evidence showing that a micronutrient can reduce risk of asthma attacks.”
However the team urged caution with the findings, saying several questions remained unanswered.
“This is an exciting finding – but it is unlikely that vitamin D will benefit all asthma sufferers,” Professor Martineau told us.
The review showed a benefit for prevention of asthma attacks, but not for improvement in day-to-day symptoms of asthma.
“About 50% of asthma sufferers don’t get severe attacks, so our study does not suggest a benefit of vitamin D for this group,” he said.
It was also still unclear whether vitamin D would benefit all asthma sufferers or just those who have low vitamin D levels to begin with.
Second review to come
Yet the team were now working on individual patient data (IPD) meta-analysis to pool all the raw data from each trial in a single database.
They hoped this dataset would allow them to run sub-group analyses and find if some patients benefit more from vitamin D than others depending on their baseline vitamin D levels.
The results of this second meta-analysis are expected by the end of the year.
Source: Cochrane Database of Systematic Reviews
“Vitamin D for the management of asthma”
Authors: A. R. Martineau, C. J. Cates, M. Urashima, M. Jensen, A. P. Griffiths, U. Nurmatov, A. Sheikh, C. J. Griffiths