Vitamin D supplements along with standard medication may halve the risk of suffering a severe asthma attack requiring hospital attendance, a study claims.
Asthma deaths arise primarily during episodes of acute worsening of symptoms, known as attacks or 'exacerbations', which are commonly triggered by viral upper respiratory infections, researchers said.
Vitamin D is thought to protect against such attacks by boosting immune responses to respiratory viruses and dampening down harmful airway inflammation, they said.
Researchers from Queen Mary University of London (QMUL) in the UK analysed data from 955 participants in seven randomised controlled trials, which tested the use of vitamin D supplements.
The study, published in The Lancet Respiratory Medicine journal, found that vitamin D supplementation resulted in a 30 per cent reduction in the rate of asthma attacks requiring treatment with steroid tablets or injections.
Researchers also found that the supplementation resulted in a 50 per cent reduction in the risk of experiencing at least one asthma attack requiring hospitalisation - from six per cent of people experiencing such an event to three per cent.
Vitamin D supplementation was found to be safe at the doses administered.
No instances of excessively high calcium levels or renal stones were seen, and serious adverse events were evenly distributed between participants taking vitamin D and those on placebo, researchers said.
"These results add to the ever growing body of evidence that vitamin D can support immune function as well as bone health," said lead researcher, Adrian Martineau, professor at QMUL.
"Vitamin D is safe to take and relatively inexpensive so supplementation represents a potentially cost-effective strategy to reduce this problem," Martineau added
