Vitamin D supplements may have a role to play in warding off severe asthma attacks, the results of a new study suggest.

Asthma affects over 300 million people worldwide, including around 470,000 people in Ireland. It is estimated to cause almost 400,000 deaths globally every year.

Asthma deaths usually occur during ‘attacks' or exacerbations, when the affected person suffers a worsening of symptoms. These can often be triggered by viral upper respiratory infections.

Vitamin D is thought to protect against such attacks by boosting the immune system's response to respiratory viruses and reducing harmful airway inflammation.

UK researchers decided to look into this further. They analysed the data relating to almost 1,000 people who had taken part in seven trials involving the use of vitamin D supplements.

They found that taking supplements in addition to standard asthma medication led to a 30% reduction in the rate of asthma attacks that required treatment with steroid tablets or injections.

It also led to a 50% reduction in the risk of experiencing at least one asthma attack that required a visit to an Emergency Department and/or hospitalisation.

"These results add to the ever growing body of evidence that vitamin D can support immune function as well as bone health. People die from asthma attacks every day. Vitamin D is safe to take and relatively inexpensive so supplementation represents a potentially cost-effective strategy to reduce this problem," commented lead researcher, Prof Adrian Martineau, of Queen Mary University of London.

The study noted that vitamin D appeared to have a particularly protective effect in people who had low vitamin D levels to begin with. They recorded a 55% reduction in the rate of asthma attacks that required treatment with steroid tablets or injections.

The researchers acknowledged that most of the participants were adults with mild to moderate asthma, so the findings may not apply to children and adults with severe asthma.

"Further clinical trials are ongoing internationally, and we hope to include data from them in a future analysis to determine whether the promise of today's results is confirmed in an even larger and more diverse group of patients," they added.

Details of these findings are published in the medical journal, The Lancet Respiratory Medicine.