Researchers in London have identified a mechanism through which vitamin D can significantly reduce the symptoms of asthma and suggest it may offer a new way to treat the debilitating condition, which in the UK alone affects around 5.4 million people and costs the NHS around £1 billion a year.

Catherine Hawrylowicz of King’s College London, and colleagues, write about their discovery in a paper published in the Journal of Allergy and Clinical Immunology this month.

Asthma is a long-term condition where the airways narrow from becoming inflamed and swollen, making it hard to breathe.

Currently patients with severe asthma take steroid tablets, which can have harmful side effects.

But some patients have a type of asthma that is resistant to steroids making it almost impossible to treat, so their asthma attacks are often severe and sometimes even life-threatening, leading to repeated hospital admission.

In their paper, Hawrylowicz and colleagues describe how they found a way that vitamin D may be able to reduce the symptoms of asthma.

It concerns the activity of a natural compound called interleukin-17A (IL-17A) which is part of the immune system. IL-17A protects the body against infection but is also known to worsen asthma symptoms and, in large amounts, to decrease the impact of steroids.

For the study, the team examined three groups of people: 18 patients with steroid-resistant asthma, 10 patients with asthma that responded to treatment with steroids, and 10 healthy people without asthma (the controls).

IL-17A is produced by a group of immune cells called TH17 (T helper 17 cells). The researchers examined these cells in each group of patients and looked at how they produced IL-17A and the amounts.

They found that compared to cells from the healthy controls without asthma, cells from both of the asthma groups had higher levels of IL-17A, with the steroid-resistant group showing the highest levels.

And, they found vitamin D significantly lowered production of IL-17A in cells from all three groups, including the two groups with asthma. Steroids, on the other hand, had little effect on IL-17A production in the cells from patients with asthma.

The team concludes that vitamin D inhibited IL-17A production in all the patients they studied, “irrespective of their clinical responsiveness to steroids”, and these results thus identify “novel steroid-enhancing properties of vitamin D in asthmatic patients“.

The findings therefore suggest vitamin D could be a safe and useful add-on treatment.

If vitamin D proves successful in trials, and is shown to reduce the amount of steroids required, it could have enormous impact on the quality of life of asthma sufferers.

As Hawrylowicz explains in a statement:

“These findings are very exciting as they show that vitamin D could one day be used not only to treat people with steroid resistant asthma but also to reduce the doses of steroids in other asthma patients, reducing the risk of harmful side effects.”

She says the findings were “so positive” that they are already starting a clinical trial in steroid resistant asthma patients to find out more about using vitamin D as a treatment for asthma.

Asthma UK helped fund the study, and the research team is part of the King’s Health Partners Academic Health Sciences Centre.

In another study published recently in the American Journal of Medicine, researchers from Johns Hopkins in the US report that very high blood levels of vitamin D confer no additional benefit, and warn that raising levels of vitamin D in “healthy people” whose levels are normal could do more harm than good.

Written by Catharine Paddock PhD