Asthma affects around 5.4 million people in the UK.
Severe asthma is usually treated with steroid tablets. However, some people are resistant to steroid treatment for their asthma, and others find steroids bring harmful side effects.
When a person's asthma is difficult to treat, they are more likely to be admitted hospital with severe or life-threatening asthma attacks.
IL -17A and vitamin D
IL -17A is a natural chemical which is important in helping the body defend itself against infection. However, it can make asthma symptoms worse and can reduce the effectiveness of steroid treatment.
In a small study, King's College London researchers checked production of IL-17A in cells from 18 steroid resistant asthma patients and 10 patients who responded to steroids. They also checked results against a group of 10 healthy participants.
The people with asthma had much higher levels of IL-17A than those without asthma. The group with steroid resistant asthma had the highest IL-17A levels.
Further testing suggested vitamin D could significantly reduce production of IL-17A, showing its potential as an additional treatment for asthma and possibly reducing steroid use.
The study was funded by Asthma UK and is published in the Journal of Allergy and Clinical Immunology.
The study was led by Professor Catherine Hawrylowicz from the Medical Research Council and Asthma UK Centre in Allergic Mechanisms of Asthma at King's College London. She says the findings could be very significant: "They are one piece of a big jigsaw puzzle, but we are very excited about them."
"Its experimental data, it needs to go in clinical trials," she cautions.
"We know that a lot of people are vitamin D deficient. We're talking either about a safe sun message, that people need to get outdoors more and get more sun exposure, but obviously within safe limits of not getting burnt.
"Otherwise, maybe they need to consider their diet and eat more oily fish."
The other option is vitamin D supplements. However, Professor Hawrylowicz warns against starting to take a new supplement for asthma without medical advice first. "It's important to ask your doctor," she says.
The next step is reporting on a small clinical trial in people with steroid resistant asthma taking vitamin D supplements, "to see whether it improves their clinical response to steroids."
Professor Hawrylowicz would also like to carry out vitamin D supplement trials in children with severe asthma as well as other groups, "to see whether we can reduce their exacerbations or reduce their medication usage."
She says routine checking of vitamin D levels in people with asthma may need to be considered in future to check for deficiencies.
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