”Sunshine vitamin 'may treat asthma'”, BBC News informs us, as a new lab-based study suggests vitamin D could help control symptoms of severe asthma.
Asthma is caused by inflammation of the airways, related to malfunctioning of the body’s immune system. In theory, the immune system mistakes harmless substances, such as dust mites, as a threat and triggers inflammation of the lungs and airways (which causes the symptoms of asthma).
The study in question looked at IL-17A, which is one of the molecules thought to be associated with the malfunctioning immune response seen in asthma. Researchers examined whether vitamin D had an effect on the levels of the molecule produced by white blood cells in a laboratory experiment.
Researchers found that vitamin D reduced the levels of IL-17A produced by cells from people with asthma. This included cells from people who had previously failed to respond to the treatment of choice for severe asthma – oral corticosteroids – often referred to as steroids.
While this study suggests that vitamin D can have an effect on IL-17A levels in the laboratory, it is certainly too early to hail vitamin D as a potential “cure” for asthma. A positive effect on cells in the lab does not guarantee vitamin D supplements will improve symptoms for people with asthma. Clinical trials in people with asthma are ongoing to test whether this will be the case.
The study was carried out by researchers from King’s College London; Queen Mary, University of London, and the Homerton University NHS Foundation Trust. It was funded by Asthma UK and the National Institute for Health Research, and some researchers received Medical Research Council Funding. The study was published in the peer-reviewed Journal of Allergy and Clinical Immunology.
This study was reported by the BBC, Daily Mail, and the Daily Express. The BBC correctly points out that treating asthma patients with vitamin D “has not yet been tested”. The main text of the Mail’s coverage is generally accurate, although their headline suggests that “Vitamin D ‘helps beat the symptoms of asthma’”, when this was not assessed by the study. The Express’s coverage over-interprets the results by suggesting that “Soaking up sun could be a cure for asthma” or could be “the best way of treating asthma”.
This was a laboratory study looking at the effect of vitamin D on one type of white blood cell (T helper cells called TH17 cells) from people with asthma.
One type of T helper cell called TH2 is known to be involved in inflammation of the airways in asthma. However, some evidence suggests that other T cells may also play a role.
TH17 cells are involved in defending the body against bacterial and fungal infections. There is some evidence that these cells may be involved in severe asthma. Also, one of the inflammatory substances produced by these cells, called IL-17A, may exacerbate asthma and reduce patients’ ability to respond to standard treatment for severe asthma – oral corticosteroids (steroids).
Previously, studies had shown that vitamin D could influence the T cells from patients with severe asthma, and also affect TH17 cells. The researchers in the current study wanted to see if vitamin D affected IL-17A production by TH17 cells collected from asthma patients. They also wanted to see whether this effect was different in people who were resistant to steroid treatments.
The researchers took blood from 10 healthy adults and 28 patients with moderate to severe asthma and extracted white blood cells, including T cells. The patients had to have had diagnosed asthma for at least six months. Of the patients, 18 had asthma that did not respond as well to oral steroid treatment (steroid resistant asthma), and 10 had asthma that responded to steroids.
The researchers grew the white blood cells in the laboratory, either with or without vitamin D and the steroid dexamethasone, and looked at how much IL-17A was being produced. They assessed whether this varied between people with and without asthma, or in people with steroid resistant asthma.
White blood cells from people with asthma produced higher levels of IL-17A than those from non-asthmatic patients. Furthermore, white blood cells from people with steroid resistant asthma produced the highest levels of IL-17A.
Treating the white blood cells with vitamin D reduced the production of IL-17A. This reduction occurred in cells from people with steroid-resistant asthma and steroid-sensitive asthma, and was not affected by adding the steroid dexamethasone.
The researchers concluded that their results support the hypothesis that vitamin D could improve disease control in people with asthma by reducing IL-17A levels, regardless of whether the person’s asthma is steroid-resistant.
The current laboratory study suggests that vitamin D can reduce white blood cell production of an inflammatory molecule implicated in asthma.
These results were obtained from cells in the laboratory, and further research will be needed to determine whether this effect will also be seen if people with asthma are given vitamin D.
While the results perhaps give a reason to investigate vitamin D further, not all treatments showing initially positive results in laboratory studies go on to have a positive effect on real-world clinical outcomes.
The good news is, as the Daily Mail reports, the results of this study are being followed up with a randomised controlled trial in participants with steroid resistant asthma.
Randomised controlled trials are the best way of testing if treatments are effective. This trial, and others, will tell us if vitamin D works as a treatment for asthma and if so, who it might be effective at treating.