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Could the Sleep Hormone Melatonin Worsen Asthma?

ASTHMA is a long-term condition affecting over 5 million people in the UK. Symptoms include coughing, wheezing, chest tightness, and shortness of breath. For many patients with asthma, these symptoms often get worse at night, which is known as ‘nocturnal asthma’. For a long time, it has been a mystery why symptoms get worse at night, and the exact mechanisms behind this process are unknown. With over 50% of asthma deaths occurring at night, this is an important link to understand, and now a novel study has finally uncovered why asthma symptoms might get worse at night. 

This fascinating study, led by Kentaro Mizuta, Tohoku University, Japan, examined the expression of the melatonin MT2 receptor in smooth airway muscle in humans. The scientists found that the activation of this receptor with higher doses of melatonin or ramelteon (a melatonin receptor agonist) considerably increased bronchoconstriction. 

In other words, melatonin, the sleep hormone, potentiated the constriction of the airways, and consequently worsened asthma symptoms at night. 

Melatonin is occasionally prescribed to treat insomnia, and promotes the constriction of the bronchus, which allows air to travel to and from the lungs. Some asthma patients take bronchodilators to help with the constriction of the bronchus; however, melatonin activates the melatonin MT2 receptor, weakening the effect of the bronchodilator.  

Mizuta summarised the findings of the study: “Although serum concentration of melatonin did not significantly induce the airway constriction, greater doses of melatonin, which is clinically used to treat insomnia, jet lag, or cancer, worsened asthma symptoms and impaired the therapeutic effect of bronchodilators.”  

This new discovery will help doctors become aware of how prescribing high doses of melatonin for patients with asthma, for the treatment of insomnia or other conditions, can be extremely harmful. Finally, the authors of the study concluded that future work could include novel drug treatment targeting the blockage of the melatonin MT2 receptor to prevent the harmful effects of melatonin on the constriction of the bronchi.