According to a study led by Kentaro Mizuta from Tohoku University Graduate School of Dentistry, melatonin, a sleep hormone, worsens asthma.

The research has been published in the American Journal of Physiology Lung Cellular and Molecular Physiology. Asthma patients suffer from bronchoconstriction, where the smooth muscles of the bronchus, the pathway that moves air to and from your lungs contract. To ease this, many take a bronchodilator, a medicine that widens the bronchus.

However, melatonin, which is often prescribed for insomnia, favoured a state of bronchoconstriction and weakened the relaxing effect of a bronchodilator through the activation of the melatonin MT2 receptor.

To elucidate this, the research group identified the expression of the melatonin MT2 receptor in human airway smooth muscle. They observed that the activation of the melatonin MT2 receptor with higher doses of melatonin or melatonin receptor agonist ramelteon greatly potentiated bronchoconstriction. Furthermore, melatonin attenuated the relaxing effects of the widely used bronchodilator b-adrenoceptor agonist.

"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," said Mizuta.

The first author of the paper Haruka Sasaki added, "The pharmacological therapy that blocks the melatonin MT2 receptor could inhibit the detrimental effects of melatonin on airways."