Scientists decode why asthma symptoms get worse at night

Melatonin, the body’s natural hormone linked to the control of the sleep-wake cycle, exasperates the constriction of the pathway that moves air to and from the lungs, according to a new study that explains why asthma patients experience worse symptoms at night.

Several reports indicate that over half of asthma deaths occur at night, suggesting a link between nocturnal asthma symptoms and deaths due to the respiratory condition.

Asthma patients have trouble breathing due to a symptom called bronchoconstriction, where the smooth muscles of the bronchus — the pathway that moves air to and from your lungs — contract. Many patients take bronchodilator medicines in asthma inhalers to widen this air pathway.

While earlier studies have offered explanations for this symptom such as increased exposure to allergens, cooling of the airways, sleeping position, and hormone secretions at night, the exact reason for asthma worsening at night has remained unknown.

Researchers led by Kentaro Mizuta from Tohoku University Graduate School of Dentistry have now discovered that melatonin, a sleep hormone, worsens asthma.

They say the hormone, also taken as an oral drug for the short-term treatment of insomnia such as from jet lag or shift work, favours a state of bronchoconstriction.

The study, published in the American Journal of Physiology Lung Cellular and Molecular Physiology on Saturday, found that melatonin weakens the relaxing effect of a bronchodilator through the activation of the melatonin MT2 receptor protein.

In the study, the researchers identified the expression of the melatonin MT2 receptor in human airway smooth muscle. They found that the activation of the melatonin MT2 receptor with higher doses of melatonin led to the constriction of the bronchus.

The research also found that melatonin reduced the relaxing effects of a class of widely-used bronchodilators that stimulated the β-adrenoceptors.

“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,” Dr Mizuta said in a statement.

“The pharmacological therapy that blocks the melatonin MT2 receptor could inhibit the detrimental effects of melatonin on airways,” Haruka Sasaki, another co-author of the study, added.