Researchers have identified a key role for the circadian system—the biological clock that controls your sleep/wake cycle—that may help explain why asthma symptoms worsen at night. The finding sheds light on the mechanisms that influence asthma severity and could lead to new treatments for the condition, they say.
People have observed for decades that asthma symptoms seem to worsen at nighttime. As many as 75% of people with asthma—20 million in the United States--report worsening severity at night. Although many factors influence asthma severity, the role of the circadian system is unclear. It is composed of a central pacemaker located in the brain and additional biological clocks throughout the body and is key for coordinating many bodily functions.
For the study, researchers enrolled 17 people with asthma who were not taking steroids but did use bronchodilator inhalers whenever they felt asthma symptoms were worsening. They divided the participants into two groups. One group spent 38 hours continuously awake in a constant posture with identical snacks every 2 hours, while the other group experienced a 28-hour sleep/wake cycle for one week. Both cycles were conducted under dim lights.
The researchers found that participants in both groups had their lowest lung function during the circadian night (around 4 a.m.) and revealed worsening of asthma during sleep, where it might normally go unnoticed. They also found that use of bronchodilator inhalers was four times more likely during the circadian night than in the day. The study, funded in part by the NHLBI, appears in The Proceedings of the National Academy of Sciences.