Sleep Health | Sleep Review
For hundreds of years, people have observed that the severity of asthma often worsens at night. A long-standing question is to what extent the body’s internal circadian clock – as opposed to behaviors such as sleep and physical activity – contributes to the worsening of asthma severity. Using two circadian protocols, researchers from Brigham and Women’s Hospital and Oregon Health & Science University identified the impact of the circadian system and uncovered a key role for the biological clock in asthma. Understanding the mechanisms that affect asthma severity could have important implications for both the study and management of asthma. The results are published in The Proceedings of the National Academy of Sciences.
“This is one of the first studies to carefully isolate the impact of the circadian system from other behavioral and environmental factors, including sleep,” says co-author Frank AJL Scheer, PhD, MSc, director of the Medical Chronobiology Program in the Sleep Division – and circadian disorders at Brigham, in a press release. Corresponding author Steven A. Shea, PhD, professor and director at the Oregon Institute of Occupational Health Sciences added, “We have observed that the people with the worst asthma are generally those who suffer from the most circadian-induced lung wastes in the function Night and also had the greatest changes induced by behaviors, including sleep. We also found these results to be clinically important as the symptom-driven use of bronchodilators on the circadian night was up to four times more common on the circadian night than during the day when it was tested in the laboratory. “
Up to 75% of people with asthma report experiencing worsening asthma severity at night. Many behavioral and environmental factors, including exercise, air temperature, posture, and sleeping environment, are known to influence the severity of asthma. Scheer, Shea, and colleagues wanted to understand the contribution of the internal circadian system to this problem. The circadian system consists of a central pacemaker in the brain (the suprachiasmatic core) and “clocks” throughout the body and is crucial for the coordination of body functions and for anticipating the daily environmental and behavioral demands of cycling.
To decouple the influence of the circadian system from sleep and other behavioral and environmental factors, the researchers enrolled 17 participants with asthma (who did not speak steroid drugs but used bronchodilator inhalers when they felt worsening asthma symptoms) in two supplemental laboratory protocols, where lung function, symptoms of asthma and use of bronchodilators were continuously assessed. In the “Constant Routine” protocol, participants spent 38 hours uninterruptedly awake, in a constant posture and in low light with identical snacks every two hours. In the “forced desynchronicity” protocol, participants were placed in a recurring 28-hour sleep-wake cycle under low light conditions for a week, with all behaviors evenly distributed over the cycle.
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