Sleep study finds why asthma worsens at night

In the U.S., over 20 million people report experiencing worsening asthma severity at night. Throughout the years, scientists have asked whether it was “simply because of sleep at night or whether our body’s internal clock, our circadian rhythms, may contribute to asthma severity when we are asleep at night?”

New research by Steven A. Shea, Ph.D., Director of our InstituteFrank A.J.L.Scheer, Ph.D., M.Sc. from the Division of Sleep and Circadian Disorders at Brigham and Women’s Hospital and colleagues shows that the internal circadian clock is a significant cause of nocturnal worsening of asthma.

This research involved long-term intensive monitoring of the asthma symptoms, lung function, sleep cycles and circadian rhythms of volunteer participants using three approaches. The first approach assessed variations in asthma severity over 2-3 weeks in the home where any sleep, circadian and environmental factors affecting asthma were all combined, and the other two approaches involved similar assessments but in a laboratory where these factors could be separated. This was achieved by scheduling all behaviors (including lying down, sleep, meals, etc.) and strictly controlling the environment (including constant dim light). Both laboratory protocols revealed that participants with asthma had their lowest lung function during the circadian night, around 4 a.m., and a worsening of asthma that normally may be “hidden” during sleep.

The research has clear clinical significance because the results from the laboratory indicated that that the circadian system caused the symptom-driven bronchodilator inhaler use to be as much as four times greater during the circadian night than during the day. This study provides strong evidence that the internal circadian system plays a major role in the worsening of asthma at night and suggests that our internal body clock time could be considered when treating asthma. The research also points to new questions, including understanding how these circadian system effects on asthma interact with other factors, such as work, exercise and environmental exposures to indoor and outdoor air pollution and allergens (e.g., smoke, pet fur, mold, disinfectants).

Science can continue to advance and impact health when information is shared and disseminated. This important new research has been featured in numerous institutional and media outlets around the U.S. and beyond, including MedscapeU.S. News & World Report, Wired, Brigham and Women’s Hospital and Harvard Medical News. This study ranks in the top 5% of all research outputs scored by Altmetrics.

This research was supported by the National Institutes of Health (grants R01HL064815, R35 HL155681, R01HL118601, M01RR02635, UL1TR002541) and OHSU’s Oregon Institute of Occupational Health Sciences via funds from the Division of Consumer and Business Services of the State of Oregon (ORS 656.630).

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