The severity of asthma tends to increase at night, but the extent to which the internal circadian system—as opposed to nocturnal environmental or behavioral factors, such as sleep—contributes to this phenomenon has been unclear.

The researchers assessed variations in asthma severity in 17 patients over 3 weeks at home and in carefully controlled laboratory experiments that dissociated circadian effects from environmental and behavioral effects.

In the 38-hour constant routine protocol, the participants stayed awake in a semirecumbent position and received snacks at fixed intervals.

The 196-hour forced desynchrony protocol consisted of seven sequential 28-hour wake/sleep cycles, with all behaviors scheduled evenly across the circadian cycle.

Pulmonary function followed an endogenous circadian pattern across protocols, with the worst function at night, around 4:00 AM. This result may have clinical relevance because symptom-driven bronchodilator inhaler use was four times more common at night than during the day.

The circadian system and behaviors such as sleep had independent, additive effects on pulmonary function and inhaler use. Taken together, the findings demonstrate that the circadian system has a stand-alone impact on asthma severity.

 According to the authors, the study reveals the potential for improving therapeutic strategies by taking into account individuals’ internal biological time. 

https://www.pnas.org/content/118/37/e2018486118

http://sciencemission.com/site/index.php?page=news&type=view&id=publications%2Fthe-endogenous&filter=22