Up to three quarters of people with asthma report that their symptoms get worse at night, a phenomenon noted as far back as the 17th century – however, the reasons why have remained unclear. New research puts some of the blame on circadian rhythms rather than behavior or environment alone.
There are many plausible explanations for why asthma might worsen during the night, including falling temperatures and lying down. The treatments in these cases might be very different than if the observations are mainly attributable to internal biological clocks.
Professor Frank Scheer of Bringham and Women's Hospital and Professor Steven Shea of the Oregon Institute of Occupational Health Sciences co-led a study to try to distinguish between possible causes. In Proceedings of the National Academy of Sciences, they and co-authors report that in a small sample, the stronger someone's circadian rhythm, the more likely they are to experience a major increase in asthma symptoms when ready to sleep.
The researchers had people who were not taking steroid medication – but were using bronchodilator inhalers when experiencing asthma symptoms – adjust their sleep patterns to disrupt their biological clocks.
One group shifted to a 28-hour wake/sleep cycle, sustained for one week under constant lighting, quickly putting them out of sync with day and night conditions. The others stayed awake for 38 hours under dim light while eating every two hours. Inevitably this wasn't good for any of the participants, but some suffered more than others.
When on a normal 24-hour cycle, the participants' asthma was worst on waking and shortly before sleep. However, on the 28-hour cycle, asthma became most severe at the equivalent of 4:00 AM (ie 20-22 hours after waking). On the one hand, people will sleep through mild breathing difficulties and so may not notice this peak. On the other, deaths from asthma are most common at night, so symptoms at those hours shouldn't be ignored.
“This is one of the first studies to carefully isolate the influence of the circadian system from the other factors that are behavioral and environmental, including sleep,” Scheer said in a statement.
Shea added; “We observed that those people who have the worst asthma in general are the ones who suffer from the greatest circadian-induced drops in pulmonary function at night, and also had the greatest changes induced by behaviors, including sleep.”
This has immediate implications for treatment, Shea noted. “When studied in the laboratory, symptom-driven bronchodilator inhaler use was as much as four times more often during the circadian night than during the day.”
The authors don't think circadian rhythms are the whole story, pointing to previous evidence for other factors playing a role. However, if our natural body clocks make an important contribution, that's something we need to know in a world where asthma rates are rising. However, a sample size larger than 17 may be necessary to really confirm the claim.