Researchers at Children's Hospital of Philadelphia (CHOP) have found that circadian rhythms, or the body's internal biological clocks, can affect outcomes related to influenza infections. The study, published in the Journal of Clinical Investigation, suggests that understanding and managing these rhythms could help clinicians improve care for patients with respiratory viral infections.
Circadian rhythms are internal processes that follow a roughly 24-hour cycle and help organisms adapt to environmental changes. Each organ and cell has its own clock regulated by these rhythms. While it is commonly known that disruptions such as shift work or jet lag can affect alertness and sleep patterns, it is less widely recognized that the state of a person's circadian rhythm can also influence how they respond to infections.
Light exposure and meal timing act as "zeitgebers," or external cues, which synchronize with internal clocks in organs and cells to support optimal function. Previous research from the same team showed that certain times of day are linked to better immune responses against viruses like influenza. However, it was unclear whether maintaining these external cues after infection would continue to provide protection.
"Since influenza affects patients over a period of several days, we were able to test how zeitgebers like light influence this time-of-day-specific protection even after the host sustains the infection," said senior study author Shaon Sengupta, MBBS, MPH, an attending neonatologist in the Division of Neonatology at CHOP whose research focuses on circadian rhythms. "We suspected that sustaining exposure to these rhythmic external cues helps maintain this level of protection after an infection."
The researchers used a preclinical model to examine how disrupting environmental lighting affected immune response during a critical window following infection. They found that breaking normal light cycles eliminated the protective effect seen at certain times of day in earlier studies. This disruption led to abnormal immune activity, including accumulation of inflammatory cells in the lungs during upper respiratory infection. However, keeping meal schedules consistent reduced some negative effects caused by disrupted light cycles. This suggests external cues like regular meals may compensate when other body clocks are disturbed.
"Our findings are of particular relevance for hospitalized patients, since circadian disruption due to erratic light-cycling or meal timing are rather prevalent in such settings," Sengupta said. "Our data suggest that circadian health of the host is a critical determinant of outcomes and may be modified by well-timed environmental cues with potential to drive outcomes in severe respiratory viral infection. Beyond mechanistic insights, our study calls for incorporating circadian-sensitive practices on hospital floors and intensive care units. These may include, but are not limited to, light-cycling and meal-timing interventions as strategies to bolster immune response and hasten recovery."
The research received funding from National Institutes of Health grants R01HL155934-01A1 and NHLBI R01HL147472 as well as support from the Raine Medical Research Foundation.
