According to a new study, living against our biological clocks can harm our long-term health by altering gut-brain interactions.
While most Americans are getting ready for bed, 15 million people are just getting started. These health care workers, emergency workers, industrial operators and others are among the 20 percent of the world’s population who work shifts. Their irregular sleep-wake cycle increases the risk of various health problems, including diabetes, heart attacks, cancer and strokes.
However, shift work may have worse consequences than we previously thought. According to a recent study published in the journal Neurobiology of sleep and circadian rhythmsthe negative effects of shift work can persist for a long time, even after returning to a regular schedule.
“Shift work, especially shift work, messes up our clocks, and that has important implications in terms of our health and well-being and the relationship to human disease,” said David Earnest, a professor in the Department of Neurology and Experimental Therapeutics at the University of Texas College of Medicine. A&M. “When our internal body clocks are synchronized correctly, they coordinate all of our biological processes to occur at the correct time of day or night. When our body clocks are out of alignment, whether due to shift work or other disruptions, it leads to changes in physiology, biochemical processes, and various behaviors.
Ernst and colleagues found that animal models with rotating shift work schedules had worse stroke outcomes in terms of both brain damage and functional impairment than those with typical 24-hour day-night cycles. Men fared much worse, with significantly higher death rates.
This innovative research uses a novel approach. Instead of looking at the immediate impact of shift work on strokes, the researchers switched all individuals back to typical 24-hour cycles and waited until their middle-age equivalent — when people are most likely to have a stroke — to assess stroke severity and outcomes .
“What’s already borne out in the epidemiologic studies is that most people only work shifts for five to eight years and then probably go back to normal work schedules,” Earnest said. “We wanted to determine if this is enough to erase all the problems that these circadian rhythm disturbances have, or do these effects carry over even after returning to normal work schedules?”
They found that the health effects of shift work did persist over time. The sleep-wake cycles of subjects on shift work schedules never truly returned to normal, even after subsequent exposure to a regular schedule. Compared to controls maintained on a regular day-night cycle during the study, they showed persistent changes in their sleep-wake rhythm, with periods of unusual activity when sleep would normally occur. When they suffered strokes, their outcomes were again much worse than the control group, except that women had more severe functional deficits and higher mortality than men.
“The data from this study take on additional health implications, particularly for women, as stroke is a risk factor for dementia and disproportionately affects older women,” said Farida Sohrabji, professor in the Department of Neurology and Experimental Therapeutics and director of the Program “Women’s Health in the Neurosciences.”
The researchers also observed increased levels of inflammatory mediators from the gut in subjects exposed to shift work schedules. “We now think that part of the underlying mechanism for what we’re seeing in terms of disruption of the circadian rhythm causing more severe strokes may involve altered interactions between the brain and the gut,” Earnest said.
The results of this study could ultimately lead to the development of interventions that block the adverse effects of disrupted circadian rhythms. Meanwhile, shift workers can improve the care of their internal body clocks by trying to maintain a regular schedule as much as possible and avoiding a high-fat diet, which can cause inflammation and also alter the timing of circadian rhythms.
This research has clear implications for shift workers, but may extend to many other people who maintain schedules that vary widely from day to day.
“Because of the computer age, many more of us no longer work nine to five. We take our work home and sometimes work late into the night,” said Ernest. “Even those of us who work regularly tend to stay up late on weekends, creating what’s known as ‘social jet lag’, which similarly winds our clocks so they no longer keep the correct time.” All of these can lead to the same effects on human health as shift work.’
To avoid some of these health hazards, Earnest says the best approach is to maintain a regular schedule of wake times, sleep times, and meal times that don’t vary drastically from day to day. Also, avoid common cardiovascular risk behaviors such as eating a high-fat diet, not being physically active, drinking too much alcohol, and smoking.
Reference: “Gender Differences in the Diathetic Effects of Shift Work Schedules on Circulating Cytokine Levels and Pathological Outcomes of Midlife Ischemic Stroke” by David J. Ernest, Shaina Burns, Sivani Pandey, Kathiresh Kumar Mani and Farida Sohrabjee, 30 June 2022, Neurobiology of sleep and circadian rhythms.
The study was funded by the National Institutes of Health.