According to a new study, living against our biological body clocks might harm our long-term health by changing gut and brain interactions.
While most Americans are getting ready to sleep, 15 million individuals are just getting started. These healthcare employees, emergency responders, industrial operators, and others are among the 20 percent of the world’s population that work shifts. Their irregular sleep-wake cycle raises their risk of a variety of health problems, including diabetes, heart attacks, cancer, and strokes.
However, shift work might have worse consequences than we previously believed. According to a recent study published in the journal Neurobiology of Sleep and Circadian Rhythmsthe negative consequences of shift work might last for a long time, even after returning to a regular schedule.
“Shift work, especially rotating shift work, confuses our body clocks and that has important ramifications in terms of our health and well-being and connection to human disease,” said David Earnest, Professor in the Department of Neuroscience and Experimental Therapeutics at the Texas A&M University College of Medicine. “When our internal body clocks are synchronized properly, they coordinate all our biological processes to occur at the right time of day or night. When our body clocks are misaligned, whether through shift work or other disruptions, that provides for changes in physiology, biochemical processes and various behaviors.”
Earnest and colleagues discovered animal models with rotating shift work schedules had worse stroke outcomes in terms of both brain damage and functional impairments than those with typical 24-hour cycles of day and night. Males had far worse outcomes, with substantially higher fatality rates.
This innovative research took a new approach. Rather than 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 midlife equivalent — when people are most likely to have a stroke — to assess stroke severity and outcomes.
“What was already born out in epidemiological studies is that most people only experience shift work for five to eight years and then presumably go back to normal work schedules,” Earnest said. “We wanted to determine, is that enough to erase any problems that these circadian rhythm disruptions have, or do these effects carry over even after returning to normal work schedules?”
They found that the health impacts of shift work do, indeed, 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 throughout the study, they displayed persistent alterations of their sleep-wake rhythms, with periods of abnormal activity when sleep would have normally occurred. When they suffered strokes, their outcomes were again much worse than the control group, except females had more severe functional deficits and higher mortality than the males.
“The data from this study take on added health-related significance, especially in females, because stroke is a risk factor for dementia and disproportionately affects older women,” said Farida Sohrabji, Professor in the Department of Neuroscience and Experimental Therapeutics and director of the Women’s Health in Neuroscience Program.
The researchers also observed increased levels of inflammatory mediators from the gut in subjects exposed to a shift work schedule. “We now think that part of the underlying mechanism for what we’re seeing in terms of circadian rhythm disruption causing more severe strokes may involve altered interactions between the brain and gut,” Earnest said.
The results of this study could eventually lead to the development of interventions that block the adverse effects of disrupted circadian rhythms. In the meantime, shift workers can improve care of their internal body clocks by trying to maintain a regular schedule as much as possible and avoiding a diet high in fat, which can cause inflammation and also alter the timing of circadian rhythms.
This research has clear implications for shift workers, but it could extend to many other people who keep schedules that differ greatly from day to day.
“Because of the computer age, many more of us are no longer working from nine to five. We take our work home and sometimes work late at night,” Earnest said. “Even those of us who do work regular schedules have a tendency to stay up late on the weekends, producing what is known as ‘social jet lag,’ which similarly unwinds our body clocks so they no longer keep accurate time. All this 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 awake time, sleep time, and mealtimes that doesn’t vary drastically from day to day. In addition, avoid the usual cardiovascular risk behaviors like eating a high-fat diet, not getting enough physical activity, drinking too much alcohol, and smoking.
Reference: “Sex differences in the diathetic effects of shift work schedules on circulating Cytokine levels and pathological outcomes of ischemic stroke during middle age” by David J. Earnest, Shaina Burns, Sivani Pandey, Kathiresh Kumar Mani and Farida Sohrabji, 30 June 2022, Neurobiology of Sleep and Circadian Rhythms.
The study was funded by the National Institutes of Health.