Fifteen million people may unintentionally be putting themselves at risk for future strokes. New animal research suggests that the 20% of Americans who regularly work the graveyard shift see long-lasting effects on their sleep-wake cycle. The effects persist even after returning to a normal sleep schedule.
The sleep-wake cycle is governed by an internal biological clock that prepares the body when to sleep, eat, and more. Daylight also influences your biological clock, acting as a cue when to stay awake and suppressing hormones that promote drowsiness. Hospital workers, nurses, and night security guards are among the many with disrupted biological clocks.
“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,” says David Earnest, a professor at the Texas A&M University College of Medicine and study author in a statement. “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.”
Previous research has investigated the health impacts of irregular sleep schedules. In one animal study, sleep schedules meant to mimic rotating shift work schedules increased the number of strokes. Animals were regular 24-hour cycles of day and night, in contrast, did not show signs of brain damage or functional deficits. Males had the worst outcomes. Those with disrupted schedules had a higher mortality rate than females with disrupted sleep schedules.
The current study decided to look past the immediate effects of shift work on strokes. Instead, they focused on how shift work affected people in the long term and when they returned back to a normal sleep-wake schedule. They evaluated their risk of stroke when they reached midlife — the equivalent of when humans start to experience a stroke.
“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,” says Earnest. “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?”
Results confirmed that the effects of shift work continue to influence one’s health years after. For one thing, the sleep-wake cycle of animals on ‘shift-work schedules’ never returned to normal compared to the rats kept on a regular day-night schedule. Researchers also observed periods of abnormal activity when sleep should have happened. Animals with irregular schedules were prone to strokes. Although, females were more likely to have severe brain impairments and a higher risk of dying than their male counterparts.
“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,” explains Farida Sohrabji, a professor in the Department of Neuroscience and Experimental Therapeutics and director of the Women’s Health in Neuroscience Program.
Another observation was increased levels of inflammatory mediators from the gut in animals on a shift-work schedule. One suggestion the researchers propose is that the connection between stroke and disrupted biological clocks may have to do with how the brain and gut communicate with each other.
Shift workers can help care for their internal body clocks by keeping a regular sleep-wake schedule as much as possible. Additionally, not drinking, not smoking, and avoiding diets high in fat may also help reduce inflammation and the risk of stroke.
The results may also give insight into the health outcomes of people who tend to stay up late at night. “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,” says Earnest. “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.”
The study is published in the journal Neurobiology of Sleep and Circadian Rhythms.