Shift work, or work that takes place outside of the traditional 9-to-5 time frame, can be attractive since it offers flexible scheduling and often extra pay, especially for overnight shifts. And for some workers, it’s the only option—especially if they’re working more than one job or taking extra shifts to make ends meet.
But can working a schedule out of tune with your natural circadian rhythm be disruptive to your health? Mounting research says yes, most recently in the form of increasing the risk of high blood pressure.
Researchers at the University of California, Berkeley, followed over 2,100 workers at eight aluminum manufacturing facilities for 10 years. They found that those who worked mostly nights and had frequent rotations (alternating between day and night shifts) during the previous year had a four-fold increased risk of hypertension compared to employees who didn’t work night shifts. Even those who worked a minority of their shifts overnight, or who rotated shifts only rarely, had double the rate of high blood pressure compared to non-night workers. The study was published in the Scandinavian Journal of Work, Environment and Health.
“Our results suggest recent night and rotational work may both be associated with higher rates of incident hypertension,” the authors wrote. They also noted that the overall highest rate of high blood pressure was among “permanent night workers”—those who worked 95 to 100 percent of their hours at night, suggesting that overnight workers experience circadian rhythm disruption even though their work schedules don’t rotate. (A night shift was defined as a shift with at least three hours worked between the hours of 11 p.m. and 6 a.m.)
Earlier research has associated rotating night shift work with a higher risk of cancer in female nurses. In 2007, an agency of the World Health Organization declared that shift work that disrupts a person’s circadian rhythm is “probably carcinogenic” based on animal studies and small population studies in humans.
Bottom line: If you work nights or rotating shifts, be sure to tell your health care provider, and get your blood pressure checked regularly. If you have high blood pressure already and can’t switch jobs or work times, take extra care to stick to your treatment regimen, whether that involves lifestyle steps, medication, or both—or to get treated if you haven’t yet. And consider monitoring your blood pressure regularly at home if you don’t do so already.