Shift work leads to more severe strokes, study says

Shift work disrupts circadian rhythm cycles, which can lead to more severe ischemic strokes, according to an experimental study in rats reported online June 2, 2016 in the journal Endocrinology.

“Circadian rhythm disturbances, or desynchronization, are known to occur in response to shift work, jet lag, and even workplace or social influences that commonly impose highly irregular schedules on our sleep-wake patterns, mealtimes, and other health-related processes,” the authors wrote.

Compared with animals on a normal day/night schedule, those on shift work schedules had more severe stroke outcomes in both brain damage and loss of sensation and limb movement, the researchers found.

Interestingly, outcomes were different in males and females. Males on shifted day/night cycles had shorter survival times and extremely high rates of mortality compared with males on a normal schedule. In females, the major effect of a shift work schedule was that it exacerbated stroke severity, increasing infarct volume and sensorimotor deficits.

“These sex differences might be related to reproductive hormones,” said study co-author Farida Sohrabji, PhD, a Professor in the Department of Neuroscience and Experimental Therapeutics, and Director of the Women’s Health in Neuroscience Program at Texas A&M Health Science Center College of Medicine, in College Station, TX.

The researchers also found that, in female rats, a shift work schedule abolished the estrous cycle, which resulted in constant estrus and elevated levels of circulating estradiol.

Dr. Sohrabji drew a comparison to humans from this finding in rats. “Young women are less likely to suffer strokes compared with men of a similar age, and when they do, the stroke outcomes are likely to be less severe,” she explained. “In females, estrogen is thought to be responsible for this greater degree of neuroprotection.”

By the same token, older women approaching menopause show increasing incidence of ischemic stroke and poor prognosis for recovery compared with men at the same age, she noted.

Other research on circadian rhythm disturbances in humans lend credence to the findings from this study, particularly in regard to vascular disease. Among women in the Nurses’ Health Study, the risk of cardiovascular disease was higher for those who had worked rotating night shifts compared with those who did not work night shifts, the researchers noted. Another study found that male shift workers in Sweden had significantly increased stroke- and cardiovascular-related mortality (although not overall mortality).

Factors that alter circadian rhythm can dramatically increase inflammatory responses, which may lead to cardio- and cerebrovascular disease, the researchers suggested.

“Next, we would like to explore whether inflammation is a key link between circadian rhythm disruption and increased stroke severity,” said study co-author David Earnest, PhD, also a professor in the Department of Neuroscience and Experimental Therapeutics at Texas A&M. “With this information, we may be able to identify therapeutic interventions that limit damage after a stroke in patients with a history of shift work.”

Until then, people on shift work-type schedules should be monitored more closely and more frequently for cardio- and cerebrovascular disease and risk factors, such as hypertension and obesity, Dr. Earnest suggested.