Long working hours may lead to stroke

By Eleanor McDermid, Senior medwireNews Reporter

Working long hours may increase people’s risk of having a stroke, shows a meta-analysis published in The Lancet.

“Our findings suggest that more attention should be paid to the management of vascular risk factors in individuals who work long hours”, say Mika Kivimäki (University College London, UK) and study co-authors.

The risk of stroke was elevated 33% in people who worked 55 or more hours per week compared with those who worked 35 to 40 hours per week, and this was highly statistically significant (p=0.002). The findings were independent of age, gender and socioeconomic status.

There was even a significant dose-response for stroke, with stroke being elevated 10% (nonsignificant), 27% and 33% among people working 41 to 48 hours, 49 to 54 hours and 55 or more hours, respectively.

In an accompanying commentary, Urban Janlert (Umeå University, Sweden) says: “Because coronary heart disease is more prevalent than stroke in people of working age, this finding is an interesting one that has probably been missed because of the smaller populations studied previously.”

There was also an association with coronary heart disease risk, but the 13% risk increase was smaller than that for stroke, it was less strongly statistically significant (p=0.02) and there was no dose-response.

The current meta-analysis included 25 published and unpublished prospective cohort studies from 11 countries. These studies provided data on 528,908 men and women who had 1722 strokes during an average follow-up of 7.2 years and 603,838 who had 4768 coronary events during an average 8.5 years of follow-up.

The team found no evidence of reverse causation (ie, patients reducing their hours after having a stroke), and findings were unaffected by the extent of adjustment for confounding, the method of ascertaining outcomes and whether studies were published or unpublished.

In a press statement, Tim Chico, consultant cardiologist from the University of Sheffield, UK, noted that a causal relationship would be very difficult to prove, and, in any case, it can be extremely hard for people to reduce their working hours.

But he noted that people working long hours could still make changes to reduce their cardiovascular risk. “We should all consider how the working environment could be altered to promote healthy behaviour that will reduce strokes, irrespective of how long we work.”

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