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Working long hours raises risk of stroke

55-hour working week linked to 33% higher risk of stroke

Adrian O'Dowd

Thursday, 20 August 2015

People who work 55 hours or more per week appear to be 33% more likely to have a stroke and 13% more likely to develop coronary heart disease compared to those working a standard 35-40 hour week, according to a study* published today in The Lancet.

Previous studies have suggested that long working hours play a part in causing heart disease, but limitations of these studies could have biased the results.

Therefore, Mika Kivimäki, professor of epidemiology at University College London, and colleagues carried out a systematic review and meta-analysis of published studies and unpublished individual-level data examining the effects of longer working hours on cardiovascular disease up to 20 August 2014.

In what is described as the largest study in this field so far, the researchers analysed data from 25 studies involving 603,838 men and women from Europe, the USA, and Australia. The participants were followed for an average of 8.5 years.

The researchers found a 13% increased risk of incident coronary heart disease (a new diagnosis, hospitalisation, or death) in people working 55 hours or more per week compared with those putting in a normal 35 to 40 hour week, even after taking into account risk factors including age, sex, and socioeconomic status.

Analysis of data from 17 studies involving 528,908 men and women who were followed up for an average of 7.2 years, found a 1.3 times higher risk of stroke in individuals working 55 hours or more a week compared with those working standard hours.

The association was still the case even after taking into account health behaviours such as smoking, alcohol consumption, and physical activity, as well as cardiovascular risk factors including high blood pressure and high cholesterol.

The researchers found that the longer people worked, the higher their chances of a having a stroke.

The authors said that although the causal mechanisms of these relationships needed to be better understood, they suggested that increasing health-risk behaviors, such as physical inactivity and high alcohol consumption, might increase the risk of stroke.

Professor Kivimäki said: “The pooling of all available studies on this topic allowed us to investigate the association between working hours and cardiovascular disease risk with greater precision than has previously been possible.

“Health professionals should be aware that working long hours is associated with a significantly increased risk of stroke, and perhaps also coronary heart disease.”

Writing in a linked comment,** Dr Urban Janlert from Umeå University in Sweden, said: “Although some countries have legislation for working hours – e.g. the EU Working Time Directive gives people the right to limit their average working time to 48 hours per week – it is not always implemented.

“Therefore, that the length of a working day is an important determinant mainly for stroke, but perhaps also for coronary heart disease, is an important finding.”

Dr Mike Knapton, associate medical director at the British Heart Foundation, said: “More research is needed if we are to understand and treat the biological processes that can lead to increased risk of stroke and heart disease for people who work long hours.

“This study highlights to doctors that they need to pay particular attention to cardiovascular risk factors when they advise people who work long hours."


* Prof Mika Kivimäki, et al. Long working hours and risk of coronary heart disease and stroke: a systematic review and meta-analysis of published and unpublished data for 603 838 individuals. The Lancet, 2015. DOI: 10.1016/S0140-6736(15)60295-1

** Urban Janlert. Long working hours: an avoidable cause of stroke? The Lancet, 2015. DOI: 10.1016/S0140-6736(15)61000-5

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