Stroke risk: For whom the bell tolls

26. October 2015

Those who work 55 hours or more per week increase their risk of stroke by up to 33 percent. The authors of a recently published meta-analysis have come to this conclusion after evaluating data including 528,908 men and women from Europe, USA and Australia.

For their Meta-analysis, the group, led by Professor Mika Kivimäki of the Department of Epidemiology and Public Health at University College London, UK, evaluated published and unpublished data. This data included 528,908 men and women from 24 cohorts in Europe, USA and Australia. After accounting for confounding factors such as age, gender and socioeconomic status, the researchers concluded that compared to normal working hours of 35-40 hours per week, working longer hours increases the relative risk of stroke by up to a third. The researchers found a dose-response relationship: when working 41-48 hours per week, the risk of stroke increased by 10%, working 49-54 hours weekly caused a 27% increase and 55 hours or more resulted in a 33% increase.

The weaknesses of the epidemiologic study include the fact that the work was based on a self-assessment questionnaire completed just once. In addition, there could be – as with all observational studies – other confounding factors, such as workload or sleep time. Nevertheless, the authors believe the results of their analysis to be meaningful: “The consideration of all available studies on this topic allowed us to analyse the relationship between weekly working hours and cardiovascular risk with greater accuracy than was previously possible”, declared Prof. Kivimäki. “Health professionals should also be aware that long working hours are associated with a significantly increased risk of stroke and possibly an increased risk of CHD”.

Individual risk vs. Population risk

Stroke and heart attack are multifactorial diseases whose genesis is characterised by many interacting risk factors. These include, for example, sport, nutrition, obesity, smoking and stress, all of which are known to have a significant impact on cardiovascular risk. Nevertheless, the newly-discovered effect of working hours should not be neglected. “Even if the 30% increase in the risk is quite low for a single person, people should remember this anyway” says Professor Urban Janlert from Umeå University in Sweden, in an Editorial for Lancet study. Similarly, the lead author of the Lancet: “People who work long hours should be especially careful to maintain a healthy lifestyle and to make sure that blood pressure and lipids are in the normal range”, says Prof. Kivimäki.

But the responsibility does not lie with the individual worker alone – politics and society also have a role to play. “The main problem is the public health aspect – even if the individual risk is not alarming, the high number of people working long hours will result in more strokes in the overall population” warns Prof. Janlert. Unlike other unfavorable health conditions, which lie in the nature of work and are difficult to change, such as shift work, noise exposure or extreme temperatures, the duration of a working day can be a conscious decision. “Basically, the following applies: If long working hours pose a hazard to health, it should be possible to change them”, says Prof. Janlert in the Lancet editorial.

Workaholics are in vogue

In the EU working time is governed by Directive 2003/88/EC, Member States are obliged to regulate the working week so that an average working time of 48 hours per week (including overtime) is not exceeded. But the reality for many workers is different. In Europe, the number of people working long hours varies dramatically from country to country: People work for the longest in Turkey – the proportion of people who spend more than 50 hours a week at work is 40.9%. In the Netherlands, the figure is only 0.4% and 2% in Denmark. The average across OECD countries is 13%.

Looking for cause and effect

In terms of the reasons why an above average working week is associated with an increased stroke risk, the authors of the Lancet study can only speculate. But there are basically two conceivable paths: firstly, a high number of working hours has a negative impact on the time available for the body to regenerate. Secondly, long working hours are often accompanied by unhealthy behaviours such as smoking, coffee/alcohol consumption, an unhealthy diet and lack of exercise. Of course, both insufficient regeneration as well as lifestyle factors could be at fault simultaneously.

For this reason, says Prof. Janlert in the Editorial to the Lancet study, experimentally results need to be verified and intermediate mechanisms such as stress response, blood pressure and sleep duration must be examined. He is convinced that: “The consequences of long working hours and not the long hours alone are the underlying cause of the results obtained by Kivimäki and colleagues”. Be that as it may, it is up to us to bear this newly identified risk factor in mind.


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Dr Madhav Manikal
Dr Madhav Manikal

An important variable in this should be the TYPE of Work- whether sitting at an office desk most of the time as is now common with electronic/technology/computer/ robotic/ remote-control techno advances vs. physical muscular work. ?

#2 |

Did researchers take into consideration the difference between mental and physical labor?

#1 |

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