Excessive overtime raises risk of strokes
Do you work a lot? If your work weeks are longer than normal, you could be more likely of having a stroke, according to a new review.
Swedish researchers found a clear link between long working hours and strokes. Strokes are caused by blood clots or haemorrhages in the brain. The recent meta-analysis was a review of 25 earlier studies covering 600,000 persons in Europe, the USA and Australia.
Professor David Russell of the Oslo University Hospital’s Department of Neurology considers the study highly relevant. He has also conducted research on strokes.
“The study is the strongest evidence we have seen to date that there can be a link between quantities of work and an elevated risk of strokes.”
“This is especially striking because of the magnitude of data from more than 600,000 men and women,” says Dr Russell.
“The mechanism behind this is uncertain, but physical inactivity and stress can be important causes,” he says.
Eleven hours per day
The researchers involved with the new meta-analysis found that the risk rises steadily the more a person works upwards of 40 hours per week.
The risk rose especially among persons who worked more than 11 hours per day, or more than 17.5 hours of overtime per week.
The researchers found that those who worked over 55 hours per week had a 33 percent higher risk of a stroke than ones working normal working hours and weeks of 35-40 hours.
Dangerous stress hormones
The researchers do not know why long working hours are so risky.
“A possible explanation is that persons who have long work days are more stressed. We know that high concentrations of stress hormones can raise the risk of clogged arteries and the development of blood clots which can cause strokes,” said Professor of Epidemiology, Dr Hugo Westerlund to SVT News. He is one of the co-authors of the study.
But the researchers cannot rule out that people who work so much also have higher degrees of other risk factors that are having an impact.
It’s bad to sit still
The researchers made adjustments for physical activity but not for whether the persons working had inactive jobs.
“Inactivity can also be a contributing cause of the higher risk, according to Westerlund, who is the division manager of epidemiology at the University of Stockholm’s Stress Research Institute.
“We now know that it just isn’t enough to be active in your leisure time. One should also avoid long periods [at work] of sitting still,” he says.
The researchers have attempted to make allowances for as many other factors as possible, such as gender, age, medical risk factors and other health issues.
Too much work over a long time is worst
The researchers emphasise that it takes a long time for the risk of a stroke to increase among persons who work long hours.
“If you have lots of work for certain periods, you can avert serious hardening of the arteries by relaxing more. But if you continue at the same pace for a long time, stress can lead to harder arteries. Blood clots can be formed which lead to strokes,” said Töres Theorell, another co-author and a professor emeritus in psychosocial medicine, to SVT.
He recommends people who need to work extremely long days and weeks to make sure they get some solid periods of rest. They should not work more than 55 hours a week for more than two or three weeks at a time.
“Employers should be aware that they can be partly responsible for their employees suffering strokes if they allow them to work terribly much,” said Theorell.
He points out that in addition to the risk for the individual working person, the elevated risk amounts to a big problem for society.
16,000 Norwegians a year have strokes
About 16,000 Norwegians a year have strokes according to Dr Russell at the Oslo University Hospital. Many of these patients suffer new strokes soon afterwards. About 60,000 living Norwegians have had one or more strokes.
Strokes are the major cause of invalidity and hospital admittances and the third most common cause of deaths attributed to disease.
In a broader perspective, strokes are also a prime cause of disease-induced invalidity in the Industrialised West. While billions of dollars are spent rehabilitating patients who have suffered strokes, not enough is spent trying to prevent strokes from occurring in the first place.
Control these risk factors:
Professor Russell thinks it is especially important for people who are overworked to control the following risk factors for strokes:
- Hypertension (high blood pressure),
- Atrial flutter (abnormal heart rhythm),
- High cholesterol,
- Inactive lifestyle,
- Narrowing of the carotid (throat) arteries.
Russell points out that there are many of these risk factors which we can do something about.
Another factor is genetic ― the risk gets higher if someone in the family has had a transient ischaemic attack (minor stroke) or a full stroke.
Read the Norwegian version of this article at forskning.no
Translated by: Glenn Ostling
- 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. 19 August 2015. DOI: http://dx.doi.org/10.1016/S0140-6736(