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Working more than 55 hours a week significantly increases the risk of developing serious heart problems, researchers have found.

People who work such long hours are 40 per cent more likely to suffer an irregular heartbeat than those who work a normal working week of 35 to 40 hours, according to a study.

Long shifts were already known to increase the risk of stroke, but the link with heart rhythm problems - known by the medical term atrial fibrillation - was not previously known.

A study of more than 85,500 British and Scandinavian people found those who worked long hours were far more likely to develop atrial fibrillation over the next decade.

The findings, published in the European Heart Journal, revealed that for every 1,000 people in the study, an extra 5.2 cases of atrial fibrillation occurred among those working long hours.

Atrial fibrillation is the most common heart rhythm disturbance, affecting around one million people in the UK, and can lead to stroke, heart failure and dementia.

Study leader Professor Mika Kivimaki, of University College London, said:
These findings show that long working hours are associated with an increased risk of atrial fibrillation, the most common cardiac arrhythmia.

'This could be one of the mechanisms that explain the previously observed increased risk of stroke among those working long hours.

'Atrial fibrillation is known to contribute to the development of stroke, but also other adverse health outcomes, such as heart failure and stroke-related dementia.
The team found 1,061 new cases of atrial fibrillation occurred during the study - an incidence rate of 12.4 per 1000 people. But among the 4,484 people working over 55 hours the incidence was 17.6 per 1000.

Prof Kivimaki said:
'Those who worked long hours had a 1.4 times higher risk of developing atrial fibrillation, even after we had adjusted for factors that could affect the risk, such as age, sex, socio-economic status, obesity, leisure time physical activity, smoking and risky alcohol use.

'Nine out of 10 of the atrial fibrillation cases occurred in people who were free of pre-existing or concurrent cardiovascular disease.

'This suggests the increased risk is likely to reflect the effect of long working hours rather than the effect of any pre-existing or concurrent cardiovascular disease, but further research is needed to understand the mechanisms involved.

'A 40 per cent increased extra risk is an important hazard for people who already have a high overall risk of cardiovascular disease due to other risk factors such as older age, male sex, diabetes, high blood pressure, high cholesterol, overweight, smoking and physical inactivity, or living with an established cardiovascular disease.

'For a healthy, young person, with few if any of these risk factors, the absolute increased risk of atrial fibrillation associated with long working hours is small.'
Professor Sir Nilesh Samani, medical director at the British Heart Foundation, said: 'The suggestion that longer working hours may be a cause of atrial fibrillation is very interesting.
'Significantly, this study clearly shows that the link between atrial fibrillation and long working hours has nothing to do with the other, already known, risk factors for the condition.'
Dr Tim Chico, consultant cardiologist at the University of Sheffield, added:
'Most people who work long hours won't have the luxury of being able to change their working pattern, and this study does not mean that they should worry that their work is affecting their health.

Comment: What does it mean, then?

'However, we already know that obesity, diabetes, high blood pressure and smoking all increase the risk of AF and so people can reduce their risk by addressing these factors without needing to find another job.'