Working long hours increases the risk of developing a dangerous irregular heartbeat, British research shows.
Scientists compared people who work 35 to 40 hours a week with hard grafters who labour for 55 hours or more.
Over 10 years, the harder workers were 40 per cent more likely to suffer the condition known as atrial fibrillation (AF).
Statistical analysis showed that for every 1000 participants, an extra 5.2 cases of AF occurred among those working long hours.
Results from the study of 85,500 men and women from the UK, Denmark, Sweden and Finland are reported in the European Heart Journal.
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"These findings show that long working hours are associated with an increased risk of atrial fibrillation, the most common cardiac arrhythmia," said lead researcher Professor Mika Kivimaki, of University College London.
"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."
Atrial fibrillation raises the risk of having a stroke because it causes blood to pool and form clots.
Professor Sir Nilesh Samani, medical director of the British Heart Foundation, said: "Although we know some of the causes of atrial fibrillation, such as age, high blood pressure, heart valve disease and excess alcohol consumption, many patients develop the condition without an obvious cause.
"The suggestion that longer working hours may be a cause of atrial fibrillation is very interesting.
"More research is needed to understand and prove what's behind this association."
