A long hours office culture can affect more than just your social life – long days at work can be bad for your heart as well, according to a major study.

It’s been established that too many hours in the office can increase the risk of a stroke. Now it seems that clocking up more than 55 hours a week means a 40% higher chance of developing an irregular heartbeat, known as atrial fibrillation (AF), when compared to those with a better work-life balance.

AF happens because the natural electrical impulses controlling the heart’s normal regular rhythm lose their co-ordination. Sufferers may get palpitations – the sensation of a racing or irregular pulse – as well as feeling breathless and dizzy.

But some people with AF get no symptoms at all, which is why the British Heart Foundation encourages people to check whether their pulse is regular and to see a GP if they have any doubts. It’s important to diagnose AF because it increases the chance of having a stroke five-fold, and blood thinning treatments can greatly lower this risk.

The research team, led by Professor Mika Kivimaki from the department of epidemiology at University College, London, analysed data on the working patterns of 85,494 mainly middle-aged men and women drawn from the UK, Denmark, Sweden and Finland.

Participants were put into groups according to their work pattern, with 35-40 hours a week regarded as the control group. No one had AF at the start of the study, published in the European Heart Journal.

After 10 years of follow-up, an average of 12.4 per 1,000 people had developed AF, but among those working 55 hours or more, this figure was higher at 17.6 per 1,000 people.

Those working the longest hours were more overweight, had higher blood pressure, smoked more and and consumed more alcohol. But the team’s conclusions about longer working hours and AF still remained after taking these factors into account.

The researchers acknowledge some limitations to their study: they only asked participants about working hours at the start, and so couldn’t account for how working patterns might have changed over 10 years. The team also could not tell whether any particular job type was more risky.

Kivimaki offered worried workers some reassurance. “For a healthy person, the risk of AF is very low, and a 1.4-fold increase in that small risk due to long working hours does not much change the situation.”

Tim Chico, a Sheffield cardiologist not involved with the study also had some helpful advice for those concerned that their job might harm their heart: “Most people who work long hours won’t have the luxury of being able to change their working patterns. We already know that obesity, diabetes, high blood pressure and smoking all increase the risk of AF and so people can reduce their risk of AF by addressing these factors without needing to find another job!”