Working an extra three hours a day will raise your chance of early death

The study found that people who regularly work ten or 11 hours a day could be up to 60 per cent more likely to suffer heart problems and to die.

Campaigners said the research raised further questions about the effects of people's working lives on their heath.

The latest study, published in the European Heart Journal, followed more than 6,000 people, concluding that working overtime is bad for the heart.

The men and women aged between 39 and 61 who took part in the study, all working as civil servants in the UK, were followed for an average of 11 years.

The researchers assessed their risk of suffering a heart attack or angina, or developing heart disease that led to them dying.

They found 369 cases where people suffered heart disease that caused death, had a heart attack or developed angina.

Even when factors such as age and whether people were overweight or smoked were taken into account, overtime was linked to a 56 to 60 per cent increased risk of heart disease or dying compared with people who did not do overtime.

The increased risk was linked to working between three and four hours extra a day on top of a normal seven-hour day.

Marianna Virtanen, an epidemiologist at the Finnish Institute of Occupational Health in Helsinki and University College London, said: "Our findings suggest a link between working long hours and increased coronary heart disease (CHD) risk, but more research is needed before we can be confident that overtime work would cause CHD."

The researchers said there could be a number of explanations for the possible link between overtime and heart problems. These include "hidden" high blood pressure that is not always picked up, stress, anxiety or depression, and being a "Type A" personality who is highly driven, aggressive or irritable.

People who do not sleep for enough hours or have "insufficient time" for winding down after work before bed may also see their risk increased.

They added: "Employees who work overtime may also be likely to work while ill – that is, be reluctant to be absent from work despite illness."

In an editorial commenting on the research, Gordon McInnes, from Glasgow University, said the study appeared to reinforce the notion that work stress linked to overtime was associated with heart disease.

"If the effect is truly causal, the importance is much greater than commonly recognised," he said. "Overtime-induced work stress might contribute to a substantial proportion of cardiovascular disease."

David Clark, Chest, Heart and Stroke Scotland's chief executive David Clark, said: "It's clear that putting unreasonable pressure on people at work isn't good for their health, including their cardiovascular health. However, the study doesn't make it clear whether this was in fact the case, or whether there were other confounding variables which, as suggested, may have been responsible for the apparent increase in cardiovascular risk."

The British Heart Foundation said the study raised further questions about how working lives could influence the risk of heart disease.

Cathy Ross, BHF senior cardiac nurse, said: "Although the researchers showed a link between working more than three hours overtime every day and heart problems, the reasons for the increased risk weren't clear.

"The researchers suggest a number of reasons – 'hidden' high blood pressure, reduced sleeping hours and stress. These may affect the mechanisms that cause heart disease, but it could simply be that working long hours means we've less time to look after ourselves."