Attention all workaholics. The latest research finds that people working 10 or 11 hours a day are more likely to suffer serious heart problems, including heart attacks, than those clocking off after seven hours.

The findings published in The European heart Journal are from an 11-year study of 6,000 British civil servants. 369 of these people died from heart disease or had heart attacks or angina. Those who worked three to four hours overtime each day had a 60 percent higher risk of developing these problems. The researchers say this shows a clear link between long hours and heart disease, which experts say may be due to stress.

On the other hand, working an extra hour or two beyond a normal day didn’t increase risk. Researchers think there might a threshold, that a little extra doesn’t hurt. They also say it’s possible the lifestyle of people working long hours deteriorated over time, for example as a result of poor diet or increased alcohol consumption.

More fundamentally, long hours may be associated with work-related stress, which interferes with metabolic processes, as well as “sickness presenteeism,” whereby employees continue working when they are ill.