Staying late at the office for even an hour or two can increase the chances of suffering a stroke, according to research.
Working long hours might impress the boss or even win promotion - but clock-watchers are likely to have the last laugh, a study shows, as they are at less risk of a potentially fatal stroke or heart attack.
Risk level was compared with that of people working a typical 35 to 40-hour week.
Working 41 to 48 hours a week was associated with a 10% risk increase, which rose higher as the hours mounted up. Working 49 to 54 hours pushed up the chances of a stroke by 27% and 55 or more hours raised the risk by a third.
The hardest grafters also experienced a more modest 13% increased risk of heart disease.
Scientists employed a meta-analysis technique to pull together results from 25 studies allowing trends to be seen that may have been previously hidden.
Lead author Professor Mika Kivimaki, from University College London, said: "The pooling of all available studies on this topic allowed us to investigate the association between working hours and cardiovascular disease risk with greater precision than has previously been possible.
"Health professionals should be aware that working long hours is associated with a significantly increased risk of stroke, and perhaps also coronary heart disease."
The findings are published in The Lancet medical journal.
Why working long hours has such an impact on stroke risk remains unclear. The scientists suggest that as well as stress, unhealthy behaviours such as physical inactivity and high alcohol consumption might be involved.
Dr Urban Janlert, from Umea University in Sweden, wrote in the journal: "Long working hours are not a negligible occurrence. Among member countries of the Organisation for Economic Co-operation and Development (OECD), Turkey has the highest proportion of individuals working more than 50 hours per week (43%), and the Netherlands the lowest (less than 1%).
"For all OECD countries, a mean of 12% of employed men and 5% of employed women work more than 50 hours per week.
"Although some countries have legislation for working hours - eg, the EU Working Time Directive gives people the right to limit their average working time to 48 hours per week - it is not always implemented. Therefore, that the length of a working day is an important determinant mainly for stroke, but perhaps also for coronary heart disease, is an important finding."
Dr Mike Knapton, associate medical director at the British Heart Foundation, which part-funded the study, said: "This research shows an association between long working hours and an increased risk of having a stroke and heart disease.
"It is plausible that there could be a causal relationship behind the link as sudden death following long working hours is often caused by stroke, due to long and repeated periods of stress, although that was not demonstrated in this study.
"More research is needed if we are to understand and treat the biological processes that can lead to increased risk of stroke and heart disease for people who work long hours.
"This study highlights to doctors that they need to pay particular attention to cardiovascular risk factors when they advise people who work long hours."