The finding, from an 11-year study of 6,000 British civil servants, does not provide definitive proof that long hours cause coronary heart disease but it does show a clear link, which experts said may be due to stress.
In all, there were 369 cases of death due to heart disease, non-fatal heart attacks and angina among the London-based study group -- and the risk of having an adverse event was 60 percent higher for those who worked three to four hours overtime.
Working an extra one to two hours beyond a normal seven-hour day was not associated with increased risk.
"It seems there might a threshold, so it is not so bad if you work another hour or so more than usual," said Dr Marianna Virtanen, an epidemiologist at the Finnish Institute of Occupational Health and University College London.
The higher incidence of heart problems among those working overtime was independent of a range of other risk factors including smoking, being overweight or having high cholesterol.
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New York Times