People who work more than 60 hours a week and frequently go without sleep are at double or treble the risk of suffering a heart attack, a scientific study reveals today.

People who work more than 60 hours a week and frequently go without sleep are at double or treble the risk of suffering a heart attack, a scientific study reveals today.

The stress of long hours and sleep deprivation can increase blood pressure and heart rates to such an extent that chest pains or a cardiac arrest can result, the research suggests.

Scientists, who ran the study in Japan, emphasise the desirability of restricting working hours to 40 or fewer a week. They compared 260 Japanese men, aged 40 to 79, who had survived a first-time heart attack, with 445 men who had no history of cardiac failure.

Details of the men's working week, days off and hours of sleep, over monthly and yearly periods, were analysed. Potential risk factors, including smoking, alcohol intake, weight, and a history of high blood pressure, high cholesterol or diabetes were also recorded.

The results, published in the journal Occupational and Environmental Medicine, showed that the men who had had a heart attack worked longer and were more likely to have had nights of no more than five hours' sleep. In statistical terms, men who worked more than 60 hours a week were twice as likely to have a heart attack, or acute myocardial infarction (AMI). Those who slept five hours a night or less, or had at least two days a week of insufficient sleep, faced a two-fold or threefold increased risk of a heart attack.

Ying Liu, of the National Cancer Centre in Tokyo who led the study, said: "The findings suggest that chronic overwork and sleep deprivation confer increased risk of AMI, and that recent ... sleep deprivation may further enhance the risk of infarction."

The study, between 1996 and 1998, is not the first to reveal the health risks associated with excessive work. In 1977, research in the United Statesshowed that deaths from heart disease rose during periods of economic boom and fell during depressions. Joseph Eyer, who ran that 27-year study, suggested that overtime work peaked in the boom years and caused greater stress.

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