NEW YORK (Reuters Health) - Men who frequently work long hours or get little sleep are at twice the risk of suffering a non-fatal heart attack, Japanese researchers report.

Since the 1980s, Japanese society has been concerned with a high incidence of sudden deaths occurring amidst a culture of extended work hours, noted Dr. David Snashall, a specialist in occupational medicine at Guy" and St. Thomas's NHS Hospital Trust in London, UK, and an editorial board member of the journal Occupational and Environmental Medicine.

The researchers, led by Ying Liu, a research fellow at the National Cancer Center in Tokyo and a graduate student at Kyushu University in Fukuoka, Japan, conducted a study to investigate whether a link exists between lack of sleep, overtime work and heart attack. The findings of the study, supported by Sankyo, a Japanese pharmaceutical company, are published in the July issue of Occupational and Environmental Medicine.

The researchers evaluated the cases of 260 men aged 40 to 79 who had suffered non-fatal heart attacks between 1996 and 1998. The men were matched to a "control" group of 445 men similar in age and residence who had not had heart attacks.

The researchers compared the number of work hours all the men had put in during the previous year, as well as their average amount of sleep on both days off and work days. They also took into account other possible heart attack risk factors, such as cigarette smoking, alcohol consumption, body weight and disease history.

Men who worked 61 hours a week or more, on average, during the past year were twice as likely to have a heart attack as the men who worked 40 hours a week or less, the investigators found.

And the men who slept for 5 hours or less, on average, each working day during the previous year had twice the heart attack risk of men who got more than 5 hours of sleep nightly.

Also, the researchers found, sleep deprivation in the previous week and lack of more than 2 days off in the previous month boosted heart attack risk even further, suggesting that lack of rest may have a short-term effect as well as a long-term one.

Long hours of work and little sleep are both known to increase blood pressure and heart rate, the authors note. And, they add, the stress of long work hours may throw off the heart's normal rhythm, which can lead to a heart attack.

"These findings suggest that chronic overwork and sleep deprivation confer increased risk of (acute myocardial infarction), and that recent lack of rest and sleep deprivation may further enhance the risk," Liu and colleagues conclude.

The authors state that it would be "desirable" to limit work hours to 40 or less a week, and to ensure that people who do work long hours get enough sleep and take at least 2 days off monthly.

"This gives lots of cause for concern but doesn't prove anything," Snashall commented. "It's a well-executed study where they've proven an association, but they haven't proven that lack of sleep and long working hours are a cause of heart attacks."

SOURCE: Occupational and Environmental Medicine 2002;59:447-451.

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