Working more than 60 hours a week and a regular lack of sleep may double the risk of having a heart attack, according to new research published today.
The study looked at 260 Japanese men aged between 40 and 79 who had been admitted to hospital for a first time heart attack but survived.
They were compared with another group of 445 men with no history of heart attack.
The researchers obtained details of the men's weekly working hours, number of days off and amount of sleep within the last month and during the past year.
They also looked at potential risk factors for heart attack, including lifestyle, weight and conditions such as high blood pressure, high cholesterol and diabetes.
The results showed that men working more than 60 hours a week faced double the risk of a heart attack when compared with those who worked 40 hours or less each week.
Sleeping an average of five or less hours a night and having a frequent lack of sleep, defined as two or more days a week of under five hours, were also associated with a doubling or tripling of the risk.
In particular frequent lack of sleep and fewer days off in the preceding month also significantly increased the chances of having a heart attack.
The study, which ran from 1996 to 1998, is featured in the journal Occupational and Environmental Medicine, published by the British Medical Association.
"Overtime work is known to increase blood pressure and heart rate, and induce cardiac or psychological symptoms - such as chest pain, depression and fatigue," the study, by the National Cancer Centre in Tokyo, states.
"It is also known that a lack of sleep increases activity in the sympathetic nervous system, leading to an increase of blood pressure and heart rate."
They suggest that the combination of the two could increase sympathetic nervous system activity to the point where it triggers a heart attack.
They conclude that the optimal working week is a maximum of 40 hours and those who work longer should ensure they get enough sleep and have at least two days rest a month.
PA