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People who regularly work long hours may be significantly increasing their risk of developing heart disease, the world's biggest killer, British scientists said Monday.
Researchers said a long-term study showed that working more than 11 hours a day increased the risk of heart disease by 67 percent, compared with working a standard 7 to 8 hours a day.
They said the findings suggest that information on working hours -- used alongside other factors like blood pressure, diabetes and smoking habits -- could help doctors work out a patient's risk of heart disease.
However, they also said it was not yet clear whether long working hours themselves contribute to heart disease risk, or whether they act as a "marker" of other factors that can harm heart health -- like unhealthy eating habits, a lack of exercise or depression.
"This study might make us think twice about the old adage 'hard work won't kill you'," said Stephen Holgate, chair of the population and systems medicine board at Britain's Medical Research Council, which part-funded the study.
The study, published in the Annals of Internal Medicine journal, followed nearly 7,100 British workers for 11 years.
"Working long days is associated with a remarkable increase in risk of heart disease," said Mika Kivimaki of Britain's University College London, who led the research. He said it may be a "wake-up call for people who overwork themselves."
"Considering that including a measurement of working hours in a (doctor's) interview is so simple and useful, our research presents a strong case that it should become standard practice," he said.
Cardiovascular diseases such as heart attacks and strokes are the world's largest killers, claiming around 17.1 million lives a year, according to the World Health Organization (WHO). Billions of dollars are spent every year on medical devices and drugs to treat them.
The findings of this study support previous research showing a link between working hours and heart disease.
But the scientists said hard workers should not necessarily be alarmed about their heart health.
"Current evidence on (heart disease) prevention emphasizes the importance of focusing on the total risk, rather than single risk factors," Kivimaki told Reuters Health in an email.
"People who work long hours should be particularly careful in following healthy diets, exercising sufficiently and keeping their blood pressure, cholesterol levels, and blood (sugar) within healthy limits."
The research used data from a study called Whitehall II which has followed the health and wellbeing of more than 10,000 civil service workers in Britain since 1985.
For this study, men and women who worked full time and had no heart disease were selected, giving 7,095 participants.
The researchers collected data on heart risk factors like age, blood pressure, cholesterol, smoking and diabetes and also asked participants how many hours they worked -- including work during the day and work brought home -- on an average weekday.
During the 11-year study, 192 participants had heart attacks. Those who worked 11 hours or more a day were 67 percent more likely to have a heart attack than those with fewer hours.
(Additional reporting by Amy Norton of Reuters Health in New York, editing by Susan Fenton