The study, conducted by researchers at University College London, found that employees who regularly worked 11-hour days or longer were 67% more likely to develop heart disease than those who worked seven- or eight-hour days. One U.S. expert said many factors could account for the rise in risk among those tied too long to the office.
"Those working long hours may have less time for exercise, healthy eating and physicians visits," said Dr. Gregg C. Fonarow, associate chief of cardiology at UCLA's David Geffen School of Medicine. "They may be exposed to more stress, get less sleep and engage in other behaviors which contribute to cardiovascular risk."
The study, published in the Tuesday issue of the Annals of Internal Medicine, followed a low-risk population of almost 7,100 British civil servants from 1991 until 2004, screening out those with signs of heart disease.
About 70% of the workers were men, and most (91%) were white. Roughly 2.7% developed coronary heart disease by the end of the study, the researchers found.
Participants reported how many hours they spent on the job, including work they took home with them. More than half (54%) put in between seven and eight hours a day, while 21% worked a nine-hour day, and 15% spent 10 hours on the job daily, the study found. Slightly more than 10% labored 11 hours or more.
Besides bumping up the risk for heart disease by 67% compared to people working an eight-hour day, working 11-plus hours a day also put some people into a whole other risk category, the team found.
"Adding working hours to the Framingham risk score improved identification of persons who later developed heart disease," explained study co-author Mika Kivimaki. The Framingham risk score, aimed at gauging heart disease risk, is developed from data that includes age, sex, blood pressure level, cholesterol levels, and whether or not a patient smokes, said Kivimaki, a professor of social epidemiology at University College London.
Still, Kivimaki stressed that her team could not confirm a direct cause-and-effect relationship between putting in lots of overtime and getting heart disease.
Looking at "lifestyle factors," such as time spent working, is an increasing part of heart disease research, noted Dr. Suzanne Steinbaum, a preventive cardiologist at Lenox Hill Hospital in New York City.
"Incorporating long working hours into the (Framingham) model resulted in reclassifying low-risk patients about 4.7% of the time," said Steinbaum, who is also director of Women and Heart Disease at the hospital's Heart and Vascular Institute.
"This is important because patients in a higher-risk category would be treated more aggressively for prevention of coronary heart disease," she said.
Longer working hours are becoming more common in developed countries, the study authors noted, and that could possibly increase workers' odds for coronary heart disease. They added that prior research in Europe and Japan has shown similar links between long work hours and heart attacks, and Kivimaki said "the new information may improve decisions regarding lifestyle interventions and medication for heart disease."
While no changes should be made to patient care at this time, Kivimaki said that if findings were supported by further research, adding questions about working hours to physical exams would be "simple and cost-free."
The kind of work performed can also be important, said Steinbaum. Other research has shown that workers who have little decision-making power or sense of control over their work have a higher risk of getting heart disease, she said.
But this study is just the beginning of the story, said Steinbaum.
Considering new risk factors that are "adding stress to peoples' lives may be well worth contemplating," she said. In that sense, the study is "not the end of the conversation, it's the beginning of one."
