Working long hours—particularly 46 hours per week or more—may increase the long-term risk of cardiovascular disease (CVD) events such as heart attack.

That’s the conclusion of a study in the March Journal of Occupational and Environmental Medicine, official publication of the American College of Occupational and Environmental Medicine.

"In general, we found that the risk of CVD increased as average weekly working hours increased," writes Sadie H. Conway, PhD, of University of Texas Health Sciences Center, Houston, and colleagues.

They note that among full-time workers, CVD risk appears lowest between 40 and 45 hours per week.

The researchers analyzed the relationship between work hours and CVD using data on more than 1,900 participants from a long-term follow-up study of work and health.

All participants had been employed for at least 10 years.

Overall risk was increased by 35% for those who worked 60 hours per week.
During the study, a physician-diagnosed CVD event—angina, coronary heart disease or heart failure, heart attack, high blood pressure, or stroke—occurred in about 43% of participants.

Findings and Implications

Risk of CVD events increased by 1% for each additional hour worked per week over at least 10 years, after adjustment for age, sex, racial/ethnic group, and pay status.

The difference was significant only for full-time workers, not part-timers. Among those who worked more than 30 hours per week, risk increased as weekly hours approached 40, but then decreased again between 40 and 45 hours per week.

Beginning at 46 hours, increasing work hours were progressively associated with increased risk of CVD.

Compared to people who averaged 45 hours per week for 10 years or longer, overall CVD risk was increased by 16% for those who worked 55 hours per week and by 35% for those who worked 60 hours per week.

While previous research has suggested increased CVD risk with longer working hours, the new study is the first to show a "dose-response" effect.

Conway cautions employers and workers to avoid interpreting the study as showing a clear causal relationship between long work hours and CVD.

“Based on this study alone, we cannot conclude that long work hours cause CVD. Nor can we conclude that individuals working more than 46 hours per week are at a certain level or risk for CVD,” she says.

Rather, Conway advises, evidence from the study should be considered in light of other research on work hours and CVD, which, she says, has generally shown a relationship between long work hours and CVD outcomes, although the findings are not universal.

A relationship between working long hours and CVD risk is biologically plausible.
“Given what we know about the mechanisms underpinning CVD, a relationship between working long hours and CVD risk is biologically plausible,” she explains, emphasizing that more research is necessary “before clinicians could begin making specific recommendations regarding work hours relative to CVD risk.”

She acknowledges, however, that her research is a step toward that goal.

“This study provides specific evidence on long work hours and an increase in the risk of CVD, thereby providing a foundation for CVD prevention efforts focused on work schedule practices,” she said.

Long Work Hours and Related Health Risks

Conway notes that poor health behaviors, such as decreased exercise, poor dietary choices, and increased smoking have been shown to be associated with working long hours.

And typically, she says, sleep deprivation and stress come with the territory.

“We also know that individuals working long hours tend to have less time to rest and recover from work and, thus, generally sleep fewer hours or have lower quality sleep than individuals who work fewer hours," she said.

“Further, job stress has been suggested as a risk factor for CVD, although the influence of stress on disease development seems to depend on many factors.”

She adds that although her study was not able to evaluate the impact of lifestyle choices or sleep quality or duration, “We do encourage individuals to reduce their risk of CVD by making health-promoting choices (such as exercising regularly and eating a healthy diet) and by decreasing—as much as possible—stress in their lives."