People who experience chronic job strain after a first heart attack double their risk of suffering from a second one, according to new research from the Université Laval’s Faculty of Medicine in Quebec.

Previous research had linked work-related stress to a first coronary heart disease event. But this latest study, published in the Oct. 10 issue of the Journal of the American Medical Association, is the first to find conclusive evidence that links stress to a second heart attack as well.

For the study, the research team followed a group of 972 participants, ages 35 to 59, who had suffered a heart attack. Participants were interviewed six weeks, two years and six years after returning to work in order to collect data on their health, lifestyles, socioeconomic status and levels of work stress.

A job was defined as stressful if it combined high psychological demands (heavy workload, intense intellectual activity and important time constraints) and little control over decision-making, including a lack of autonomy, creativity and opportunities to use or develop skills.

During the six-year follow-up period, 124 participants suffered a second heart attack and 82 experienced unstable angina for a total of 206 recurrent events.

People who had reported high levels of stress at work during the first two interviews were twice as likely to fall victim to another event. The risk remained the same even after taking into account factors such as severity of the first heart attack, other health conditions, family history, lifestyle, socioeconomic status, personality and other work-environment characteristics.

The study also found that during the first two years following a heart attack, job strain does not increase the probability of experiencing a second heart attack.

“Employers and occupational health service professionals must find ways to modify the psychological demands of a job or the level of control over decision-making for people returning to work after a heart attack,” concluded study author Chantal Brisson in a news release.