Working long hours may up risk of second heart attack

Long working hours of ≥55 hours/week is associated with an excess risk of recurrent coronary heart disease (CHD) events compared with the average 35–40 work hours/week among people who return to work after surviving a heart attack, a longitudinal study finds.

“Looking at long working hours and job stressors was helpful in determining how hostile a working environment was and how much potential stress a participant could be under,” said lead author Dr Xavier Trudel from The CHU de Quebec-Universite Laval Research Center in Quebec, Canada. “Once both factors are introduced, there’s a noticeable increase in the risk of recurrent CHD events.”  

Heart attack survivors who worked long hour (≥55 hours/week) were 67 percent more likely than their counterparts with 35–40-hour work week, after extensive adjustment for sociodemographics, clinical risk factors, lifestyle-related risk factors, personality factors, and work environment factors (adjusted hazard ratio [HR], 1.67, 95 confidence interval [CI], 1.10–2.53). [J Am Coll Cardiol 2021;77:1616-1625]

“The magnitude of the observed association is comparable to that of current smoking [HR, 1.70], an acknowledged risk factor for recurrent CHD events,” noted the researchers.

Furthermore, a spline regression model showed that the longer the overtime hours, the greater the risk of recurrent CHD events. For each 10 hours additional overtime hour on top of the reference level of 40 hour/week, the HR of a recurrent CHD rose from 1.2 for a 50-hour work week, to 1.5, 1.92, 2.46, 3.1, and 3.78 for 60, 70, 80, 90, and 100 work hours/week, respectively. 

Specifically, overtime workers who also faced high levels of job strain were particularly at risk of a recurrent CHD event. Among individuals who worked ≥55 hours/week, the HR of a recurrent CHD event was 2.55 in those who faced high job strain compared with 1.34 in those with no job strain. Work with high psychological demands and low decision control was classified as high job strain.

“This could be attributable to the deleterious effect of prolonged exposure to work stressors among those working longer hours,” explained Trudel and co-authors. “[Alternatively,] changes in lifestyle habits may be implicated … previous studies have shown that people working long hours have a higher prevalence of smoking, physical inactivity, and alcohol consumption.”

The prospective cohort study enrolled 967 adults aged 35–59 years who returned to work following their first myocardial infarction (MI). They were followed on recurrent CHD events, which included fatal/nonfatal MI and unstable angina over an average of 5.9 years. Participants were classified into four categories based on their weekly working hours: part-time (21–34 hours/week), full-time (35–40 hours/week), low overtime (41–54 hours/week), and medium/high overtime (≥55 hours/week). 

Analysing the participants characteristics, the researchers found that those who worked medium/high overtime hours were more likely to be men than women (10.7 percent vs 1.9 percent), younger, and poorer lifestyle (smoking, drinking, and sedentary habits).

“The study provides a new piece of research evidence that work-related factors play an important role in coronary heart disease prognosis,” wrote Professor Li Jian from University of California, Los Angeles in Los Angeles, California, US in a linked commentary. “Occupational health services are urgently needed to be incorporated into secondary prevention of cardiovascular disease.” [J Am Coll Cardiol 2021;77:1626-1628]

“Long working hours should be assessed as part of early and subsequent routine clinical follow-up to improve the prognosis of post-MI patients,” said Trudel.