Long working hours and risk of coronary heart disease and stroke: a systematic review and meta-analysis of published and unpublished data for 603 838 individuals

Background Long working hours might increase the risk of cardiovascular disease, but prospective evidence is scarce, imprecise, and mostly limited to coronary heart disease. We aimed to assess long working hours as a risk factor for incident coronary heart disease and stroke. Methods We identifi ed published studies through a systematic review of PubMed and Embase from inception to Aug 20, 2014. We obtained unpublished data for 20 cohort studies from the Individual-Participant-Data Meta-analysis in Working Populations (IPD-Work) Consortium and open-access data archives. We used cumulative random-eff ects meta-analysis to combine eff ect estimates from published and unpublished data. Findings We included 25 studies from 24 cohorts in Europe, the USA, and Australia. The meta-analysis of coronary heart disease comprised data for 603 838 men and women who were free from coronary heart disease at baseline; the meta-analysis of stroke comprised data for 528 908 men and women who were free from stroke at baseline. Follow-up for coronary heart disease was 5·1 million person-years (mean 8·5 years), in which 4768 events were recorded, and for stroke was 3·8 million person-years (mean 7·2 years), in which 1722 events were recorded. In cumulative meta-analysis adjusted for age, sex, and socioeconomic status, compared with standard hours (35–40 h per week), working long hours (≥55 h per week) was associated with an increase in risk of incident coronary heart disease (relative risk [RR] 1·13, 95% CI 1·02–1·26; p=0·02) and incident stroke (1·33, 1·11–1·61; p=0·002). The excess risk of stroke remained unchanged in analyses that addressed reverse causation, multivariable adjustments for other risk factors, and diff erent methods of stroke ascertainment (range of RR estimates 1·30–1·42). We recorded a dose–response association for stroke, with RR estimates of 1·10 (95% CI 0·94–1·28; p=0·24) for 41–48 working hours, 1·27 (1·03–1·56; p=0·03) for 49–54 working hours, and 1·33 (1·11–1·61; p=0·002) for 55 working hours or more per week compared with standard working hours (ptrend<0·0001). Interpretation Employees who work long hours have a higher risk of stroke than those working standard hours; the association with coronary heart disease is weaker. These findings suggest that more attention should be paid to the management of vascular risk factors in individuals who work long hours

Specific indirect effects for the multiple mediation models.

<p>* <i>P</i> < 0.05</p><p>^n.s.not significant</p><p>Specific indirect effects for the multiple mediation models.</p

Single-level multiple mediation model (1→1→1).

<p>Single-level multiple mediation model (1→1→1).</p

Adjusted Odds Ratios (95% CI) for the Association Between Job Strain and Diabetes (N = 44,818 in All Models), the IPD-Work Consortium, 1984–2003.

<p>Adjusted Odds Ratios (95% CI) for the Association Between Job Strain and Diabetes (N  =  44,818 in All Models), the IPD-Work Consortium, 1984–2003.</p

Participant Characteristics According to Study, the IPD-Work Consortium, 1984–2003.

<p>Participant Characteristics According to Study, the IPD-Work Consortium, 1984–2003.</p

Longitudinal associations between job strain and reducing alcohol intake to moderate or no alcohol, among baseline excessive drinkers (n = 4 981)¹².

1<p>Excessive drinker: an individual who drinks more than recommended amounts of alcohol (intermediate or heavy drinker).</p>2<p>Studies and follow-up times: Belstress (4–7 years), FPS (2–4 years), HeSSup (5 years) and Whitehall II (3–9 years.).</p>3<p>Odds ratios (ORs) from a mixed effects logistic model, adjusted for baseline age, sex and baseline socioeconomic position, with study as the random effect.</p

Participant and study summary.

<p>SD: standard deviation.</p>1<p>Study acronyms: DWECS: Danish Work Environment Cohort Study; FPS: Finnish Public Sector Study; HeSSup: Health and Social Support; HNR: Heinz Nixdorf Recall study; IPAW: Intervention Project on Absence and Well-being; POLS: Permanent Onderzoek Leefsituatie; PUMA: Burnout, Motivation and Job Satisfaction study; WOLF: Work Lipids and Fibrinogen. ² Participants with complete data on job strain, age, sex and socioeconomic position.</p>2<p>Moderate drinking (women: 1–14 drinks/week, men: 1–21 drinks/week); intermediate drinking (women: 15–20 drinks/week, men: 22–27 drinks/week); heavy drinking (women: > = 21 drinks/wk, men: > = 28 drinks/week).</p

Association of alcohol intake and job strain (adjusted for age, sex and socioeconomic position) (N = 142 140).

<p>Association of alcohol intake and job strain (adjusted for age, sex and socioeconomic position) (N = 142 140).</p

Longitudinal associations between job strain at baseline and quitting smoking among baseline smokers (n = 9 975)¹.

1<p>Studies and follow-up times: Belstress (4–7 years), FPS (2–4 years), HeSSup (5 years), SLOSH (1–4 years), WOLF Norrland (3–7 years) and Whitehall II (3–9 years.).</p>2<p>Effect estimates from a mixed effects logistic model, adjusted for baseline age, sex and baseline socioeconomic position, with study as the random effect.</p

Associations of alcohol intake at baseline and job strain at follow-up, stratified by baseline job strain (n = 48 646)¹.

1<p>Studies and follow-up times: Belstress (4–8 years), FPS (2–4 years), HeSSup (5 years) and Whitehall II (3–9 years).</p>2<p>Odds ratios (ORs) from a mixed effects logistic model, adjusted for baseline age, sex and baseline socioeconomic position, with study as the random effect.</p>3<p>Incidence rate ratios (IRRs) from a modified Poisson model, adjusted for baseline age, sex and baseline socioeconomic position, with robust standard errors and study as the cluster variable.</p