Working long hours (> 55 hours per week) linked to an increased risk of MI and stroke.

According to this article in the Lancet this week, working long hours can increase risk of coronary artery disease events by a factor of 13% (relative risk, 1.13) and the risk of stroke by 33% (relative risk, 1.33). The researchers adjusted for exercise and hypertension in the analysis but did not adjust for sleep quantity or quality, an omission that may be significant, as any worker working days and occasional second job nights and physicians whose long hours of work are added to significantly by sleep-interrupting night call may know.

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ABSTRACT

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working hours and risk of coronary heart disease and stroke: a systematic review and meta-analysis of published and unpublished data for 603 838 individuals

Prof Mika Kivimäki, PhDcorrespondenceemail, Markus Jokela, PhD, Solja T Nyberg, MSc, Archana Singh-Manoux, PhD, Eleonor I Fransson, PhD, Prof Lars Alfredsson, PhD, Prof Jakob B Bjorner, MD, Marianne Borritz, MD, Hermann Burr, PhD, Annalisa Casini, PhD, Els Clays, PhD, Prof Dirk De Bacquer, PhD, Prof Nico Dragano, PhD, Prof Raimund Erbel, MD, Goedele A Geuskens, PhD, Mark Hamer, PhD, Wendela E Hooftman, PhD, Irene L Houtman, PhD, Prof Karl-Heinz Jöckel, Prof France Kittel, PhD, Prof Anders Knutsson, MD, Prof Markku Koskenvuo, MD, Thorsten Lunau, MSc, Ida E H Madsen, PhD, Martin L Nielsen, MD, Maria Nordin, PhD, Tuula Oksanen, MD, Jan H Pejtersen, PhD, Jaana Pentti, MSc, Prof Reiner Rugulies, PhD, Prof Paula Salo, PhD, Martin J Shipley, MSc, Prof Johannes Siegrist, PhD, Prof Andrew Steptoe, DSc, Prof Sakari B Suominen, MD, Prof Töres Theorell, MD, Prof Jussi Vahtera, MD, Prof Peter J M Westerholm, MD, Prof Hugo Westerlund, PhD, Dermot O'Reilly, PhD, Prof Meena Kumari, PhD, G David Batty, DSc, Jane E Ferrie, PhD, Prof Marianna Virtanen, PhD for the IPD-Work Consortium

Published Online: 19 August 2015

Open AccessArticle has an altmetric score of 175

DOI: http://dx.doi.org/10.1016/S0140-6736(15)60295-1 |

Summary

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 identified 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-effects meta-analysis to combine effect 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 different 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.

Image credit: ACP (acpinternist.org)

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