Mika Kivimäki1, Markus Jokela2, Solja T Nyberg3, Archana Singh-Manoux4, Eleonor I Fransson5, Lars Alfredsson6, Jakob B Bjorner7, Marianne Borritz8, Hermann Burr9, Annalisa Casini10, Els Clays11, Dirk De Bacquer11, Nico Dragano12, Raimund Erbel13, Goedele A Geuskens14, Mark Hamer15, Wendela E Hooftman14, Irene L Houtman14, Karl-Heinz Jöckel16, France Kittel10, Anders Knutsson17, Markku Koskenvuo18, Thorsten Lunau12, Ida E H Madsen7, Martin L Nielsen19, Maria Nordin20, Tuula Oksanen3, Jan H Pejtersen21, Jaana Pentti3, Reiner Rugulies22, Paula Salo23, Martin J Shipley15, Johannes Siegrist12, Andrew Steptoe15, Sakari B Suominen24, Töres Theorell25, Jussi Vahtera26, Peter J M Westerholm27, Hugo Westerlund25, Dermot O'Reilly28, Meena Kumari29, G David Batty30, Jane E Ferrie31, Marianna Virtanen3. 1. Department of Epidemiology and Public Health, University College London, London, UK; Faculty of Medicine, University of Helsinki, Helsinki, Finland. Electronic address: m.kivimaki@ucl.ac.uk. 2. Institute of Behavioral Sciences, University of Helsinki, Helsinki, Finland. 3. Finnish Institute of Occupational Health, Helsinki, Tampere and Turku, Finland. 4. Department of Epidemiology and Public Health, University College London, London, UK; Inserm U1018, Centre for Research in Epidemiology and Population Health, Villejuif, France. 5. Institute of Environmental Medicine, Karolinska Institutet, Stockholm, Sweden; School of Health Sciences, Jönköping University, Jönköping, Sweden; Stress Research Institute, Stockholm University, Stockholm, Sweden. 6. Institute of Environmental Medicine, Karolinska Institutet, Stockholm, Sweden; Centre for Occupational and Environmental Medicine, Stockholm County Council, Stockholm, Sweden. 7. National Research Centre for the Working Environment, Copenhagen, Denmark. 8. Department of Occupational Medicine, Koege Hospital, Copenhagen, Denmark. 9. Federal Institute for Occupational Safety and Health (BAuA), Berlin, Germany. 10. School of Public Health, Université libre de Bruxelles (ULB), Brussels, Belgium. 11. Department of Public Health, Ghent University, Ghent, Belgium. 12. Institute for Medical Sociology, Medical Faculty, University of Düsseldorf, Düsseldorf, Germany. 13. Department of Cardiology, West-German Heart Center Essen, University Duisburg-Essen, Essen, Germany. 14. TNO, Hoofddorp, Netherlands. 15. Department of Epidemiology and Public Health, University College London, London, UK. 16. Institute for Medical Informatics, Biometry, and Epidemiology, Faculty of Medicine, University Duisburg-Essen, Essen, Germany. 17. Department of Health Sciences, Mid Sweden University, Sundsvall, Sweden. 18. Department of Public Health, University of Helsinki, Helsinki, Finland. 19. Unit of Social Medicine, Frederiksberg University Hospital, Copenhagen, Denmark. 20. Stress Research Institute, Stockholm University, Stockholm, Sweden; Department of Psychology, Umeå University, Umeå, Sweden. 21. The Danish National Centre for Social Research, Copenhagen, Denmark. 22. National Research Centre for the Working Environment, Copenhagen, Denmark; Department of Public Health and Department of Psychology, University of Copenhagen, Copenhagen, Denmark. 23. Finnish Institute of Occupational Health, Helsinki, Tampere and Turku, Finland; Department of Psychology, University of Turku, Turku, Finland. 24. Department of Public Health, University of Turku, Turku, Finland; Folkhälsan Research Center, Helsinki, Finland; University of Skövde, Skövde, Sweden. 25. Stress Research Institute, Stockholm University, Stockholm, Sweden. 26. Finnish Institute of Occupational Health, Helsinki, Tampere and Turku, Finland; Department of Public Health, University of Turku, Turku, Finland; Turku University Hospital, Turku, Finland. 27. Occupational and Environmental Medicine, Uppsala University, Uppsala, Sweden. 28. Centre for Public Health, Queen's University Belfast, Belfast, UK. 29. Department of Epidemiology and Public Health, University College London, London, UK; Institute for Social and Economic Research, University of Essex, Colchester, UK. 30. Department of Epidemiology and Public Health, University College London, London, UK; Centre for Cognitive Ageing and Cognitive Epidemiology and Alzheimer Scotland Dementia Research Centre, University of Edinburgh, Edinburgh, UK. 31. Department of Epidemiology and Public Health, University College London, London, UK; School of Community and Social Medicine, University of Bristol, Bristol, UK.
Abstract
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. FUNDING: Medical Research Council, Economic and Social Research Council, European Union New and Emerging Risks in Occupational Safety and Health research programme, Finnish Work Environment Fund, Swedish Research Council for Working Life and Social Research, German Social Accident Insurance, Danish National Research Centre for the Working Environment, Academy of Finland, Ministry of Social Affairs and Employment (Netherlands), US National Institutes of Health, British Heart Foundation.
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. FUNDING: Medical Research Council, Economic and Social Research Council, European Union New and Emerging Risks in Occupational Safety and Health research programme, Finnish Work Environment Fund, Swedish Research Council for Working Life and Social Research, German Social Accident Insurance, Danish National Research Centre for the Working Environment, Academy of Finland, Ministry of Social Affairs and Employment (Netherlands), US National Institutes of Health, British Heart Foundation.
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