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Original Research |

Using Additional Information on Working Hours to Predict Coronary Heart Disease: A Cohort Study

Mika Kivimäki, PhD; G. David Batty, PhD; Mark Hamer, PhD; Jane E. Ferrie, PhD; Jussi Vahtera, MD, PhD; Marianna Virtanen, PhD; Michael G. Marmot, MD, PhD; Archana Singh-Manoux, PhD; and Martin J. Shipley, MSc
[+] Article and Author Information

From University College London, London, United Kingdom; University of Turku and Turku University Hospital, Turku, Finland; Finnish Institute of Occupational Health and University of Helsinki, Helsinki, Finland; and Institut National de la Santé et de la Recherche Médicale, Paris, France.


Financial Support: By the Medical Research Council; British Heart Foundation; Wellcome Trust; Health and Safety Executive; Department of Health; Agency for Health Care Policy and Research; John D. and Catherine T. MacArthur Foundation Research Networks on Successful Midlife Development and Socioeconomic Status and Health; National Heart, Lung, and Blood Institute and National Institute on Aging of the National Institutes of Health; Academy of Finland; NEW OSH ERA Research Programme; and European Science Foundation. Drs. Kivimäki and Vahtera are supported by the Academy of Finland, Dr. Batty is a Wellcome Trust Fellow, Dr. Ferrie is supported by the Medical Research Council, Dr. Marmot is a Medical Research Council professor, Dr. Singh-Manoux is supported by a European Young Investigator Award from the European Science Foundation, and Mr. Shipley is supported by the British Heart Foundation.

Potential Conflicts of Interest: Disclosures can be viewed at www.acponline.org/authors/icmje/ConflictOfInterestForms.do?msNum=M10-2252.

Reproducible Research Statement:Study protocol: Not available. The design of the Whitehall II study is available at www.ucl.ac.uk/whitehallII/study-phases. Statistical code: Not available. Data set: Available on application to the Whitehall II study data sharing policy at www.ucl.ac.uk/whitehallII/data-sharing.

Corresponding Author: Mika Kivimäki, PhD, Department of Epidemiology and Public Health, University College London, 1-19 Torrington Place, London WC1E 6BT, United Kingdom; e-mail, m.kivimaki@ucl.ac.uk.

Current Author Addresses: Drs. Kivimäki, Batty, Hamer, Ferrie, and Marmot and Mr. Shipley: Department of Epidemiology and Public Health, University College London, 1-19 Torrington Place, London WC1E 6BT, United Kingdom.

Dr. Vahtera: University of Turku and Turku University Hospital, Lemminkäisenkatu 14-18 B, FI-20520 Turku, Finland.

Dr. Virtanen: Finnish Institute of Occupational Health and University of Helsinki, Topeliuksenkatu 41 aA, FI-00250 Helsinki, Finland.

Dr. Singh-Manoux: Institut National de la Santé et de la Recherche Médicale, 101 rue de Tolbiac, 75654 Paris Cedex 13, France.

Author Contributions: Conception and design: M. Kivimäki, M. Hamer, J. Vahtera, M. Virtanen, M.G. Marmot.

Analysis and interpretation of the data: M. Kivimäki, G.D. Batty, J.E. Ferrie, J. Vahtera, M. Virtanen, M.G. Marmot, A. Singh-Manoux, M.J. Shipley.

Drafting of the article: M. Kivimäki, G.D. Batty, M. Hamer, J.E. Ferrie.

Critical revision of the article for important intellectual content: M. Kivimäki, G.D. Batty, M. Hamer, J. Vahtera, M. Virtanen, M.J. Shipley.

Final approval of the article: M. Kivimäki, G.D. Batty, M. Hamer, J.E. Ferrie, J. Vahtera, M. Virtanen, A. Singh-Manoux, M.J. Shipley.

Provision of study materials or patients: A. Singh-Manoux.

Statistical expertise: M.J. Shipley.

Obtaining of funding: M. Kivimäki, M.G. Marmot.

Administrative, technical, or logistic support: M. Kivimäki.

Collection and assembly of data: J.E. Ferrie, M.G. Marmot, A. Singh-Manoux, M.J. Shipley.


Ann Intern Med. 2011;154(7):457-463. doi:10.7326/0003-4819-154-7-201104050-00003
Text Size: A A A

Background: Long working hours are associated with increased risk for coronary heart disease (CHD). Adding information on long hours to traditional risk factors for CHD may help to improve risk prediction for this condition.

Objective: To examine whether information on long working hours improves the ability of the Framingham risk model to predict CHD in a low-risk, employed population.

Design: Cohort study with baseline medical examination performed between 1991 and 1993 and prospective follow-up for incident CHD performed until 2004.

Setting: Civil service departments in London (the Whitehall II study).

Participants: 7095 adults (2109 women and 4986 men) aged 39 to 62 years working full-time without CHD at baseline.

Measurements: Working hours and the Framingham risk score were measured at baseline. Coronary death and nonfatal myocardial infarction were ascertained from medical screenings every 5 years, hospital data, and registry linkage.

Results: 192 participants had incident CHD during a median 12.3-year follow-up. After adjustment for their Framingham risk score, participants working 11 hours or more per day had a 1.67-fold (95% CI, 1.10- to 2.55-fold) increased risk for CHD compared with participants working 7 to 8 hours per day. Adding working hours to the Framingham risk score led to a net reclassification improvement of 4.7% (P = 0.034) due to better identification of persons who later developed CHD (sensitivity gain).

Limitation: The findings may not be generalizable to populations with a larger proportion of high-risk persons and were not validated in an independent cohort.

Conclusion: Information on working hours may improve risk prediction of CHD on the basis of the Framingham risk score in low-risk, working populations.

Primary Funding Source: Medical Research Council; British Heart Foundation; Bupa Foundation; and the National Heart, Lung, and Blood Institute and National Institute on Aging of the National Institutes of Health.

Figures

Grahic Jump Location
Appendix Figure.
Study flow diagram.

CHD = coronary heart disease.

Grahic Jump Location

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