Long working hours and health in office workers: a cohort study of coronary heart disease, diabetes, depression and sleep disturbances.
Doctoral thesis, UCL (University College London).
This thesis examined the association between long working hours and health outcomes with high public health relevance; coronary heart disease (CHD), type 2 diabetes, depression and sleep disturbances, in a cohort of middle-aged white-collar British civil servants. Earlier research has shown mixed results on the topic but the evidence relies largely on cross-sectional and case-control studies. I used data from the longitudinal Whitehall II study where self-reported working hours were assessed at phase 3 (1991-1993) when the employed participants were 39 to 61 years of age. The second assessment of working hours was at phase 5 (1997-1999). CHD was assessed at phases 3, 5, and 7 (2003-04); type 2 diabetes at phases 3 and 7; depression at phases 3 and 5, and sleep disturbances at phases 3, 5, and 7. Analyses of each outcome disorder were based on a cohort free from the specific disorder at baseline. Follow-up time ranged between 6 to 11 years depending on the outcome, and the number of participants in each part of the study ranged between 913 and 6014 depending on the baseline and follow-up data available. Incidence of CHD was indicated by CHD death, non-fatal myocardial infarction and angina defined on the basis of clinical examinaton, clinical records, and nitrate medication use. Type 2 diabetes was ascertained from high fasting or postload plasma glucose levels, self-reported information on doctor-diagnosed diabetes and use of medication assessed during clinical examinations. Onset of depression was assessed by University of Michigan version of Composite International Diagnostic Interview (UM-CIDI) and onset of sleep disturbances were requested by survey questions on sleep length and four types of sleep disturbances (the Jenkins Scale). Several known confounding and mediating covariates were assessed and included in the analyses. Working 11-12 hours per day (or >55 hours per week) at baseline, compared with working 7-8 hours per day (or 35-40 per week) was associated with an increased risk of CHD, depression and most types of sleep disturbances at follow-up. Working long hours was not associated with an increased incidence of type 2 diabetes except among prediabetic participants. These findings were robust to adjustments for relevant confounding factors at baseline. The results of this thesis indicate that long working hours could be recognized as a potential risk marker for the development of CHD, depression, and sleep disturbances. However, the results are generalisable to British white-collar workers only, and as this study is based on observational data it is not known whether the associations are causal.
|Title:||Long working hours and health in office workers: a cohort study of coronary heart disease, diabetes, depression and sleep disturbances|
|Open access status:||An open access version is available from UCL Discovery|
|UCL classification:||UCL > School of Life and Medical Sciences > Faculty of Population Health Sciences > Institute of Epidemiology and Health Care > Epidemiology and Public Health|
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