Of the participants, 3256 (54%) did not usually work overtime, 1247 (21%) worked approximately one, 894 (15%) two, and 617 (10%) three or four extra hours a day. Table presents associations between baseline covariates and overtime working hours. Participants working overtime were slightly younger than participants not working overtime. Men, married, or cohabitating participants and those in higher occupational grades worked overtime more often than women, non-married/co-habited, or lower-grade participants. Absence of pre-existing diabetes, smoking history, and alcohol use exceeding recommended limits were also associated with overtime work. More of those working overtime reported daily fruit and vegetable consumption and more exercise, but shorter sleeping hours and less sickness absence days. They also reported higher prevalence of psychological distress and higher scores on measures of type A behaviour, job demands, and decision latitude at work than individuals not working overtime. Overtime work was associated with lower HDL cholesterol levels compared with employees with no overtime work. After Bonferroni correction of the P-values, the significant heterogeneity in baseline characteristics between worktime groups (Table ) remained largely unchanged. The only exceptions were the differences in age and sleeping hours which became non-significant after adjusting for multiple testing (corrected values: P = 0.08 for age and P = 0.15 for sleeping hours).
Characteristics of the participants by daily overtime hours at baseline: the Whitehall II study
Table shows the association of overtime with incident CHD. Altogether there were 67543.9 person-years of follow-up during which 369 new events of CHD occurred, resulting in a rate of 5.46 events per 1000 person-years. In the model adjusted for sociodemographic factors (Model A), working 3 or 4 h (but not 1 or 2 h) of overtime was associated with incident CHD (HR 1.60, 95% CI 1.15–2.23, P = 0.005), compared with no overtime work. The Bonferroni corrected P-value for the excess CHD risk in this overtime category was P = 0.015 and the association changed little after further adjustment for all potential CHD risk factors (Models B to E). The largest reduction in effect size (16%) was found after adjustment for health behaviours (Model C). Of these, smoking and body mass index were related to incident CHD. An 11% effect size reduction was found after adjustment for type A behaviour pattern (Model E). The hazard ratio for incident CHD for scores in the top tertile of type A behaviour was 1.46 (95% CI 1.09–1.95, P = 0.011).
Association between exposure to overtime work at baseline and incident coronary heart disease, as indicated by coronary death, incident non-fatal myocardial infarction, or incident definite angina pectoris: the Whitehall II study
We repeated the analyses with the outcome defined as fatal CHD and new non-fatal MI, but excluding definite angina pectoris (Table ). In the model adjusted for socio-demographic characteristics, working 3–4 h of overtime (but not 1 or 2 h) was associated with incident fatal CHD or non-fatal MI (HR 1.90, 95% CI 1.17–3.06, P = 0.009) when compared with employees with no overtime work (Model A). The Bonferroni corrected P-value for this hazard ratio was P = 0.027. Again, the largest reduction in the hazard ratio was found after adjustment for health behaviours (19%, Model C) and type A behaviour pattern (12%, Model E). Of these covariates, smoking, alcohol use (lower risk with high alcohol use when compared with no use), and body mass index were independently associated with the outcome, and the hazard ratio for scores in the top tertile of type A behaviour pattern was HR 1.43 (95% CI 0.93–2.20, P = 0.10).
Association between exposure to overtime work at baseline and incident coronary heart disease, as indicated by coronary death or incident non-fatal myocardial infarction: the Whitehall II study
In order to examine the effect of depressive symptoms on the association between long working hours and CHD, we re-ran Model E using the depression subscale of the GHQ38
and leaving out psychological distress as a covariate. We found no significant difference in the results (3–4 h overtime work was associated with incident CHD including definite angina, HR 1.56, 95% CI 1.11–2.20; P
= 0.010 with incident fatal CHD, non-fatal MI or definite angina, HR 1.71, 95% CI 1.04–2.81 with incident fatal CHD, non-fatal MI or definite angina, P
To examine whether the association between long working hours and CHD was dependent on socioeconomic position or work stress factors, we tested interaction effects. No interaction was found between occupational grade or job demands and working hours (P-values 0.50 and 0.41 for coronary death, incident non-fatal MI, or definite angina pectoris; P-values 0.43 and 0.73 for coronary death or incident non-fatal MI). A significant interaction was found between decision latitude and overtime work in predicting coronary death, incident non-fatal MI, or definite angina pectoris (P = 0.025). Based on Model E adjustments, the HR for overtime work of 3–4 h was 1.78 (95% CI 1.10–2.89, P = 0.020) in the low-decision latitude group (two lowest tertiles, n = 3415) and 1.26 (95% CI 0.77–2.04, P = 0.36) in the high-decision latitude group (highest tertile, n = 2599). However, this interaction was lost in the analysis confined to coronary deaths and incident non-fatal MIs only (P = 0.46).
Finally, we examined all-cause mortality as an outcome. In the model adjusted for age, sex, marital status, and occupational grade, employees working 1 h overtime had a HR of 1.11 (95% CI 0.75–1.63, P = 0.60), those working two extra hours a day had a HR of 1.27 (0.83–1.94, P = 0.27), and those working 3–4 h overtime a day had a HR of 1.35 (0.82–2.21, P = 0.24) when compared with employees not working overtime.