Long weekly working hours and ischaemic heart disease: a follow-up study among 145 861 randomly selected workers in Denmark

Abstract

ObjectivesThe aim of the present study was to test if incidences of ischaemic heart disease (IHD) and usage of antihypertensive drugs are independent of weekly working hours (WWH) among full-time employees in Denmark.Design and participantsData on WWH from participants of the Danish labour force surveys, 1999–2013, were linked on an individual level to national registers with data on socioeconomic status (SES), industry, emigrations, redeemed prescriptions, hospital contacts and deaths. Participants were followed until the end of 2014 (on average 7.7 years). Poisson regression was used to model incidence rates as a function of WWH. The analyses were controlled for calendar time, time passed since start of follow-up, employment in the healthcare industry, age, sex, SES and night work.ResultsIn total, we found 3635 cases of IHD and 20 648 cases of antihypertensive drug usage. The rate ratio of IHD was 0.95 (95% CI 0.85 to 1.06) for 41–48 compared with 32–40 WWH and 1.07 (0.94 to 1.21) for >48 compared with 32–40 WWH. The corresponding rate ratios for antihypertensive drug usage were 0.99 (0.95 to 1.04) and 1.02 (0.97 to 1.08). No statistically significant interactions between WWH and sex, SES and night work, respectively, were found.ConclusionIn this Danish sample, we did not find any statistically significant association between WWH and IHD or antihypertensive drug usage.

Long Working Hours and Risk of Cardiovascular Disease

“…Since the IPD-Work meta-analysis was published, at least two independent large-scale studies have examined the association between long working hours and cardiovascular disease. In these studies, responses of 145,861 to 199,035 employees to the Danish Labour Force Survey in 1999 to 2013 were linked to records of hospitalizations and deaths from national registers until 2014 [ 19 •, 20 •]. With 35–40 working hours per week as reference, the estimated rate ratio for working ≥ 55 h per week was 0.89 (95% CI 0.69–1.16) for overall stroke, 0.86 (95% CI 0.61–1.22) for ischemic stroke, and 1.33 (95% CI 0.82–2.15) for hemorrhagic stroke [ 19 •].…”

“…With 35–40 working hours per week as reference, the estimated rate ratio for working ≥ 55 h per week was 0.89 (95% CI 0.69–1.16) for overall stroke, 0.86 (95% CI 0.61–1.22) for ischemic stroke, and 1.33 (95% CI 0.82–2.15) for hemorrhagic stroke [ 19 •]. The rate ratio of ischemic heart disease for > 48 compared with 32–40 weekly working hours was 1.09 (95% CI 0.96–1.24 among participants without a recorded heart disease 5 years before the survey (the rate ratio was not reported for ≥ 55 weekly working hours) [ 20 •].…”

“…Figure 1 shows the current state of evidence on the association between long working hours and the onset of CHD and stroke, in which the results from the previous systematic review and individual-participant data meta-analysis by IPD-Work published in 2015, which included 22 studies on CHD and 14 studies on stroke [ 18 ••], are supplemented with findings from the Danish Labour Force Survey [ 19 •, 20 •], which were identified in our literature search of PubMed in June 30, 2018. The Danish studies are based on the same population-based cohort from Denmark, with an average follow-up of 7.7 years.…”

“…The Danish studies are based on the same population-based cohort from Denmark, with an average follow-up of 7.7 years. For the CHD meta-analysis, we used the estimate in which all CHD cases 5 years before the survey were excluded instead of 1 year, as was done in the main analysis of that study [ 20 •]. We used random effects meta-analysis (Stata 15.1) to obtain new relative risk estimates for CHD and stroke, including all original estmates from 22 CHD studies and 14 stroke studies in the analyses, to which we added the estimates reported in the Danish studies.…”

Sociomedical problems of overwork-related deaths and disorders in Japan

“…Recent findings for prospective studies with large sample sizes support the hypothesis that stroke is more closely related to long working hours. 7,9,17 Regarding the occupational risk factors, chronic exposure to long working hours played a principal role. On average, the monthly overtime during the past 6 months before the disease onset was found to increase from 86, 89, 91, 93, 95, and 100 hours in the past 6, 5, 4, 3, 2, and 1 months, respectively.…”