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Public health
Research
Long weekly working hours and ischaemic heart disease: a follow-up study among 145 861 randomly selected workers in Denmark
  1. Harald Hannerz1,
  2. Ann Dyreborg Larsen1,
  3. Anne Helene Garde1,2
  1. 1 National Research Centre for the Working Environment, Copenhagen, Denmark
  2. 2 Department of Public Health, University of Copenhagen, Copenhagen, Denmark
  1. Correspondence to Harald Hannerz; hha{at}nrcwe.dk

Abstract

Objectives The 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 participants Data 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.

Results In 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.

Conclusion In this Danish sample, we did not find any statistically significant association between WWH and IHD or antihypertensive drug usage.

  • EU working time directive
  • hypothesis testing
  • blinded statistical analysis
  • occupational health
  • hospital treatment
  • cardiovascular disease

This is an open access article distributed in accordance with the Creative Commons Attribution Non Commercial (CC BY-NC 4.0) license, which permits others to distribute, remix, adapt, build upon this work non-commercially, and license their derivative works on different terms, provided the original work is properly cited and the use is non-commercial. See: http://creativecommons.org/licenses/by-nc/4.0/

https://doi.org/10.1136/bmjopen-2017-019807

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    Footnotes

    • Contributors The statistical analysis was conducted by HH. The manuscript was written by HH, ADL and AHG.

    • Funding The project was funded by the Danish taxpayers, through the Danish Work Environment Research Foundation, grant number 20130069288.

    • Competing interests None declared.

    • Patient consent Not required.

    • Ethics approval The study [complies] with The Act on Processing of Personal Data, Denmark (Act No. 429 of 31 May 2000), which implements the European Union (EU) Directive 95/46/EC on the protection of individuals. The data usage is approved by the Danish Data Protection Agency, file number 2001-54-0180. The ethical aspect of the project was examined and approved by Statistics Denmark, account number 704291.14

    • Provenance and peer review Not commissioned; externally peer reviewed.

    • Data sharing statement The authors do not own the data of the study. The data belong to Statistics Denmark and may only be used with their permission.