Objectives The authors investigated the effect of shift working on the risk of obesity using data from the Industry-based Shift Workers' Health (IbSH) study, a retrospective cohort study based on a health care database system belonging to a manufacturing corporation in Japan.
Methods The study database contains data on annual health check-ups and work schedules for every worker in the corporation in Japan since 1981. Study subjects consisted of 9912 male employees (8892 daytime workers and 920 rotating three-shift workers; mean age at first check-up was 23.7 years) whose work schedules were consistent during the follow-up period. Obesity was defined as a body mass index ≥25.0.
Results 3319 cases of obesity were recorded over the 27.5 years of retrospective follow-up. Kaplan–Meier survival analysis visually demonstrated an increased risk of obesity among shift workers. The risk becomes particularly obvious after 10 years of follow-up. Cox proportional-hazards model analysis revealed a significantly increased risk among shift workers (RR 1.14, 95% CI 1.01 to 1.28).
Conclusion The risk of obesity among male shift workers was visually and statistically demonstrated.
- Work schedule tolerance
- shift work
- historical cohort study
- occupational health practice
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Funding This work was supported by KAKENHI, a Grant-in-Aid for Young Scientists (B) (No 19790437) and Scientific Research (C) (No 22590618) from the Ministry of Education, Culture, Sports, Science and Technology, Japan.
Competing interests None.
Ethics approval This study was conducted with the approval of the Ethics Committee for Medical Care and Research at The University of Occupational and Environmental Health, Japan.
Provenance and peer review Not commissioned; externally peer reviewed.