title: Overtime work and blood pressure in normotensive Japanese male workers.
abstract: BACKGROUND
  Epidemiological studies have observed conflicting patterns as to whether overtime work increases blood pressure (BP), probably as a consequence of methodological issues.
  
  
  METHODS
  We conducted a prospective cohort study to investigate the relationship between overtime work hours and 1-year changes in BP in 1,235 normotensive Japanese male workers who carried out a variety of jobs in a manufacturing factory. Casual BP measurements were repeated at annual health examinations in 2004-2005, using an automatic manometer. An analysis of covariance that incorporated potential confounding factors including baseline age, body mass index (BMI), and lifestyle factors was used to calculate and compare the means of the 1-year change in systolic (SBP) and diastolic BP (DBP). The participants were grouped according to their average monthly overtime work hours obtained from timecard data between April and September 2004.
  
  
  RESULTS
  The multivariate-adjusted mean for 1-year change in DBP in 611 male assembly-line workers was 1.5 mm Hg (95% confidence interval (CI) 0.8-2.2) for <40.0 h/month, 2.3 mm Hg (95% CI 1.3-3.2) for 40.0-79.9 h/month, and 5.3 mm Hg (95% CI 2.7-7.9) for ≥ 80.0 h/month (P for heterogeneity = 0.02). A broadly similar pattern was observed for SBP. In contrast, there was no significant difference in means 1-year change for both SBP and DBP in 315 clerks and 309 engineers/special technicians, grouped according to overtime work hours.
  
  
  CONCLUSIONS
  Extensive overtime work was associated with increased BP in normotensive male assembly-line workers, but not in clerks and engineers/special technicians.
authors.affiliation: Department of Epidemiology and Public Health, Kanazawa Medical University, Uchinada, Japan. knaka@kanazawa-med.ac.jp
authors.forename: Koshi
authors.initials: K
authors.lastname: Nakamura
authors.forename: Masaru
authors.initials: M
authors.lastname: Sakurai
authors.forename: Yuko
authors.initials: Y
authors.lastname: Morikawa
authors.forename: Katsuyuki
authors.initials: K
authors.lastname: Miura
authors.forename: Masao
authors.initials: M
authors.lastname: Ishizaki
authors.forename: Teruhiko
authors.initials: T
authors.lastname: Kido
authors.forename: Yuchi
authors.initials: Y
authors.lastname: Naruse
authors.forename: Yasushi
authors.initials: Y
authors.lastname: Suwazono
authors.forename: Hideaki
authors.initials: H
authors.lastname: Nakagawa
mesh_terms: D000328:Adult; D044466:Asian People; D001794:Blood Pressure / Q000502:physiology*; D015331:Cohort Studies; D005500:Follow-Up Studies; D006801:Humans; D006973:Hypertension / Q000453:epidemiology* / Q000503:physiopathology; D007564:Japan / Q000453:epidemiology; D008297:Male; D008875:Middle Aged; D011446:Prospective Studies; D014940:Work Schedule Tolerance / Q000502:physiology*