title: Retrospective cohort study of the risk of impaired glucose tolerance among shift workers.
abstract: OBJECTIVE
  The aim of this study was to investigate the effect of shift working on the risk of developing impaired glucose tolerance (IGT).
  
  
  METHODS
  This study comprised 6413 male employees (5608 daytime workers, 512 3-shift workers and 293 2-shift workers) whose work schedules remained constant during the follow-up period (mean follow-up period 9.9 years). IGT was defined as Hemoglobin A1c ≥ 5.9%. The Cox proportional hazards model was used to estimate the risk of developing IGT, after making adjustments for age, smoking, alcohol consumption, leisure-time physical activity, body mass index (BMI) and Hemoglobin A1c (HbA1c) at baseline. Analysis was additionally performed for a sub-cohort of 1625 workers with BMI of 20.0-25.0 kg/m² that did not change by >2.0 kg/m² during the follow up period.
  
  
  RESULTS
  The risk of developing IGT was significantly elevated among both 3-shift workers [hazard ratio (HR) 1.78, 95% confidence interval (95% CI) 1.49- 2.14] and 2-shift workers (HR 2.62, 95% CI 2.17-3.17). Significant elevations of the risk were still observed at the additional analysis on the sub-cohort (3-shift work: HR 3.55, 95% CI 2.02-6.25; 2-shift work: HR 4.86, 95% CI 2.62-9.01).
  
  
  CONCLUSIONS
  Both 2- and 3-shift workers were associated with a high risk factor of developing IGT compared to day workers. Moreover, 2-shift workers had a higher risk than 3-shift workers. The risk was observed even among workers whose body mass remained within the normal range.
authors.affiliation: Corporate Environmental Safety Health and Quality Assurance, Asahi Kasei Corporation, Tokyo, Japan.
authors.forename: Ichiro
authors.initials: I
authors.lastname: Oyama
authors.forename: Tatsuhiko
authors.initials: T
authors.lastname: Kubo
authors.forename: Yoshihisa
authors.initials: Y
authors.lastname: Fujino
authors.forename: Koji
authors.initials: K
authors.lastname: Kadowaki
authors.forename: Masamizu
authors.initials: M
authors.lastname: Kunimoto
authors.forename: Kiyoyumi
authors.initials: K
authors.lastname: Shirane
authors.forename: Hidetoshi
authors.initials: H
authors.lastname: Tabata
authors.forename: Ken
authors.initials: K
authors.lastname: Sabanai
authors.forename: Takehiro
authors.initials: T
authors.lastname: Nakamura
authors.forename: Shinya
authors.initials: S
authors.lastname: Matsuda
mesh_terms: D015992:Body Mass Index; D005951:Glucose Tolerance Test; D006442:Glycated Hemoglobin / Q000032:analysis; D006801:Humans; D008297:Male; D016016:Proportional Hazards Models; D012189:Retrospective Studies; D014940:Work Schedule Tolerance
chemical_list: D006442:Glycated Hemoglobin; C517652:hemoglobin A1c protein, human