title: Estimation of the benchmark duration of alternating shift work associated with increased total cholesterol levels among male Japanese workers.
abstract: OBJECTIVE
  The aim of this study was to estimate the benchmark doses (BMD) and their 95% lower confidence limits (BMDL) for the threshold number of years of alternating shift work associated with a relative increase in serum total cholesterol level (T-Cho), as an index of lipid metabolism.
  
  
  METHODS
  We conducted a 14-year prospective cohort study among male workers (N=6886) at a Japanese steel company who had received annual health check-ups between 1991 and 2005. The endpoints were either a 20, 25, 30, 35, 40 or 45% increase in T-Cho levels during the observation period, compared to T-Cho at baseline. We investigated the associations between the years of alternating shift work and the relative increases in T-Cho using pooled logistic regression, adjusted for other potential covariates.
  
  
  RESULTS
  We estimated the BMDL and BMD for years of alternating shift work among 40-, 50-, or >50-year old subjects using benchmark responses (BMR) of 5 or 10% and parameters for the duration of alternating shift work and other covariates. Assuming a mean age of 44 years among workers in their 40s, the BMDL/BMD for years of alternating shift work with a BMR of 5% were 21.0/28.0 (> or =20%), 21.3/26.1 (> or =25%), 24.1/28.8 (> or =30%), 25.6/29.8 (> or =35%), 27.1/31.5 (> or =40%), and 27.7/32.1 (> or =45%).
  
  
  CONCLUSIONS
  The threshold number of years of alternating shift work that caused a 5% increase in T-Cho was shown to be > or =21 years among middle-aged workers. Special attention should be paid to influence the process at an earlier stage and not when the risk has already materialized.
authors.affiliation: Department of Occupational and Environmental Medicine, Graduate School of Medicine, Chiba University, Chuoku, Chiba, 260-8670, Japan. suwa@faculty.chiba-u.jp
authors.forename: Yasushi
authors.initials: Y
authors.lastname: Suwazono
authors.forename: Mirei
authors.initials: M
authors.lastname: Uetani
authors.forename: Mitsuhiro
authors.initials: M
authors.lastname: Oishi
authors.forename: Kumihiko
authors.initials: K
authors.lastname: Tanaka
authors.forename: Hideki
authors.initials: H
authors.lastname: Morimoto
authors.forename: Satoru
authors.initials: S
authors.lastname: Nakada
authors.forename: Kouichi
authors.initials: K
authors.lastname: Sakata
mesh_terms: D000328:Adult; D019985:Benchmarking; D002784:Cholesterol / Q000097:blood*; D015331:Cohort Studies; D006801:Humans; D007564:Japan; D008297:Male; D008875:Middle Aged; D011446:Prospective Studies; D014940:Work Schedule Tolerance / Q000502:physiology*; D055815:Young Adult
chemical_list: D002784:Cholesterol