title: Multicenter historical cohort study of the relationship between shift work and blood pressure.
abstract: BACKGROUND
  Regarding the relationship between blood pressure (BP) and shift work (SW), previous studies have reported contradictory results. In the present study, we used Bayesian multilevel modeling to evaluate the association of SW and BP after controlling some confounding factors.
  
  
  METHODS
  Data of this multicenter historical study were extracted from annual observations of the male workers of Isfahan's Mobarakeh Steel Company (IMSC) and Polyacryl Iran Corporation (PIC) in Isfahan, Iran, between 2003 and 2011. In this research, we assessed the effect of SW on systolic BP (SBP) and diastolic BP (DPB) with controlling body mass index, age, work experience, marriage, and education status.
  
  
  RESULTS
  A total of 8613 (IMSC, n = 5314 and PIC, n = 3299) workers participated in this study with a mean [standard deviation (SD)] age of 41.60 (8.30) and mean (SD) work experience of 16.17 (7.89) years. In this study, after controlling confounding factors, we found no significant relationship between SW and SBP and DBP.
  
  
  CONCLUSIONS
  In general, the results of this multicenter cohort study did not support a relationship between SW and BP. We suggest prospective studies with controlling more confounding factors in this area.
authors: Assistant Professor, Department of Biostatistics, School of Medical Sciences, Tarbiat Modares University, Tehran, Iran.
authors: Mohammad
authors: M
authors: Gholami-Fesharaki
authors: Professor, Department of Biostatistics, School of Medical Sciences, Tarbiat Modares University, Tehran, Iran.
authors: Anoshirvan
authors: A
authors: Kazemnejad
authors: Associate Professor, Proteomics Research Center, School of Paramedical Sciences, Shahid Beheshti University of Medical Sciences, Tehran, Iran.
authors: Farid
authors: F
authors: Zayeri
authors: General Practitioner, Worksite Follow-Up Unit, Occupational Health Center, Mobarakeh Steel Company, Isfahan, Iran.
authors: Mohsen
authors: M
authors: Rowzati
authors: General Practitioner, Occupational Health Center, Polyacryle Company, Isfahan, Iran.
authors: Javad
authors: J
authors: Sanati
authors: Health Research Center, Baqiyatallah University of Medical Sciences, Tehran, Iran.
authors: Hamed
authors: H
authors: Akbari
keywords: Bayesian Method; Blood Pressure; Iran; Multilevel Analyses