title: Night shift work characteristics and 6-sulfatoxymelatonin (MT6s) in rotating night shift nurses and midwives.
abstract: OBJECTIVE
  Synthesis of melatonin follows a circadian cycle, with high melatonin levels during the night and low levels during the day. Light exposure at night has been hypothesised as one of potential mechanisms of breast carcinogenesis in the night shift workers through inhibition of melatonin synthesis. The aim of the study was to examine a number of determinants for night shift work in relation to 6-sulfatoxymelatonin (MT6s), primary melatonin metabolite.
  
  
  METHODS
  The cross-sectional study included 354 nurses and midwives (aged 40-60 years) currently working on rotating night shifts and 370 working days only. Data from questionnaires and 1-week diaries were used to characterise current job and total occupational history. Associations between rotating night shift work characteristics and MT6s (creatinine adjusted) in spot morning urine were tested in multiple linear regression models.
  
  
  RESULTS
  No significant differences were found for MT6s concentrations between women currently working on rotating night shifts and those working only day shifts (means 47.2 vs 45.7 ng/mg Cr, respectively). The adjusted means among rotating night shift nurses and midwives varied depending on the department of employment, from 35.1 ng/mg Cr in neonatology to 68.2 ng/mg Cr in the orthopaedics department. Women working eight or more night shifts per month had significantly lower MT6s levels than those having fewer night shifts per month (37.9 vs 47.4 ng/mg Cr, respectively). Total night shift work history was not associated with MT6s.
  
  
  CONCLUSIONS
  The results of this study indicate that working eight or more night shifts per month may disrupt the synthesis of melatonin.
authors.affiliation: Department of Environmental Epidemiology, Nofer Institute of Occupational Medicine, Lodz, Poland. beatap@imp.lodz.pl
authors.forename: Beata
authors.initials: B
authors.lastname: Peplonska
authors.forename: Agnieszka
authors.initials: A
authors.lastname: Bukowska
authors.forename: Jolanta
authors.initials: J
authors.lastname: Gromadzinska
authors.forename: Wojciech
authors.initials: W
authors.lastname: Sobala
authors.forename: Edyta
authors.initials: E
authors.lastname: Reszka
authors.forename: Jenny-Anne
authors.initials: JA
authors.lastname: Lie
authors.forename: Helge
authors.initials: H
authors.lastname: Kjuus
authors.forename: Wojciech
authors.initials: W
authors.lastname: Wasowicz
mesh_terms: D000328:Adult; D002940:Circadian Rhythm / Q000502:physiology*; D003430:Cross-Sectional Studies; D005260:Female; D006801:Humans; D008297:Male; D008550:Melatonin / Q000031:analogs & derivatives* / Q000652:urine; D008875:Middle Aged; D008880:Midwifery; D009740:Nursing Staff; D012890:Sleep / Q000502:physiology*; D011795:Surveys and Questionnaires; D014940:Work Schedule Tolerance / Q000502:physiology*
chemical_list: C054513:6-sulfatoxymelatonin; D008550:Melatonin