title: Rotating night shift work and mammographic density.
abstract: BACKGROUND
  An increased risk of breast cancer has been observed in night shift workers. Exposure to artificial light at night and disruption of the endogenous circadian rhythm with suppression of the melatonin synthesis have been suggested mechanisms. We investigated the hypothesis that rotating night shift work is associated with mammographic density.
  
  
  METHODS
  We conducted a cross-sectional study on the association between rotating night shift work characteristics, 6-sulfatoxymelatonin (MT6s) creatinine adjusted in a spot morning urine sample, and a computer-assisted measure of mammographic density in 640 nurses and midwives ages 40 to 60 years. The associations were evaluated using regression models adjusted for age, body mass index, menopausal status, age at menopause, age at menarche, smoking, and the calendar season of the year when mammography was conducted.
  
  
  RESULTS
  The adjusted means of percentage of mammographic density and absolute density were slightly higher among women working rotating night shifts but not statistically significant [percentage of mammographic density = 23.6%, 95% confidence interval (CI), 21.9%-25.4% vs. 22.5%, 95% CI, 20.8%-24.3%; absolute density = 23.9 cm(2), 95% CI, 21.4-26.4 cm(2) vs. 21.8 cm(2), 95% CI, 19.4-24.3 cm(2) in rotating night shift and day shift nurses, respectively). There were no significant associations between the current or cumulative rotating night shift work exposure metrics and mammographic density. No association was observed between morning MT6s and mammographic density.
  
  
  CONCLUSIONS
  The hypothesis on the link between rotating night shift work, melatonin synthesis disruption, and mammographic density is not supported by the results of the present study.
  
  
  CONCLUSIONS
  It is unlikely that the development of breast cancer in nurses working rotating night shifts is mediated by an increase in mammographic density.
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: Wojciech
authors.initials: W
authors.lastname: Sobala
authors.forename: Edyta
authors.initials: E
authors.lastname: Reszka
authors.forename: Jolanta
authors.initials: J
authors.lastname: Gromadzinska
authors.forename: Wojciech
authors.initials: W
authors.lastname: Wasowicz
authors.forename: Jenny Anne
authors.initials: JA
authors.lastname: Lie
authors.forename: Helge
authors.initials: H
authors.lastname: Kjuus
authors.forename: Giske
authors.initials: G
authors.lastname: Ursin
mesh_terms: D000328:Adult; D001940:Breast / Q000473:pathology*; D001943:Breast Neoplasms / Q000209:etiology* / Q000473:pathology*; D002940:Circadian Rhythm / Q000502:physiology*; D003430:Cross-Sectional Studies; D005260:Female; D006801:Humans; D008550:Melatonin / Q000652:urine; D008875:Middle Aged; D008880:Midwifery; D009740:Nursing Staff; D012307:Risk Factors; D011795:Surveys and Questionnaires; D014940:Work Schedule Tolerance
chemical_list: D008550:Melatonin