title: Night work and breast cancer in women: a Swedish cohort study.
abstract: OBJECTIVE
  Recent research has suggested a moderate link between night work and breast cancer in women, mainly through case-control studies, but non-significant studies are also common and cohort studies are few. The purpose of the present study was to provide new information from cohort data through investigating the association between the number of years with night work and breast cancer among women.
  
  
  METHODS
  Cohort study of individuals exposed to night shift work in relation to incidence of breast cancer in women.
  
  
  METHODS
  Individuals in the Swedish Twin registry, with follow-up in the Swedish Cancer Registry.
  
  
  METHODS
  13,656 women from the Swedish Twin Registry, with 3404 exposed to night work.
  
  
  METHODS
  Breast cancer from the Swedish Cancer Registry (463 cases) during a follow-up time of 12 years.
  
  
  RESULTS
  A Cox proportional hazards regression analysis with control for a large number of confounders showed that the HR was HR=1.68 (95% CI 0.98 to 2.88) for the group with >20 years of night work. When the follow-up time was limited to ages below 60 years, those exposed >20 years showed a HR=1.77 (95% CI 1.03 to 3.04). Shorter exposure to night work showed no significant effects.
  
  
  CONCLUSIONS
  The present results, together with previous work, suggest that night work is associated with an increased risk of breast cancer in women, but only after relatively long-term exposure.
authors: Department of Clinical Neuroscience, Karolinska Institutet, Stockholm, Sweden Stress Research Institute, Stockholm University, Stockholm, Sweden.
authors: Torbjörn
authors: T
authors: Åkerstedt
authors: Department of Health Sciences, Mid Sweden University, Sundsvall, Sweden.
authors: Anders
authors: A
authors: Knutsson
authors: Department of Clinical Neuroscience, Karolinska Institutet, Stockholm, Sweden.
authors: Jurgita
authors: J
authors: Narusyte
authors: Department of Clinical Neuroscience, Karolinska Institutet, Stockholm, Sweden.
authors: Pia
authors: P
authors: Svedberg
authors: Stress Research Institute, Stockholm University, Stockholm, Sweden Behavioral Science Institute, Radboud University, Nijmegen, The Netherlands.
authors: Göran
authors: G
authors: Kecklund
authors: Department of Clinical Neuroscience, Karolinska Institutet, Stockholm, Sweden.
authors: Kristina
authors: K
authors: Alexanderson
mesh_terms: D000328:Adult; D001943:Breast Neoplasms / Q000453:epidemiology / Q000209:etiology*; D016022:Case-Control Studies; D002940:Circadian Rhythm; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D015994:Incidence; D008875:Middle Aged; D016016:Proportional Hazards Models; D011446:Prospective Studies; D012042:Registries; D012307:Risk Factors; D013548:Sweden / Q000453:epidemiology; D014940:Work Schedule Tolerance
keywords: OCCUPATIONAL & INDUSTRIAL MEDICINE