title: Self reported stress and risk of breast cancer: prospective cohort study.
abstract: OBJECTIVE
  To assess the relation between self reported intensity and frequency of stress and first time incidence of primary breast cancer.
  
  
  METHODS
  Prospective cohort study with 18 years of follow-up.
  
  
  METHODS
  Copenhagen City heart study, Denmark.
  
  
  METHODS
  The 6689 women participating in the Copenhagen City heart study were asked about their perceived level of stress at baseline in 1981-3. These women were followed until 1999 in the Danish nationwide cancer registry, with < 0.1% loss to follow-up.
  
  
  METHODS
  First time incidence of primary breast cancer.
  
  
  RESULTS
  During follow-up 251 women were diagnosed with breast cancer. After adjustment for confounders, women with high levels of stress had a hazard ratio of 0.60 (95% confidence interval 0.37 to 0.97) for breast cancer compared with women with low levels of stress. Furthermore, for each increase in stress level on a six point stress scale an 8% lower risk of primary breast cancer was found (hazard ratio 0.92, 0.85 to 0.99). This association seemed to be stable over time and was particularly pronounced in women receiving hormone therapy.
  
  
  CONCLUSIONS
  High endogenous concentrations of oestrogen are a known risk factor for breast cancer, and impairment of oestrogen synthesis induced by chronic stress may explain a lower incidence of breast cancer in women with high stress. Impairment of normal body function should not, however, be considered a healthy response, and the cumulative health consequences of stress may be disadvantageous.
authors.affiliation: National Institute of Public Health, Øster Farimagsgade 5A, DK-1399 Copenhagen K, Denmark. nrn@niph.dk
authors.forename: Naja Rod
authors.initials: NR
authors.lastname: Nielsen
authors.forename: Zuo-Feng
authors.initials: ZF
authors.lastname: Zhang
authors.forename: Tage S
authors.initials: TS
authors.lastname: Kristensen
authors.forename: Bo
authors.initials: B
authors.lastname: Netterstrøm
authors.forename: Peter
authors.initials: P
authors.lastname: Schnohr
authors.forename: Morten
authors.initials: M
authors.lastname: Grønbaek
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001943:Breast Neoplasms / Q000453:epidemiology / Q000523:psychology*; D003718:Denmark / Q000453:epidemiology; D004812:Epidemiologic Methods; D005260:Female; D006801:Humans; D008875:Middle Aged; D013315:Stress, Psychological / Q000150:complications* / Q000453:epidemiology