Intended for healthcare professionals


Self reported stress and risk of breast cancer: prospective cohort study

BMJ 2005; 331 doi: (Published 08 September 2005) Cite this as: BMJ 2005;331:548
  1. Naja Rod Nielsen, student and research assistant (nrn{at},
  2. Zuo-Feng Zhang, professor2,
  3. Tage S Kristensen, professor3,
  4. Bo Netterstr⊘m, research director4,
  5. Peter Schnohr, consultant5,
  6. Morten Gr⊘nbæk, professor2
  1. 1 National Institute of Public Health, Øster Farimagsgade 5A, DK-1399 Copenhagen K, Denmark
  2. 2 Department of Epidemiology, UCLA School of Public Health, Los Angeles, CA, USA
  3. 3 National Institute of Occupational Health, Copenhagen
  4. 4 Clinic of Occupational Medicine, Hiller⊘d Hospital, Hiller⊘d, Denmark
  5. 5 Copenhagen City Heart Study, Epidemiological Research Unit, Bispebjerg University Hospital, Copenhagen
  1. Correspondence to: N R Nielsen
  • Accepted 27 June 2005


Objective To assess the relation between self reported intensity and frequency of stress and first time incidence of primary breast cancer.

Design Prospective cohort study with 18 years of follow-up.

Setting Copenhagen City heart study, Denmark.

Participants 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.

Main outcome measure 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.

Conclusion 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.


  • Contributors NRN contributed to the conception and design of the study, the analysis and interpretation of data, and the drafting the paper. Z-FZ, TSK, BN, and MG contributed to the conception and design of the study and to critically revising the paper. PS contributed to the design of the study, the acquisition of data, and critically revising the paper. TSK designed the stress questions used in the study. All authors approved the final version of the article. MG is the guarantor.

  • Competing interests None declared.

  • Funding This study was supported by funds from the Health Insurance Foundation.

  • Ethical approval The Danish ethics committee for the City of Copenhagen and Frederiksberg approved the study (#100.2039/91).

  • Accepted 27 June 2005
View Full Text