Physical activity and the risk of breast cancer

N Engl J Med. 1997 May 1;336(18):1269-75. doi: 10.1056/NEJM199705013361801.


Background: Because physical activity may affect hormonal concentrations and energy balance, we decided to investigate whether everyday exercise is related to the risk of breast cancer.

Methods: During 1974 to 1978 and 1977 to 1983, a total of 25,624 women, 20 to 54 years of age at entry, enrolled in health surveys and answered questionnaires about leisure-time and work activity.

Results: During a median follow-up of 13.7 years, we identified 351 cases of invasive breast cancer among the 25,624 women in the cohort. Greater leisure-time activity was associated with a reduced risk of breast cancer, after adjustments for age, body-mass index (the weight in kilograms divided by the square of the height in meters), height, parity, and county of residence (relative risk, 0.63; 95 percent confidence interval, 0.42 to 0.95), among women who exercised regularly, as compared with sedentary women (P for trend=0.04). In regularly exercising women, the reduction in risk was greater in premenopausal women than in postmenopausal women, and greater in younger women (<45 years at study entry) than in older women (> or =45 years) (relative risk, 0.38; 95 percent confidence interval, 0.19 to 0.79). In stratified analyses the risk of breast cancer was lowest in lean women (body-mass index, <22.8) who exercised at least four hours per week (relative risk, 0.28; 95 percent confidence interval, 0.11 to 0.70). The risk was also reduced with higher levels of activity at work, and again there was a more pronounced effect among premenopausal than postmenopausal women.

Conclusions: Physical activity during leisure time and at work is associated with a reduced risk of breast cancer.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adult
  • Age Factors
  • Aged
  • Body Weight
  • Breast Neoplasms / epidemiology*
  • Breast Neoplasms / prevention & control
  • Exercise*
  • Female
  • Follow-Up Studies
  • Health Surveys
  • Humans
  • Incidence
  • Leisure Activities
  • Middle Aged
  • Norway / epidemiology
  • Proportional Hazards Models
  • Risk
  • Risk Factors
  • Work