Environment and Breast Cancer: Science Review

Evidence From Humans
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Case-control study of lifetime physical activity and breast cancer risk
C.M. Friedenreich, H.E. Bryant, K.S. Courneya American Journal of Epidemiology. 2001. 154, 336-347.
Topic area
Physical Activity
Study design
Population based case-control
Funding agency
Other: Canadian Breast Cancer Research Initiative
Study Participants
Number of Cases
1,233 (463 pre) (770 post) (in situ and invasive only)
Menopausal Status
The menopausal status of women included in this study is listed here.
Pre menopausal
Post menopausal
Number of Controls
Controls: 1,237 (475 pre) (762 post)
Participant selection: Inclusion and exclusion criteria
Criteria used to select participants in the study.
In: women diagnosed with in situ and invasive breast cancer in Alberta, Canada between 8/95 and 8/97 (cases); resident of Alberta; younger than 80 years old; English speaking; completed interview; had a listed telephone number (controls) Ex: could not speak English; changed telephone numbers or had a disconnected telephone during the study; had incomplete interviews; diagnosed with a prior cancer; had many missing values
Comment about participation selection
Strengths: large population based case control study; cases were histologically confirmed; conducted in-person interviews; assessed diet; anthropometric data was measured by trained staff; assessed occupational, household and recreational activity using MET (ratio of the associated metabolic rate for a specific activity compared to the resting metabolic rate); compared controls to a sample of Albertans to address the issue of selection bias due to a low participation rate from controls; analyzed breast cancer risk by different types of physical activity stratified by menopausal status; one of the first studies to report effect modification on physical activity with breast cancer risk by alcohol consumption and smoking status Limitations: possible selection bias due to a low participation rate amongst controls; possible misclassification of exposure due to self-reported lifetime physical activity patterns
Exposures investigated
Sedentary lifestyle
How exposure was measured
Questionnaire, in person
Statistical Analysis
Ethnic groups with separate analysis
If this study provided a separate analysis by ethnic or racial group, the groups are listed here.
Confounders considered
Other breast cancer risk factors, such as family history, age at first birth, and hormone replacement therapy use, that were taken into account in the study.
Adequately controlled, confounders: age, WHR, education, HRT use, history of benign breast disease, family history of breast cancer, alcohol consumption, smoking status
Genetic characterization included
If the study analyzed relationships between environmental factors and inherited genetic variations, this field will be marked “Yes.” “No”, if not.
Description of major analysis
Effect modification: menopausal status, alcohol consumption; smoking status, parity and BMI
Strength of associations reported
Inverse association between postmenopausal breast cancer risk and a high level of lifetime occupational physical activity, OR=0.59(0.44-0.81)
Inverse association between postmenopausal breast cancer risk and a high level of lifetime household physical activity, OR=0.57(0.41-0.79)
Results Comments
Effect modification by alcohol consumption, smoking status and parity
Controls participation rate
Less than 70% (56.5%)