Environment and Breast Cancer: Science Review

Evidence From Humans
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Lifetime physical activity and risk of breast cancer
Lee, I.M., , Cook, N.R., , Rexrode, K.M., , Buring, J.E. British Journal of Cancer. 2001. 85:7, 962-965.
Topic area
Physical Activity
Study design
Nested case-control
Funding agency
Study Participants
Number of Cases
364 (131 pre) (233 post)
Menopausal Status
The menopausal status of women included in this study is listed here.
Pre menopausal
Post menopausal
Number of Controls
Controls: 715 (253 pre) (462 post)
Participant selection: Inclusion and exclusion criteria
Criteria used to select participants in the study.
In: participants of the Women's Health Study who developed breast cancer (cases); participants of the Women's Health Study who were age matched to cases (controls) Ex: women who died of breast cancer before the initiation of the study (10/99)
Comment about participation selection
Strengths: High participation rate; confirmed cases with medical records; assessed breast cancer risk and physical activity at four different age periods; one of the few studies to integrate assessments of physical activity at different ages in women's lives to examine lifetime physical activity; cases and controls had similar levels of physical activity and weights; used MET hours per week (1 MET-hour= energy expended while sitting quietly for one hour) to obtain physical activity levels Limitations: conducted a nested case-control; physical activity levels were self-reported; did not note the MET values for each quartile at each age period; relatively few cases
Exposure Investigated
Exposures investigated
Sedentary lifestyle
How exposure was measured
Questionnaire, self-administered
Exposure assessment comment
Physical activity levels were self-reported
Early life exposures considered
Physical activity age 12-18
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: BMI, alcohol consumption, age at menarche, age at first pregnancy lasting > 6months, number of pregnancies lasting > 6 months, menopausal status, oc use, HRT use, family history of breast cancer
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
Follow-up: 48 months average
Strength of associations reported
No association between breast cancer risk and lifetime physical activity, Q4 vs. Q1, OR=1.10(0.73-1.67) trend p=0.47
Results Comments
No association between breast cancer risk and physical activity during any of the 4 age periods analyzed
Controls participation rate
Greater than 70% (91%)