Environment and Breast Cancer: Science Review

Evidence From Humans
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Physical activity and breast cancer risk: the Women's Health Study (United States)
Lee, I. M.,, Rexrode, K. M.,, Cook, N. R.,, Hennekens, C. H.,, Buring, J. E. Cancer Causes and Control. 2001. 12, 137-145.
Topic area
Physical Activity
Study design
Prospective cohort
Funding agency
NCI Other: National Heart, Lung, and Blood Institu
Study Participants
Number of Cases
411 (322 invasive and 79 in-situ) (143 pre) (261 post)
Menopausal Status
The menopausal status of women included in this study is listed here.
Pre menopausal
Post menopausal
Number in Cohort
Cohort: 39,322
Cohort participation rate
Retention/participation exceeded 70% for exposed a
Participant selection: Inclusion and exclusion criteria
Criteria used to select participants in the study.
In: women, mostly nurses, > 45 years of age who participated in the Women's Health study between 9/92 and 5/95; resident of the United States of Puerto Rico; completed a mailed baseline questionnaire; women reported being free of coronary heart disease, cerebrovascular disease and cancer Ex: women who did not provide any information on physical activity or weight at study entry; women whose cases were not confirmed after medical review
Comment about participation selection
Strengths: prospective study; all cases were confirmed through medical record review; assessed breast cancer risk by physical activity stratified by menopausal status and by women who had positive estrogen and progesterone hormone receptors; one of the first and only studies to examine the association between physical activity and breast cancers that were positive for steroid receptors Limitations: self-reported variables; had data on hormone receptors for only 71% of breast cancers; did not measure physical activity at different stages of life
Exposure Investigated
Exposures investigated
Physical inactivity
How exposure was measured
Questionnaire, self-administered
Exposure assessment comment
Self-reported variables
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 more than 6 months, number of pregnancies lasting more than 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: 4 years
Strength of associations reported
No association between breast cancer risk and physical activity, >6300 kJ/week of energy expenditure vs. <840 kJ/week, RR=0.80(0.58-1.12)
Association between breast cancer risk and postmenopausal physical activity, >6300 kJ/week of energy expenditure vs. <840 kJ/week, RR=0.67(0.44-1.02) trend p=0.03