This summary table contains detailed information about research studies. Summary tables offer an informative look at the science behind many breast cancer guidelines and recommendations. However, they should be viewed with some caution. In order to read and interpret research tables successfully, it is important to understand some key concepts. Learn how to read a research table.
Introduction: Exercise (physical activity) may lower the risk of breast cancer. Although not all studies show this benefit, when the evidence is looked at as a whole, regular exercise seems to moderately lower risk. This is seen most clearly in postmenopausal women .
Learn more about exercise and breast cancer risk.
Learn about the strengths and weaknesses of different types of studies. See how this risk factor compares with other risk factors for breast cancer.
* Please note, the information provided within Komen Perspectives articles is only current as of the date of posting. Therefore, some information may be out of date at this time.
Study selection criteria: Prospective cohort studieswith at least 800 breast cancer cases and meta-analyses. Table notes: Relative risk above 1 indicates increased risk. Relative risk below 1 indicates decreased risk. MET (metabolic equivalent) hours are often used as a measure of physical activity. One MET hour equals the energy used to sit quietly for one hour. Different activities have different MET scores. Moderate activities, like mowing the lawn or slow dancing, range from 3 to 6 MET hours. Vigorous activities, like playing tennis or jogging, score higher than 6 MET hours. For example, walking is 3 MET hours and swimming is 7 MET hours.
(number of participants)
Levels of Activity Compared
Relative Risk of Breast Cancer in Physically Active Women Compared to Inactive Women, RR (95% CI)
Pre- and post-menopausal combined
Prospective cohort studies
More than 42
14 or fewer MET hr/wk recreational activity
NIH-AARP Diet and Health Study [3,4]
At least 20 min activity at least 5 times/wk
Nurses' Health Study 
27 or more
less than 3 MET hr/wk
Cancer Prevention Study II-Nutrition Cohort 
More than 42 vs.
7 or fewer MET hr/wk
7 or more
3 or fewer hr/wk walking
French E3N cohort [7-8]
90,509 (3,424 cases)
22-34 MET hr/wk recreational activity
34 or more MET hr/wk recreational activity
California Teachers Study 
110,599 (2,649 cases)
5 or more hr/wk moderate physical activity
Women’s Health Initiative 
17 or more hr/wk vs. no activity
Iowa Women’s Health Study 
36,363 (2,548 cases)
High level of activity
National Breast Cancer Screening Study-Canada 
40,318 (2,545 cases)
At least 1 hr/day vigorous physical activity
Norwegian-Swedish Women’s Lifestyle and Health Cohort Study 
99,504 (1,166 cases)
Breast Cancer Detection Demonstration Project Follow-up Study 
32,269 (1,506 cases)
lower level of activity
Netherlands Cohort Study 
More than 90 minutes/day of activity
less than 30 minutes/day
U.S. Radiologic Technologies cohort 
At least 97
less than 10 MET hr/wk
Walking/hiking at least 10 hr/wk
Nurses’ Health Study II [17-18]
110,468 (849 cases)
27 or more
less than 3 MET hr/wk
Wu et al. 
10 MET hr/wk
† Follow-up time calculated from person-years.
‡ Additional analyses of 97,039 postmenopausal women (2,866 cases) found women whose daily routines included activities such as walking or heavy lifting/carrying had a lower risk of breast cancer than women who sat all day.
§ Additional analyses of 59,308 postmenopausal women (2,155 cases) found women who got 12 or more MET hours of physical activity per week had a lower risk of breast cancer than women who got less activity, RR was 0.86 (0.76-0.97).
|| Findings also showed a decreased risk of estrogen receptor-negative breast cancers among women with the highest levels of physical activity (more than 5 hours per week vs. inactive, RR was 0.53 (0.33-0.85)). There was no link between physical activity and risk of estrogen receptor-positive breast cancers.
¶ Estrogen receptor-positive breast cancers only. For triple negative breast cancers (307 cases), the RR was 0.77 (0.51-1.13).
** This study also found no link between physical activity at age 30 and breast cancer risk (vigorous activity vs. no activity 1.20 (0.77-1.95)), nor between physical activity at age 14 and breast cancer risk (vigorous activity vs. no activity, RR was 1.05 (0.72-1.54)).
†† Among 64,777 premenopausal women in this study, average lifetime physical activity was found to decrease the risk of breast cancer. Women who averaged at least 39 MET hours of activity a week during their lifetime had lower risk of breast cancer than inactive women, RR was 0.77 (0.64-0.93).
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