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: Many studies have shown weight gain in adulthood increases the risk of breast cancer in postmenopausal women. To date, only a few studies have looked at weight gain and premenopausal breast cancer and results have been mixed.
Menopausal hormone therapy (MHT) may mask the true effect weight has on breast cancer risk. Thus, the increase in risk from being overweight or obese seen in MHT users is lower than that seen in non-users. This does not mean MHT protects against breast cancer. Rather, the increased risk of breast cancer from MHT is likely masking the increase in risk from body weight. For this reason, many studies report findings by MHT use.
Learn more about weight gain 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.
Read Komen’s perspective on body weight and breast cancer risk(September 2011).*
* 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 Therefore, some information may be out of date at this time.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 studies with at least 1,000 breast cancer cases and meta-analyses. Table note: Relative risk above 1 indicates increased risk. Relative risk below 1 indicates decreased risk.
Study Population(number of participants)
Time of Weight Gain
Categories of Weight Gain Compared
Relative Risk of Breast Cancer in Women who Gained the Most Weight Compared to Women who Gained the Least RR (95% CI)
Prospective cohort studies
Nurses' Health Study 
From age 18
11-22 lbs.vs.little weight change (less than 4.4 lbs. gain or loss)
22-44 lbs. vs.little weight change
44-55 lbs. vs.little weight change
More than 55 lbs.vs.little weight change
From age at menopause
22 lbs. or morevs.little weight change
Multiethnic Cohort 
From age 21
Iowa Women's Health Study 
29-45vs.13 lbs. or less
More than 45vs.13 lbs. or less
Age 55-64: 1.47 (1.13-1.91) Age 65-74: 1.78 (1.52-2.08) Age 75-84: 1.79 (1.40-2.30)
NIH-AARP Diet and Health Study 
66-88 lbs.vs.little weight change (+/- 4.2 lbs.)
From age 50
Between ages 35 and 50
Cancer Prevention Study-II (CPS-II) 
71 lbs. or morevs. little weight change
Nurses' Health Study and Nurses' Health Study II 
33-43.9 lbs.vs. little weight change
44-54.9 lbs.vs. little weight change
EPIC Cohort 
From age 20
More than 44 lbs. vs. little weight change (+/- 4.4 lbs.)
21-40vs. 5-20 lbs.
Ductal carcinoma: 1.28 (1.08-1.53)||
Lobular and mixed ductal/lobular carcinoma:0.99 (0.70-1.39)||
41-60vs. 5-20 lbs.
Ductal carcinoma: 1.65 (1.37-2.00)||
Lobular and mixed ductal/lobular carcinoma:1.08 (0.73-1.61)||
61 or morevs. 5-20 lbs.
Ductal carcinoma: 1.89 (1.53-2.34)||
Lobular and mixed ductal/lobular carcinoma:1.54 (1.01-2.33)||
Black Women’s Health Study 
55 or morevs. less than 22 lbs.
Women's Health Initiative 
BMI change more than 9.7vs.no BMI change
Vrieling et al. 
From age 18**
For ER+/PR+ tumors:2.33 (2.05-2.60)
For ER-/PR- tumors:1.34 (1.06-1.63)
ER+ = estrogen receptor-positive
ER- = estrogen receptor-negative
PR+ = progesterone receptor-positive
PR- = progesterone receptor-negative
† Weight gain increased breast risk more in postmenopausal women not taking MHT than in those currently taking MHT. Among women who were not taking MHT, the relative risk of breast cancer with a weight gain of 55 pounds was 1.98 (1.55-2.53). Among women who were currently taking MHT, the relative risk with a weight gain of 55 pounds or more was 1.20 (1.01-1.43).
‡ Weight gain increased breast cancer risk more in postmenopausal women who never used MHT and in women who took MHT in the past than in those currently taking MHT. Among never users, a weight gain of 50 or more pounds had a relative risk of 1.60 (1.36-1.87) and among past users, 1.60 (1.27-2.01). Among women currently taking MHT, a weight gain of 50 or more pounds had a relative risk of 1.14 (0.97-1.35).
§ Among women not currently taking MHT. Among women using MHT, there was no increase in risk from weight gain.
|| Among women who had never used MHT.
¶ Among women who were not currently taking MHT, weight gain of more than 44 pounds compared to little weight change increased risk of breast cancer, 1.52 (1.08-2.13). This increased risk was not seen in women who were currently taking MHT.
** Five of seven studies measured weight gain from age 18. One study measured weight gain from age 20 and one study measured from age 50.
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