New research highlights an important link between obesity and breast cancer risk in postmenopausal women. A large systematic review and meta-analysis published in The Breast found that higher body mass index (BMI) is associated with a significantly increased risk of estrogen receptor (ER)–positive breast cancer after menopause, particularly among women who are not using hormone replacement therapy (HRT). The analysis included data from 33 studies involving over two million women, providing robust evidence of the relationship between body weight and hormone-related cancer risk.

      Among postmenopausal women, both overweight and obesity were associated with increased risk of ER-positive breast cancer, with obesity showing a stronger effect. The association was even more pronounced in women who had not used hormone replacement therapy. In contrast, no consistent relationship was found between obesity and ER-negative or triple-negative breast cancer. Interestingly, patterns differed in premenopausal women, where overweight was linked to a lower risk of ER-positive breast cancer but a higher risk of ER-negative and triple-negative disease. Researchers suggest these differences likely reflect variations in hormonal environments before and after menopause.

      These findings underscore the broader health impact of obesity beyond metabolic disorders, highlighting the importance of maintaining a healthy body weight as a key strategy for reducing cancer risk in postmenopausal women. The study also reinforces the complex interaction between hormones, body fat, and cancer biology across different stages of life.