Body Mass Index: Its Evolving Impact on Breast Cancer Risk Post-Menopause
This research focuses on how body mass index (BMI) influences breast cancer risk around menopause, discovering that BMI’s impact shifts notably after menopause. Before menopause, higher BMI is linked with a reduced risk of breast cancer. However, post-menopause, the trend reverses, with higher BMI showing a potential increase in risk. The study, which tracked over 600,000 women, utilized varying statistical models to accurately determine this transition, emphasizing the period around menopause as critical for understanding cancer risk dynamics.
The findings highlight the complexity of how body weight and fat distribution affect breast cancer risk during a woman’s life, particularly around menopause. The best-fit statistical model suggested a constant risk pattern during the studied age range, with an increasing risk only becoming evident after age 55. This nuanced understanding could aid in developing targeted prevention strategies that consider weight management as part of breast cancer risk reduction, especially for women approaching menopause.
Understanding these patterns helps tailor public health advice and personal health strategies, potentially leading to interventions that mitigate breast cancer risk based on individual BMI trajectories. By focusing on the timing of these risk changes, the research provides a basis for future studies aiming to uncover the underlying mechanisms that link BMI and cancer risk during the menopausal transition.
Article Information
BMI and breast cancer risk around age at menopause
Published in: Cancer Epidemiology, Ann Von Holle et al.
Abstract
Background: A high body mass index (BMI, kg/m2) is associated with decreased risk of breast cancer before menopause, but increased risk after menopause. Exactly when this reversal occurs in relation to menopause is unclear. Locating that change point could provide insight into the role of adiposity in breast cancer etiology.
Methods: We examined the association between BMI and breast cancer risk in the Premenopausal Breast Cancer Collaborative Group, from age 45 up to breast cancer diagnosis, loss to follow-up, death, or age 55, whichever came first. Analyses included 609,880 women in 16 prospective studies, including 9956 who developed breast cancer before age 55. We fitted three BMI hazard ratio (HR) models over age-time: constant, linear, or nonlinear (via splines), applying piecewise exponential additive mixed models, with age as the primary time scale. We divided person-time into four strata: premenopause; postmenopause due to natural menopause; postmenopause because of interventional loss of ovarian function (bilateral oophorectomy (BO) or chemotherapy); postmenopause due to hysterectomy without BO. Sensitivity analyses included stratifying by BMI in young adulthood, or excluding women using menopausal hormone therapy.
Results: The constant BMI HR model provided the best fit for all four menopausal status groups. Under this model, the estimated association between a five-unit increment in BMI and breast cancer risk was HR=0.87 (95% CI: 0.85, 0.89) before menopause, HR=1.00 (95% CI: 0.96, 1.04) after natural menopause, HR=0.99 (95% CI: 0.93, 1.05) after interventional loss of ovarian function, and HR=0.88 (95% CI: 0.76, 1.02) after hysterectomy without BO.
Conclusion: The BMI breast cancer HRs remained less than or near one during the 45-55 year age range indicating that the transition to a positive association between BMI and risk occurs after age 55.
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