Accelerometer-measured Physical Activity and Breast Cancer Incidence in the WHI OPACH Study

Abstract

Abstract To examine the associations between accelerometer-measured physical activity (PA) and breast cancer incidence among a cohort of postmenopausal women. Methods: This longitudinal study included 6,382 women (mean age 79 ± 6 years; 49.4% non-Hispanic white, 33.7% non-Hispanic Black, 16.9% Hispanic) without a history of breast cancer who participated in the Women's Health Initiative (WHI) Objective Physical Activity and Cardiovascular Health (OPACH) Study. During 2012–2013, participants wore an ActiGraph GT3X+ accelerometer at the hip for up to 7 days. Accelerometer intensity counts were specially calibrated to PA in older women. The resulting data were used to compute minutes per day spent in total PA, light intensity PA (e.g., usual walking), and moderate-to-vigorous PA (MVPA; e.g., brisk walking). Physician-adjudicated first diagnosis of in situ (n = 18) or invasive (n = 103) breast cancer was ascertained over a median follow-up of 5.6 years. We used multivariable Cox regression to estimate covariate-adjusted hazard ratios (HRs) and 95% confidence intervals (CIs) for tertiles and one-standard deviation (SD) unit increments of PA exposures in association with breast cancer incidence. We examined effect measure modification by age, race/ethnicity, body mass index (BMI), and smoking history. Results: The highest (vs. lowest) tertile of total PA was associated with a breast cancer incidence HR of 0.67 (95% CI = 0.43–1.05) and this association was more pronounced for MVPA (HR = 0.61, 95% CI = 0.38–1.00) than for light PA (HR = 0.81, 95% CI = 0.53–1.26). In BMI-stratified analyses, HRs for total (PInteraction = 0.04) and light PA (PInteraction = 0.01), but not MVPA (PInteraction = 0.79), were stronger among women with BMI ≥ 30 kg/m2 (n cancer events = 48; total PA HRper one-SD = 0.69, 95% CI = 0.50–0.96; light PA HR = 0.69, 95% CI = 0.50–0.95) than among women with BMI < 30 kg/m2 (n cancer events = 73; total PA HRper one-SD = 1.07, 95% CI = 0.84–1.38; light PA HR = 1.13, 95% CI = 0.89–1.44). Age, race/ethnicity, and cigarette smoking history did not strongly modify these associations (PInteraction's ≥ 0.16). Conclusions: Engaging in high levels of PA may play a beneficial role in the prevention of breast cancer in older women, and in particular among postmenopausal women with BMI ≥ 30 kg/m2.