Accelerometer-based measures of active and sedentary behavior in relation to breast cancer risk

Epidemiologic studies suggest that physical activity reduces breast cancer risk by 20–40 %. However, prior studies have relied on measures of self-report. In a population-based case–control study, we evaluated accelerometer measures of active and sedentary behavior in relation to breast cancer among 996 incident cases and 1,164 controls, residents of Warsaw, Poland (2000–2003), who were asked to wear an accelerometer for 7 days. Accelerometer values were averaged across valid wear days and summarized as overall activity (counts [ct]/min/day); in minutes spent in sedentary behavior (0–99 ct/min); and light (100–759 ct/min) and moderate-to-vigorous (760+ ct/min) activity. Odds ratios (OR) and 95 % confidence intervals (CI) were estimated using unconditional logistic regression. Comparing women in the highest quartile (Q4) of activity to those in the lowest (Q1), time spent in moderate-to-vigorous activity was inversely associated with breast cancer odds after adjustment for known risk factors, sedentary behavior and wear time (ORQ4vsQ1 0.39, 95 % CI 0.27–0.56; P-trend < .0001). Sedentary time was positively associated with breast cancer, independent of moderate-to-vigorous activity (ORQ4vsQ1 1.81, 95 % CI 1.26-2.60; P-trend = 0.001). Light activity was not associated with breast cancer in multivariable models including both moderate-to-vigorous activity and sedentary behavior. Our findings support an inverse association between accelerometer-based measures of moderate-to-vigorous physical activity and breast cancer while also suggesting potential increases in risk with sedentary time.