Sedentary time and breast cancer incidence in African American women
Menée aux Etats-Unis par questionnaire auprès de 46 734 participantes afro-américaines âgées de 21 à 69 ans lors de l'inclusion dans la cohorte, cette étude évalue l'association entre le temps passé en position assise, sur le lieu de travail ou à domicile, et le risque de cancer du sein
Purpose : The objective of this study was to evaluate whether time spent sitting at work or watching television was associated with breast cancer risk among African American women. Methods : The Black Women’s Health Study (analytic cohort = 46,734) is an ongoing prospective cohort study of African American women ages 21–69 at baseline (1995). Questionnaire data were used to estimate sedentary time. Total time spent sitting at work and watching television (individually and combined) at baseline and updated through follow-up (1995–2001) and breast cancer incidence (n = 2,041 incident cases, 1995–2013) was evaluated using proportional hazards regression. Results : Higher total time spent sitting at baseline (≥10 vs. <5 h/day, HR 1.27, 95 % CI 1.06, 1.53) and updated through follow-up (≥10 vs. <5 h/day, HR 1.38, 95 % CI 1.14, 1.66) was associated with an increased breast cancer risk. Associations were stronger for hormone receptor-negative tumors (≥10 vs. <5 h/day, HR 1.70, 95 % CI 1.12, 2.55) compared to hormone receptor-positive tumors (≥10 vs. <5 h/day, HR 1.16, 95 % CI 0.88, 1.52), but tests for heterogeneity were not statistically significant (p heterogeneity = 0.31). Positive associations between total time spent sitting and breast cancer incidence did not differ by physical activity level or body composition measurements. Conclusions : Our findings suggest that high sedentary time may increase risk for breast cancer among African American women.