Sedentary time and breast cancer incidence in African American women
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.
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.
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.
Our findings suggest that high sedentary time may increase risk for breast cancer among African American women.
KeywordsBreast cancer Physical activity African American Sedentary time
Black Women’s Health Study
Body mass index
Estrogen receptor negative
Estrogen receptor positive
Food frequency questionnaire
Hormone receptor negative
Hormone receptor positive
Human epidermal growth factor 2 negative
Progesterone receptor negative
Progesterone receptor positive