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.
Bibliographical noteFunding Information:
The authors have no conflicts of interest to disclose. This work was supported by National Cancer Institute grants R01 CA058420 (L. Rosenberg) and UM1 CA164974 (L. Rosenberg). SJON is supported by National Cancer Institute training grant 5T32CA009686-19 (A. Riegel). The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Cancer Institute or the National Institutes of Health. Data on breast cancer pathology were obtained from several state cancer registries (AZ, CA, CO, CT, DE, DC, FL, GA, IL, IN, KY, LA, MD, MA, MI, NJ, NY, NC, OK, PA, SC, TN, TX, VA), and results reported do not necessarily represent their views. The authors are grateful to the participants and staff of the BWHS.
© 2016, Springer International Publishing Switzerland.
- African American
- Breast cancer
- Physical activity
- Sedentary time