Abstract 1743: Sedentary behavior and breast cancer in the Black Women's Health Study
Authors: Nomura Sarah , Dash Chiranjeev , Yu Jeffrey , Palmer Julie , Rosenberg Lynn , Adams-Campbell Lucile L. 
Published: July 2016

Background: Rates of breast cancer incidence among African American women are increasingly similar to rates among Caucasian American women. Lifestyle behaviors, such as sedentary time, may contribute to differences in breast cancer incidence, but have not been well studied among African American women. Sedentary activities (physically inactive tasks that require little to no additional energy expenditure beyond basal metabolic rate) account for a large proportion of time per day in the United States and are more prevalent among African American women. Sedentary behavior may contribute to cancer risk independently of physical activity, but has not been well studied among African American women.

Objective: The objective of this study was to evaluate the association between sedentary behaviors over time on breast cancer incidence in the Black Women's Heath Study.

Methods: In this ongoing prospective cohort of African American women (analytic cohort N = 55,629), 2,482 incident breast cancer cases were diagnoses between baseline (1995) and 2013. Questionnaire data (collected every two years since 1995) was used to calculate time spent sitting. Time spent sitting at work and sitting doing recreational activities (watching TV, using internet) was summed to total sedentary time. A time-varying analytic approach was utilized (Anderson-Gill method) to reduce within-person variation and better represent long-term habits.

Results: Among women in this cohort, 23.8% reported spending &lt;5 hours/day in sedentary activities, while 8.2% reported spending 10 or more hours. A majority reported spending more than 5 hours/day sitting at work, while most women reported &lt;5 hours sitting watching TV (or related activities). Total time spent sitting was significantly associated with breast cancer incidence overall (≥10 vs. &lt;5 hours/day HR = 1.38, 95% CI: 1.16-1.65). Associations were similar for both premenopausal (≥10 vs. &lt;5 hours/day HR = 1.44, 95% CI: 1.07-1.93) and postmenopausal (≥10 vs. &lt;5 hours/day HR = 1.39, 95% CI: 1.09-1.78) breast cancer incidence. Associations remained regardless of leisure time physical activity levels and body size.

Conclusions: Our findings suggest that high sedentary time may increase risk for breast cancer among African American women. Additionally, leisure time physical activity levels and body size did not change associations, suggesting sedentary time may confer additional risk. Previously reported frequent sedentary behavior among African Americans could contribute to breast cancer disparities and should be explored further in future studies.

Citation Format: Sarah Nomura, Chiranjeev Dash, Jeffrey Yu, Julie Palmer, Lynn Rosenberg, Lucile L. Adams-Campbell. Sedentary behavior and breast cancer in the Black Women's Health Study. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 1743.