Sedentary time and postmenopausal breast cancer incidence

Abstract

Purpose

The objective of this study was to evaluate the prospective association between sedentary time and postmenopausal breast cancer incidence, and whether associations differ by race/ethnicity, physical activity levels, and body measurements.

Methods

The Women's Health Initiative Observational Study is a prospective cohort among women ages 50–79 years at baseline (1994–1998) (analytic cohort = 70,233). Baseline questionnaire data were used to estimate time spent sitting and total sedentary time. Associations between time spent sitting and invasive breast cancer incidence overall (n = 4,115 cases through September 2015), and by hormone receptor subtypes, were investigated using Cox proportional hazards regression. Analyses were replicated stratified by race/ethnicity, body measurements, and physical activity.

Results

Among women in this study, 34.5% reported ≤ 5 h/day sitting, 40.9% reported 6–9 h/day and 24.7% reported ≥ 10 h/day. Time spent sitting (≥ 10 vs. ≤5 h/day adjusted HR = 1.00, 95% CI 0.92–1.09) was not associated with breast cancer incidence, regardless of hormone receptor subtype. Associations did not differ by race/ethnicity, physical activity, or body measurements.

Conclusions

Results from this study do not support an association between sedentary time and breast cancer incidence.

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