Associations of change in television viewing time with biomarkers of postmenopausal breast cancer risk: the Australian Diabetes, Obesity and Lifestyle Study.

PURPOSE: Sedentary behavior has been previously shown, in a cross-sectional study, to have deleterious associations with biomarkers of postmenopausal breast cancer risk. We examined the associations of change in sedentary behavior [daily television (TV) viewing time, h/day] over a 5-year period with putative markers of postmenopausal breast cancer risk.
METHODS: The analytic cohort consisted of 1,001 postmenopausal women from the Australian Diabetes, Obesity and Lifestyle (AusDiab) study (1999-2005). Multivariate linear regression models were used to examine associations of change in TV viewing time with biomarkers of the following risk mechanisms: adiposity (body mass index [BMI], waist circumference); metabolic dysfunction (fasting plasma glucose, 2-h plasma glucose, fasting insulin, insulin resistance [homeostasis model assessment of insulin resistance (HOMA-IR)]); and inflammation (high-sensitivity C-reactive protein (hs-CRP)). All analyses were adjusted for age, baseline TV viewing, and potential confounders.
RESULTS: Hourly increments of change in TV viewing time were positively associated with BMI (β = 0.50, 95% CI 0.20, 0.81; p = 0.001), waist circumference (β = 1.18, 95% CI 0.49, 1.87; p = 0.001), fasting insulin (β = 38.13%, 95% CI 37.08, 39.20; p = 0.01) and HOMA-IR (β = 37.93%, 95% CI 36.92, 38.98; p = 0.03) in fully adjusted models. Significant associations with BMI, waist circumference, fasting insulin and HOMA-IR were also present in analyses using categories of change in TV viewing time (reduced, same, increased).
CONCLUSIONS: The findings suggest that increasing habitual sedentary behavior over time could increase breast cancer risk among postmenopausal women. Further investigation into the role of sedentary behavior in breast cancer etiology is warranted.