Abstract 006: Relationship of Sedentary Behavior and Physical Inactivity to Incident Coronary Heart Disease: Results from the Women's Health Initiative

Abstract

Background: Sedentary behavior, such as prolonged sitting, is becoming recognized as a distinct construct that may not merely reflect lack of leisure-time physical activity (PA), usually defined as physical inactivity. Our objective was to examine the independent and joint associations of sedentary time and physical inactivity with risk of incident coronary heart disease (CHD) in women. Methods: This study included 84,798 post-menopausal women, aged 50-79 and free of CHD at baseline, participating in the Women's Health Initiative Observational Study. At baseline, participants reported information on sedentary behavior, defined as hours of sitting and lying per day, and usual PA, defined as energy expenditure from recreational activity including walking, mild, moderate and strenuous PA. Participants were followed from the baseline visit through September 2010 for first occurrence of CHD (MI and CHD death). Cox regression models were used to estimate hazard ratios (HR) and 95% confidence intervals (CI) for incident CHD according to tertiles of sedentary time (hrs/day) and physical activity (MET-hrs/wk). Results: Sedentary time ≥10 hrs/day was associated with increased CHD risk (HR=1.13, 95% CI 1.04,1.23) in age-adjusted models, but was non-significant in multivariable-adjusted models (HR=1.08, 95% CI 0.99,1.17). In multivariable-adjusted models, the HR of CHD comparing moderate (5.1 - 16.25 MET-hrs/wk) and low (≤ 5 MET-hrs/wk) levels of PA to high (>16.25 MET-hrs/wk) levels were 1.10 (95%CI 1.01,1.21) and 1.21 (95%CI 1.11,1.32), respectively (P for trend <.0001). When we cross-classified women by sedentary time and PA (P for interaction = 0.91), CHD risk was significantly increased only in women with low PA regardless of their sedentary behavior, with the greatest risk seen in women reporting low PA and ≥10 hrs/day of sedentary time. Conclusion: Physical inactivity is associated with increased CHD risk in a dose-response manner, whereas sedentary behavior was only modestly associated with CHD risk in this analysis. Physical Activity (MET-hours/week) Sedentary Time (hours/day) High (> 16.25) Moderate (5.1 - 16.25) Low (≤ 5) ≤6 1.00 (Referent) 1.12 (0.96, 1.30) 1.17 (1.01, 1.36) 6.1-9.9 0.96 (0.82, 1.13) 1.09 (0.94, 1.27) 1.18 (1.02, 1.38) ≥10 1.08 (0.92, 1.27) 1.14 (0.99, 1.32) 1.32(1.15, 1.51) The multivariable model includes age, race, education, income, marital status, smoking, family history of MI, depression, alcohol intake, and history of diabetes, hypertension, or hypercholesterolemia