Abstract 055: Sedentary Screen Time is Associated with Higher Left Ventricular Mass and Posterior Wall Thickness in the Coronary Artery Risk Development in Young Adults (CARDIA) Study
Introduction: Sedentary time is a novel risk factor that could affect health outcomes, independently from moderate and vigorous physical activity. Screen time (watching TV or using a computer recreationally) is a major contributor to sedentary time and a potential target for intervention. Relationships between screen time and measures of cardiac structure and function, which predict cardiovascular outcomes, have not been studied.
Hypothesis: We hypothesized that greater screen time would be related to higher left ventricular mass (LVM), posterior wall thickness (PWT), relative wall thickness, and end diastolic volume and lower end systolic volume after controlling for moderate and vigorous physical activity.
Methods: This was a cross-sectional analysis of 2,866 CARDIA participants without a history of heart disease at the 25-year follow-up visit (2010-2011). Average sedentary screen time was measured by questionnaire and measures of cardiac structure and function by echocardiography(ECHO). Generalized linear models evaluated trends for ECHO measures across higher categories of screen time after adjustment for demographics, smoking, alcohol, and moderate and vigorous physical activity. This was repeated within quartiles of moderate and vigorous physical activity. Further models adjusted for potential mediators (SBP, DBP, hypertensive medication use, diabetes, and then BMI) of the relationships between sedentary time and ECHO measures. Results: Participants were aged 43-55 years, 58% female, and had a mean BMI of 29.5±6.7 kg/m2. Median screen time was 2.9 (IQR 1.8, 4.3) hours/day. A significant positive relationship was observed where higher screen time was associated with higher LVM/height2.7 (P for trend = 0.001) and PWT (P for trend = 0.028), even after adjustment for moderate and vigorous physical activity. Within quartiles of physical activity, higher screen time was not associated with LVM/height2.7 in the lowest quartile (P for trend = 0.855) but was in the higher quartiles (P for trend = 0.005, 0.050, and 0.027 in quartiles 2, 3, and 4, respectively). When SBP, DBP, hypertensive medication use and diabetes were added to the model, the associations were attenuated, but remained between screen time and LVM/height2.7 (P for trend=0.017), although not for PWT (P for trend=0.183). These associations were substantially attenuated following further adjustment for BMI (P for trend = 0.758 and 0.775, respectively). Other ECHO measures were not associated with screen time.
Conclusions: Sedentary screen time is independently associated with higher LVM/height2.7 and PWT, even after adjustment for moderate and vigorous physical activity. These associations were no longer observed after adjustment for BMI, suggesting that the associations between sedentary time and increased LVM and PWT are mediated by adiposity.
- © 2013 by American Heart Association, Inc.