Abstract MP93: Impact of Reducing Sedentary Time on Vascular Endothelial Function in Previously Sedentary Older Adults

Background: We have previously reported that increasing habitual moderate intensity (3-6 METs) physical activity (PA) reverses aging-associated vascular endothelial dysfunction, a surrogate marker of cardiovascular risk, in previously sedentary adults ≥ 50 years old. However, whether this relationship is in part related to a reduction in sedentary time concomitant with increased PA is unknown. Methods: A post hoc analysis on data from 96 sedentary adults ages ≥ 50 years (average age 62±7 years) who participated in a randomized control trial evaluating the impact of a 12 week intervention to increase PA was performed. The intervention aimed to increase moderate intensity PA using pedometer guidance with or without the aid of an interactive website which taught participants how to integrate PA into their daily routine. Amount and intensity of PA were measured pre- and post-intervention by accelerometer. Subjects were divided into tertiles of based on change in percent of sedentary activity (< 1. 5METs) over the study period: (1) 5% or greater reduction in sedentary time, (2) 0-4.99% reduction, and (3) increase in sedentary time. Vascular endothelial function was measured by brachial artery flow mediated dilation (FMD%) prior to and at the end of a 12 week intervention period. Data were analyzed by two-way mixed ANOVA with post hoc testing as appropriate. Results: Sedentary time decreased in the study population (P=0.001), driven by a 101 minute drop in sedentary time in group 1 (N=27, 653±121 to 552±100 min, P < 0.001), a 42 minute drop in group 2 (N=29, 699±92 to 657±70 min P=0.003), and a 44 minute increase in group 3 (N=40, 629±93 to 673±120 min, P =0.02). While FMD% increased in the entire study population (P=0.008), this increase was not influences by differences in the change in sedentary time (P=0.73, group 1: 5.4±2.9 to 7.0±3.6%, group 2: 5.7±2.9 to 6.9±4.3%, group 3: 6.0±2.5 to 6.7±3.6%). No differences in endothelium-independent vasodilation were seen. Using equal tertiles for change in sedentary time or higher thresholds for reductions in sedentary time (7.5% or 10%) for group 1 did not alter these results. Conclusion: Increasing moderate intensity PA improves endothelial function in adults ≥ 50 years but this improvement is not associated with the reduction in the amount of sedentary time. Greater than a 10% reduction in the amount of sedentary time may be necessary to see its favorable impact on the vascular endothelium.