Standing Breaks During Prolonged Sitting Improve Glycemic Control And Endothelial Function: A Crossover Laboratory Trial

Purpose: Older adults are less likely to meet physical activity guidelines and spend more time sitting than younger adults. Aging adults have elevated cardiometabolic disease and cancer risk, which can be exacerbated in postmenopausal women due to hormonal shifts and increased adiposity. The postural change of standing increases muscle contractions and arterial blood flow and induces compensatory changes in heart rate and blood pressure. Thus, interrupting prolonged sitting with brief standing breaks may be a feasible approach to improve aging-associated metabolic and vascular health outcomes. Methods: Postmenopausal women with overweight or obesity (n = 79; age 67 ± 7y) were enrolled in a three-condition, randomized crossover trial. Participants completed three supervised, 5-h experimental conditions: Prolonged sitting (Control), frequent Sit-to-Stands (STS - 2 min stand every 15 min), and Hourly Standing Breaks (HSB - 8 min stand every hour). Each standing break condition included 40 min of total standing time but varied in number and duration of breaks. Standardized liquid meals were consumed at 0 min (M1) and 180 min (M2). Blood samples were collected across the condition periods to determine the incremental area under the curve (iAUC) for glucose and insulin during the total and post-meal periods: 0-300 min, 0-120 min, and 180-300 min. Condition impact on superficial femoral artery endothelial function was assessed using flow-mediated dilation (FMD). Linear mixed models compared iAUC and FMD ratio (5 h-to-baseline) values between experimental and control conditions. Results: There was no evidence of between-condition differences (p > 0.05) for insulin and glucose iAUCs from 0-300 min. However, STS significantly lowered 2-hr postprandial blood glucose excursion after M2 compared to after M1 by -13.4% (p = 0.04). Control and HSB had significantly higher 2-hr postprandial insulin excursions after M2 compared to after M1 (+10.9%, p = 0.03; +11.5%, p = 0.02, respectively). Both STS and HSB significantly mitigated the negative effect of prolonged sitting on FMD-measured endothelial function observed in the control (+17.9%, p < 0.001 and + 22.5%, p < 0.001, respectively). Conclusion: Brief, low-intensity interruptions of sitting time with standing acutely improves endothelial functioning in older women. Supported by: National Institute of Aging (P01 AG052352) and National Center for Advancing Translational Sciences (UL1TR001442)