Effects of Walking in Greenspace and the Built Environment in Adults with Prediabetes: A Randomized Crossover Trial

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PROJECT SUMMARY: Given the substantial adverse health and economic consequences of diabetes, preventing progression of prediabetes (prevalence of 38% in U.S. adults) to type 2 diabetes (T2D) is a major public health goal. The environment plays a critical role in determining risk for T2D. Urbanization has been associated with increased psychosocial stress and adverse health outcomes. Stress responses cause hormonal changes that lead to insulin resistance, hyperglycemia, inflammation, oxidative stress, and obesity. Increased exposure to air pollution has been associated with higher risk of diabetes and cardiovascular disease. ‘Greenspace’ is defined as publicly accessible areas with predominant naturalistic elements (e.g., trees, grass, water features, etc.). Previous studies in adults support the hypothesis that exposure to Greenspace (‘Green’) may have several health benefits relative to urban built (‘Gray’) environments. These benefits may include better autonomic functioning as assessed by improved heart rate variability (HRV), reductions in anxiety/stress, and enhanced psychological restoration, with Greenspace also serving to buffer air pollution. Walking is the most common form of moderate-intensity physical activity and has a beneficial influence on blood glucose control. Preliminary studies have suggested walking and exposure to Greenspace may act together to improve health outcomes. Yet, aside from our preliminary studies, rigorous experimental studies have not been conducted to examine how regular walking may interact with exposure to urban Greenspace, compared to urban Grayspace, to improve health. These studies are needed to investigate novel and highly generalizable strategies for “Green exercise”, capable of being implemented at the population-level to reduce the burden of disease. Therefore, we will conduct a mechanistic randomized crossover trial to compare differences in physiological, psychological, air pollution, and cardiometabolic risk measures between walking interventions completed in urban Green and Gray environments in adults with prediabetes. This multisite trial will include 180 individuals within metropolitan areas of Minneapolis/St. Paul, MN and Chicago, IL. Walking interventions will be completed in urban Green and urban Gray environments, with participants engaging in 150 minutes/week of walking for 6 weeks in each environment, separated by a 5-week washout. Specific Aims: Aim 1: Measure and compare psychosocial stress between Green and Gray walking. Aim 2: Measure and compare physiological stress over six weeks between Green and Gray walking. Aim 3: Measure real-time individual exposure to ambient particulate matter using personal air pollution monitors with GPS tracking while walking in Green and Gray environments. Aim 4: Measure individual cardiometabolic disease risk scores (index of blood glucose, insulin, lipids, systolic blood pressure, and waist) and inflammatory factors before and after 6 weeks of Green and Gray walking. Aim 5 (exploratory): Examine whether physiological, psychological, and air pollution measures mediate the differential impact of Green vs. Gray walking on cardiometabolic risk and inflammation using regression-based mediation models.