The Green Heart Project: objectives, design, and methods.

The Green Heart Project is a controlled, community-based clinical trial to evaluate the effects of increasing greenery on community health. The study was initiated in 2018 in a low- to middle-income residential area of nearly 30 000 racially diverse residents in Louisville, KY. Community engagement was maintained throughout the project, with feedback integrated into its design and implementation. Based on land use, demographics, and greenness in the area, we designated 8 paired clusters of demographically and environmentally matched target (T) and adjacent control (C) areas (total of 16 clusters). Levels of ultrafine particles, ozone, and nitrogen oxides were measured in each cluster. In-person exams were conducted for 735 participants in wave 1 (2018-2019) and 545 participants in wave 2 (2021). Blood, urine, nail, and hair samples were collected to evaluate cardiovascular risk, inflammation, stress, and pollutant exposure. Demographic and psychosocial data were collected as well. Cardiovascular function was assessed by measuring arterial stiffness and flow-mediated dilation. After wave 2, more than 8000 mature, mostly evergreen, trees and shrubs were planted in the T clusters. After planting, data were collected during wave 3 (2022) from 561 participants. We plan to follow changes in area characteristics and participant health to evaluate the long-term impact of the greening intervention. Trial registration: ClinicalTrials.gov. Identifier: NCT03670524.