Relations of Residential Greenness with Markers of Immunity and Inflammation in the Green Heart Study

Background and Aim: Exposure to vegetation has been linked with long-term health benefits, including reduced risk of mortality, reduced cardiovascular disease, and improved mental health. However, the underlying mechanistic pathways remain poorly understood, and few studies have explored the relationship between greenness with markers of inflammation. Therefore, we examined the associations between residential greenness with circulating levels of inflammatory biomarkers and immune cells. Methods: We recruited adult participants, aged 20-70 years, from a neighborhood in Louisville, KY during the summer months of 2018 and 2019. A complete blood count panel, cytokines, and immune cells were measured in 606 participants at baseline. Surrounding greenness was assessed from Sentinel-2 satellite data by Normalized Difference Vegetation Index (NDVI) and by leaf area, within 100m and 500m buffers. To estimate associations between greenness and log-transformed outcomes we fit linear regression models adjusting for socio-demographic and behavioral risk factors. Results: Higher levels of all greenness metrics were associated with lower hsCRP, ranging from -10.6% to -17.7% lower levels of hsCRP per IQR higher greenness. Leaf area within a 100m radius was inversely associated with TNF-α (-4.0% per IQR; 95% CI: -7.3% to -0.5%), MIP-1α (- 5.65% per IQR, 95% CI: -10.93% to -0.04%), MIP-1β (-7.3% per IQR; 95% CI: -12.7% to -1.6%), while IL-6 was inversely associated within a 500m radius (-6.6%; 95% CI: -12.2% to -0.6%). In our analysis of immune cells, we found consistent inverse associations with white blood cell counts, B-cells, and monocytes with multiple metrics of greenness. Natural killer T-cells were positively associated with leaf area within a 500m radius (7.0% per IQR; 95% CI: 0.5% to 13.9%). Conclusions: Residential greenness may lower levels of inflammation and improve immune responses that could be beneficial to cardiovascular health. Keywords: vegetation, greenness, inflammation, immune cells, cytokines