Relations of residential greenness with immunity and inflammation

Living in greener environments has been linked to lower risks of cardiovascular disease, mortality, and mental health disorders. Although these benefits have been attributed to behavioral and psychosocial pathways, emerging evidence suggests that natural environments also influence immune regulation through microbial, biochemical, and stress-modulating mechanisms. Therefore, we examined the association between residential greenspace with circulating levels of immune cells and inflammatory biomarkers.

Adult participants (ages 25-70 years) living in Louisville, KY were enrolled in the Green Heart Study (2018 - 2019). Residential greenness was quantified using leaf area index and NDVI within 100-m and 500-m buffers around participants' homes. Circulating cytokines and immune cells were measured in 624 participants at baseline. Linear regression models were used to estimate associations between greenness and each biomarker, adjusting for socio-demographic and behavioral factors.

Most participants were White (77.4%) and female (59%). Leaf area within a 100m buffer was negatively associated with circulating levels of B cells (-11.6% per IQR; 95% CI: -16.6, -6.3), monocytes (-4.7% per IQR; 95% CI: -8.9, -0.3), and natural killer cells (-5.1% per IQR; 95% CI: -9.3, -0.6). Greenness was positively associated with interleukin-4 (IL-4) (9.8% per IQR; 95% CI: 3.3, 16.7), a cytokine promoting Th2-mediated immunoregulation. Other cytokines showed no consistent associations.

Residential greenness may improve chronic inflammation and enhance immune responses by modulating both the levels of circulating immune cell populations and the signals that govern their activity. These results provide further evidence that greenness is an important determinant of cardiovascular health.