Greater tree cover near residence is associated with reduced allostatic load in residents of central North Carolina

Background: Among urban residents, increased contacts with nature are associated with reduced morbidity and mortality. The concept of allostatic load, a biomarker-based composite measure of physiological dysregulation, can be applied to study sub-clinical benefits of exposure, and to elucidate pathways leading to improved health. Objective: To explore associations between residential tree cover and an allostatic load index calculated using a multivariate statistical distance measure known as Mahalanobis distance. Methods: This cross-sectional population-based study involved 186 adult residents of the Durham-Chapel Hill, North Carolina metropolitan area. Measures of tree and grass cover within 500 m of residence were derived from the U.S. Environmental Protection Agency’s EnviroAtlas land cover database. Fifteen biomarkers of immune, neuroendocrine, and metabolic functions were measured in serum samples. Regression analysis was conducted using generalized additive models with thin-plate spline functions of geographic coordinates. Results: The third and second tertiles of distance-weighted tree cover were associated with 15% (95% Confidence Limits 21%; 8%) and 14% (20%; 7%) reduction in adjusted median allostatic load, respectively, compared to the first tertile. Alternatively, the corresponding effects were 0.05 (0.01; 0.35) and 0.18 (0.04; 0.80) adjusted odds ratios of having allostatic load above the 90th percentile of the study sample distribution. Grass cover was inversely correlated with tree cover and was not associated with reduced allostatic load. Conclusions: These results corroborate our previously reported finding of an inverse association between total vegetated land cover and allostatic load based on a sum of dichotomized biomarkers in the same population. These sub-clinical beneficial health effects support previously demonstrated clinical benefits of residential greenness, including reduced morbidity and mortality.

Impact/Purpose

This manuscript presents information on health-promoting community-level characteristics that supplements previous and ongoing ORD research on green spaces under the Sustainable and Healthy Communities research program. An inter-laboratory (NHEERL and NERL) team of researchers used a PIP stage 1 award to conduct an observational study in the Durham-Chapel Hill metropolitan area involving analysis of serum samples for multiple biomarkers of health effect. This is the third paper resulting from this pilot project. It demonstrates that greater amount of tree cover near residence is associated with reduced allostatic load. In this analysis, we applied a statistical technique known as Mahalanobis distance to summarize data on multiple biomarkers in a single measure of physiological dysregulation. This biomarker-based information on subclinical health benefits of urban trees is novel. The findings are important because allostatic load has been linked with increased risks of cardiovascular diseases, mental disorders, diabetes, and premature death.

Citation

Egorov, A., S. Griffin, R. Converse, J. Styles, E. Klein, J. Scott, E. Sams, E. Hudgens, AND T. Wade. Greater tree cover near residence is associated with reduced allostatic load in residents of central North Carolina. Elsevier B.V., Amsterdam, NETHERLANDS, 186:109435, (2020). [DOI: 10.1016/j.envres.2020.109435]

DOI: Greater tree cover near residence is associated with reduced allostatic load in residents of central North Carolina