Nexus between residential air pollution and physiological stress is moderated by greenness

Urban living is synonymous with a higher exposure to environmental stressors such as air pollution and associated physiological stress; however, the modifying role of greenness has been understudied. We included 190,200 participants from a UK-wide cohort to examine the modifying role of residential greenness on associations between air pollutants and composite physiological stress (CPS) constructed from 13 biomarkers of three physiological functions and two organs. We found that living in areas with higher air pollutants was associated with higher CPS, whereas higher residential greenness was inversely associated with CPS. Relative to participants exposed to low air pollution and high greenness (least-impacted group), those exposed to high air pollution and low greenness (double-impacted group) had higher odds of their CPS being in the highest quartile (22% (95% confidence interval (CI): 12–31%) for PM_2.5, 18% (95% CI: 9–28%) for PM₁₀, 17% (95% CI: 7–27%) for PM_2.5–10 and 13% (95% CI: 4–23%) for NO_x), with evidence of synergistic interactions between the pollutants PM₁₀, PM_2.5–10 and NO_x and greenness exposures on the risk of high CPS. Considerable between-city variability was observed. The evidence points to the need for nature-based interventions, such as optimizing urban greenness for healthy cities with lower stress levels and related health burdens.