Residential greenspace modifies the effect of road traffic noise exposure on mental health in youth

Abstract

Background Urban road traffic noise exposure is associated with poor mental health, causing stress and impeding restoration. On the other hand, urban greenspace may improve mental health through enhanced neighbourhood restorativeness and consequent stress reduction. This study aimed to determine whether greenspace modified the effect of road traffic noise on mental health. Methods In 2016 we conducted a cross-sectional survey among 399 school/university students (17.9±2.3 age; 67.9% men) who reported their address in the city of Plovdiv, Bulgaria. 24-hour road traffic noise exposure (Lden) at home was estimated based on an European Noise Directive map. Two greenspace indicators were tested as potential moderators: tree cover density (in 500m buffer), calculated at a resolution of 20m, and the Euclidean distance to the nearest urban greenspace, calculated from Open Street Maps. Mental health was measured by the 12-item General Health Questionnaire. Using the Johnson-Neyman procedure, we identified the values along the continuous moderators where the linear relationship between Lden and mental health transitioned between statistically significant to nonsignificant. Results Lden was associated with poorer mental health only in students with <6% tree cover in the neighbourhood (β = 0.77; 95% CI: 0.06, 1.49) and in those living at 300–600m from the nearest greenspace (0.73; 0.03, 1.44). Lden had no significant effect in those living <300m or > 600m from an urban greenspace. Conclusions Living in a neighbourhood deprived of trees seemed to enhance the negative effect of road traffic noise on mental health. Residing very close or far from an urban greenspace also appeared to be beneficial, probably reflecting the access to an urban restorative environment, in the first case, or closer to natural/agricultural greenspace in the periphery of the city, in the second case. There is need to enhance the access to restorative environments through better greenspace policy. Key messages: Greenness enhances the restorative quality of urban environments. Noise is associated with poor mental health when greenness is scarce.