Association of neighborhood greenness with self-perceived stress, depression and anxiety symptoms in older U.S adults

Abstract

Background: Neighborhood environment, such as green vegetation, has been shown to play a role in coping with stress and mental ill health. Yet, epidemiological evidence of the association between greenness and mental health is inconsistent.

Methods: We examined whether living in green space is associated with self-perceived stress, depressive and anxiety symptoms in a nationally representative, longitudinal sample of community-dwelling older adults (N = 4118; aged 57-85 years) in the United States. We evaluated perceived stress, depression and anxiety symptoms using the Cohen's Perceived Stress Scale, the Center for Epidemiological Studies - Depression, and the Hospital Anxiety and Depression Scale - anxiety subscale, respectively. Greenness was assessed for each participant using the Normalized Difference Vegetation Index at 250-m resolution, as well as a buffer of 1000-m. We conducted longitudinal analyses to assess the associations between greenness and mental health upon adjusting for confounders (e.g., education), and to examine potential mediation and effect modification.

Results: An interquartile range (0.25 point) increase in contemporaneous greenness was significantly associated with 0.238 unit (95% CI: - 0.346, - 0.130) and 0.162 unit (95% CI: - 0.271, - 0.054) decrease in the perceived stress in base and multivariable models, respectively. The magnitude of the association was similar or even stronger when examining summer (- 0.161; 95% CI: - 0.295, - 0.027) and annual average of greenness (- 0.188; 95% CI: - 0.337, - 0.038), as well as greenness buffer of 1000-m. The greenness-stress association was partially mediated by physical activity (15.1% mediated), where increased greenness led to increased physical activity and less stress, and by history of respiratory diseases (- 3.8% mediated), where increased greenness led to increased respiratory disease and more stress. The association was also significantly modified by race, social support, physical function, socioeconomic status, and region. While greenness was not significantly associated with anxiety and depressive scores across all participants, significant inverse associations were found for Whites participants, and for individuals with higher socioeconomic status, who were physically active, as compared to their counterparts.

Conclusion: We found a direct association of greenness with perceived stress among older adults, and an indirect association mediated through physical activity and respiratory disease history. Our study findings warrant further examination of the mediation and modification of the greenness-mental health association.

Keywords: Anxiety; Depression; Effect modification; Green space; Mediation; Perceived stress.

Fig. 1

Mean difference (95% CI) for increment in contemporaneous greenness (at 250-m buffer) and a) perceived stress, b) anxiety symptoms, and c) depressive symptoms among NSHAP participants, stratified by effect modifiers in multivariable models^1,2. ¹ Multivariable models adjusted for age, gender, questionnaire year and season, region, education attainment, 3-day moving average of temperature and 60-months moving average of PM_2.5. ² First category of each modifier as reference group; daggers represent statistically significant effect modification (p-interact < 0.05)

Fig. 2

DAG demonstrating the relationship among contemporaneous greenness, perceived stress and their mediators, confounders, and effect modifiers. Pathway a represents of the direct, unmediated, association between greenness and perceived stress. Pathway b demonstrates the role of mediators, in which greenness has an indirect effect of which respiratory disease history and physical activity are on the causal pathway. Pathway c shows the effect modifiers that modify the greenness’ effect on the perceived stress. Pathway d depicts the presence of confounders because they predict both the greenness and stress