Urban green spaces and mental health: Findings from Uganda

Abstract

Background: Urban green spaces (UGS) may improve mental health in high-income countries. However, evidence from low-income African countries is scarce. Here, we assessed the associations of UGS with depressive and anxiety symptoms among adult residents of Kampala District (Uganda), the potential effect modification by sociodemographic factors, and the mediation roles of social interaction, outdoor physical activity, and residential distance to major roads as a proxy of traffic-related air pollution.

Methods: We conducted a cross-sectional survey among 641 adults. We objectively measured UGS using the Normalized Difference Vegetation Index (NDVI) within buffers of 100 m and 1,000 m around the residences. We assessed the utilization of UGS as a self-reported frequency (never, occasionally, and frequently) by which individuals visited UGS in the past 6 months. The Patient Health Questionnaire-9 and the Generalized Anxiety Disorder 7-item scale were used to examine the severity of depressive and anxiety symptoms respectively. We used modified Poisson regression models to obtain prevalence ratios (PR) with their 95 % confidence intervals (CI), stratified our models, and conducted mediation analyses.

Results: We observed an inverse association between UGS and both outcomes. For example, an inter-quartile range increase in UGS within a 100 m buffer was associated with a 6 % and 8 % decrease in depressive and anxiety symptoms, respectively (PR=0.94; 95 % CI=0.89-0.99, and PR=0.92; 95 % CI=0.85-0.95, respectively). Consistently, frequent visits to UGS relative to no visits were associated with a 33 % and 35 % lower prevalence of depressive and anxiety symptoms (PR=0.67; 95 %CI=0.53-0.84, and PR=0.65; 95 %CI=0.47-0.91, respectively). Depending on the UGS metric, we observed varying potential effect modification findings by sex, age, and educational level. Finally, residential distance to major roads emerged as a mediator in the association between residential surrounding greenness and depressive symptoms.

Conclusion: Our study suggests that UGS may also improve the mental health among residents of rapidly urbanizing African low-income cities.

Keywords: Low-income countries; Mental health; Sub-Saharan Africa; Urban green spaces; Urban health.

Graphical abstract

Fig. 1

PR and 95 % CI for the relationship between NDVI buffers (100 m and 1,000 m) and depressive and anxiety symptoms with progressively increasing adjustments for confounders. Note: M1 – Controlled for between-division variability via a random effect; M2 – Controlled for socio-demographic confounders (sex, marital status, and age) on top of M1; M3 – Included educational level alongside M2.

Fig. 2

PR and 95 % CI for the association between frequency of visiting UGS [reference group: never visited UGS] and depressive and anxiety symptoms with increasing degree of adjustment of confounders Note: M1–Controlled for between-division variability via a random effect; M2 – controlled for socio-demographic confounders (marital status, sex, and age) on top of M1; M3 – Included educational level alongside M2.

Fig. 3

Adjusted PR and 95 % CI for the association between UGS metrics (NDVI 100 m, and frequency of UGS visits) and depressive and anxiety symptoms stratified by sex, age, and educational level Note: Included a random effect to account for between-division heterogeneity and controlled for age, marital status, sex, and educational level (unless stratified by potential modifier).; For frequency of UGS visits: we present for those who were frequent visitors (Reference group: those who never visited UGS).