The global, regional, and national preventable burden of depression attributable to greenness and inequalities: a scenario-based health impact analysis.

Background: Growing evidence suggests that exposure to greenness may reduce the burden of depression. Here, we quantified the global, regional, and national preventable burden of depression attributable to greenness and examined the associated socioeconomic inequalities.

Methods: We conducted a scenario-based health impact assessment using data from the Global Burden of Disease 2021 study to estimate the preventable burden of depression (measured in disability-adjusted life years (DALYs)) under three greenness expansion scenarios. We performed a random-effects meta-analysis to derive a pooled odds ratio (OR) for the association between greenness and depression, adjusting it for city-specific greenness levels to calculate the population attributable fraction for each country. We assessed temporal trends (2001-20), analysed sex differences, and quantified cross-country inequalities using the slope index of inequality and concentration index.

Results: Under the best potential scenario, the global age-standardised DALY rate (ASDR) of preventable depression per 100 000 population increased from 93.60 (95% uncertainty interval (UI) = 87.79, 99.42) in 2001 to 117.67 (95% UI = 110.61, 124.72) in 2020, with an average annual percentage change (AAPC) of 1.13% (95% confidence interval (CI) = 0.52, 1.75). Regionally, the African Region exhibited the highest growth (AAPC = 1.78%), while the Americas had the highest preventable burden in 2020 of 287.83 (95% UI = 252.67, 322.99). Moreover, the burden varied across sociodemographic index regions. Females consistently exhibited a higher preventable burden than males, with an absolute sex difference in ASDR of 54.40 (95% CI = 44.67, 64.48) in 2020. Cross-country inequalities narrowed globally, with the concentration index declining from 0.160 (95% CI = 0.088, 0.232) in 2001 to 0.051 (95% CI = -0.021, 0.123) in 2020, though regional disparities persisted.

Conclusions: Greenness expansion has the potential to significantly reduce the global depression burden, but inequitable access exacerbates mental health disparities. Targeted urban greening policies are needed to enhance mental well-being and health equity worldwide.