Abstract / Summary
Background: Residential greenness is considered protective for mental health, but its impact on clinically diagnosed psychiatric disorders following COVID-19 remains unclear. This study investigated the association between residential greenness and risk of common mental disorders after COVID-19, and whether this relationship differed by population subgroup.
Methods: We conducted a nationwide cohort study of 3,097,179 adults aged ≥19 years with confirmed COVID-19 in South Korea between 2018 and 2023 using the K-COV-N cohort, which integrates administrative and clinical data from the National Health Insurance Service and COVID-19 data from the Korea Disease Control and Prevention Agency. Residential greenness was assessed using the normalized difference vegetation index (NDVI) and categorized as low (0.2- < 0.4), moderate (0.4- < 0.6), or high (≥0.6). The primary outcome was first diagnosis of anxiety disorder, depression, insomnia, or bipolar disorder ≥30 days post-infection. Weighted Cox proportional hazards models with inverse probability of treatment weighting were used to estimate adjusted hazard ratios (aHRs).
Results: Compared to low NDVI, moderate NDVI was associated with reduced risk of any common mental disorder (aHR, 0.97; 95% CI, 0.96-0.98), with the strongest effect for bipolar disorder (0.84; 0.79-0.88). High NDVI showed no overall benefit (1.00; 0.99-1.01) and was associated with increased anxiety risk (1.04; 1.03-1.06), especially in older adults and those with comorbidities. Younger individuals experienced the greatest benefit from moderate greenness.
Conclusion: Moderate residential greenness was linked to lower risk of mental disorders following COVID-19, while high greenness conferred limited benefit and potential risk. Greening strategies should be paired with strengthened health and social infrastructure to reduce disparities.