Mental health risks before the threshold: A longitudinal study of housing cost burden and depressive symptoms in South Korea.

Background: This study explores how depressive symptoms change across a gradual spectrum of housing cost burdens rather than at a single affordability benchmark. Methods: Drawing on twelve waves of the Korean Welfare Panel Study (2012-2023), we created a series of housing cost cut-offs and estimated their associations with household heads' depressive symptom scores using a panel hybrid model. Results: Findings show that depressive symptoms begin to rise once housing payments claim a modest share of income, well below the long-standing 30% guideline, and then intensify in a steady, gradual pattern as the burden grows. The association between housing cost burden and depressive symptoms becomes statistically significant at an 11% threshold and remains significant up to the conventional 30% benchmark. The most pronounced effect is observed near the 27% burden cut-off. Tenure-specific analyses further indicated that this graded association was concentrated primarily among renters. Conclusions: Our results indicate that mental health risks emerge at moderate cost levels and build progressively, suggesting that policies attuned to the early stages of housing cost strain may help prevent psychological distress from becoming entrenched.