BACKGROUND: While greater social engagement is often associated with a reduced risk of depression, longitudinal studies that account for diverse social structures and cultural contexts among middle-aged or older are limited. METHODS: This study utilized cohort data from the Korean Longitudinal Study of Ageing (n=11,174
2006-2020) in South Korea (KR), the Health and Retirement Study (n=42,405
2004-2019) in the US, and the English Longitudinal Study of Ageing (n=28,624
2002-2019) in the UK, including a total of 29,378 individuals from the population aged ≥45 years. Social engagement frequency was categorized into infrequent, intermediate, and frequent, with changes classified as unchanged, increased, or decreased. The primary outcome was the onset of depression, assessed using the CES-D Scale. Hazard ratios (HR) and 95% confidence intervals (CI) were estimated using a Cox proportional hazards regression model. RESULTS: In the KR cohort, increased social engagement significantly reduced depression risk only in the infrequent group (KR: HR, 0.20 [95% CI, 0.14-0.28]). However, decreased social engagement elevated depression risk in both the intermediate group (KR: 6.92 [3.73-12.83]
US: 1.44 [1.16-1.79]) and the frequent group (KR: 1.50 [1.30-1.74]
US: 1.24 [1.13-1.38]). Conversely, in the UK cohort, increased social engagement raised depression risk in the infrequent group (UK: 1.35 [1.01-1.79]) and intermediate group (UK: 1.63 [1.17-2.27]), while decreased engagement lowered depression risk only in the frequent group (UK: 0.80 [0.71-0.90]). DISCUSSION: We observed notable national variations in the association between social engagement and depression risk, influenced by cultural and political differences.