The relationship between depressive symptoms and cognitive function in older adults: a cross-sectional study and bidirectional Mendelian randomization analysis

Observational studies have explored the association between depressive symptoms and cognitive function, but cannot determine causality. This study aims to investigate this association and assess its causality by combining cross-sectional analysis with bidirectional Mendelian randomization (MR). The cross-sectional study involved 438 older individuals from 17 villages in Jimo District, Qingdao, in 2024. We employed Poisson regression and linear regression to investigate the relationship between depressive symptoms and cognitive function, stratified by gender and age. Furthermore, two-sample bidirectional MR analysis was utilized to infer causal relationships between depression and cognitive performance, and sensitivity analysis were conducted to verify the robustness of the results. Cross-sectional analysis revealed a significant association between depressive symptoms status and higher prevalence of mild cognitive impairment (RR (95% CI): 1.28 (1.02, 1.60), P = 0.032). Concurrently, depressive symptoms status exhibited a negative correlation with lower cognitive function scores (β (95% CI): -1.23 (-2.46, 0.00), P = 0.049). The association was not affected by gender and age group. MR analysis provided suggestive evidence for a potentially negative causal relationship of depression on cognitive performance (IVW, β (95% CI): -5.72(-9.78, -1.66), P = 0.025). In conclusion, this study provided suggestive evidence for a potentially negative causal relationship between depressive symptoms and cognitive decline, indicating that preventing and treating depression may help delay cognitive decline.