Abstract
BACKGROUND: Recent studies have increasingly emphasized the robust correlation between depression and cognitive function. However, it remains unclear whether this relationship is causal or merely coincidental. To address this uncertainty, we conducted two-sample bidirectional Mendelian randomization (MR) analyses to investigate the connection between depression and cognitive performance. METHODS: We sourced genome-wide association study (GWAS) data for depression (N(SNPs)=21,306,230) from the FinnGen (R10) and for cognitive performance (N(SNPs)=10,049,954) from the IEU GWAS database. Causal effects employed methodologies such as Inverse variance weighted (IVW), weighted median, MR Egger, simple mode and weighted mode. Two-step analysis determined the contribution of the mediator variable to the outcomes. To determine stability and reliability, sensitivity analyses were performed that included an assessment of heterogeneity, horizontal pleiotropy, and the leave-one-out techniques. RESULTS: This MR analysis identified 8 independent significant SNPs associated with depression and 81 SNPs linked to cognitive performance. Our findings revealed that depression increases the risk of developing deteriorating cognitive performance (IVW β, -0.11; 95 % confidence interval (CI), -0.18 - -0.05; P(IVW) value= 5.97E-04). Conversely, cognitive performance decline could also predispose individuals to depression [odds ratio (OR)(IVW,) 0.85; 95 % CI, 0.76 - 0.95; P(IVW) value=0.004]. Multivariate MR analysis confirmed the robustness of this bidirectional association. A two-step MR mediation analysis indicated that the pathway from depression to cognitive performance is mediated by pain, with a mediation effect size of -0.022 and a mediation ratio of 28.95 %. The pathway from cognitive performance to depression is mediated by frailty, with a mediation effect value of -0.028, representing 22.40 % of the mediation proportion. CONCLUSION: A two-way causal relationship between depression and cognitive performance, with pain and frailty being mediating factors, respectively. Future research should prioritize mechanistic studies, targeted interventions, and personalized approaches to disentangle and mitigate the bidirectional effects of depression and cognitive performance.