Causal Links Between the Plasma Lipidome and Cognitive Performance: Targets, Pathways, and Lifestyle Influences

The plasma lipidome has been implicated in brain health, yet whether specific lipid species exert causal effects on cognitive performance (CP) remains uncertain. We integrated whole-blood expression quantitative trait loci (eQTL) with CP genome-wide association studies using summary data-based Mendelian randomization (SMR) with heterogeneity in dependent instruments (HEIDI), followed by Gene Ontology and Kyoto Encyclopedia of Genes and Genomes enrichment. Two-sample Mendelian randomization (MR) estimated effects of 179 plasma lipid species on CP using inverse-variance weighted primary analysis. Two-step MR quantified mediation via 43 modifiable lifestyle and biochemical factors. Mendelian randomization phenome-wide association study (MR-PheWAS) assessed systemic consequences and potential pleiotropy. Using SMR with blood eQTLs and HEIDI test, we identified 1066 genes associated with CP enriched for lipid metabolism and membrane functions implicating phosphoinositide signaling. Two-sample MR analyses demonstrated heterogeneous causal effects of phosphatidylcholine-ether (PC-O) species on CP, with PC (O-16:0_20:3) positively associated with CP, whereas PC (O-18:1_18:2) (P = 0.025, OR = 0.984 (95% CI 0.969-0.998)) and PC (O-18:2_16:0) (P = 0.027, OR = 0.984 (95% CI 0.970-0.998)) showed adverse effects. Sphingomyelin (SM) (d36:1) exhibited a robust positive association with CP (P < 0.001, OR = 1.026 (95% CI 1.014-1.039)), remaining significant after sensitivity analyses. Fourteen modifiable factors associated with CP. HDL-C increased SM (d36:1) and PC (O-16:0_20:3) favoring CP, whereas poultry intake increased PC (O-18:1_18:2) impairing CP. SMR and MR support causal links between plasma lipids and CP. SM (d36:1) and select ether PCs emerge as candidate biomarkers or pathway mediators. These findings suggest that lipid-centered metabolic modulation may represent a potential strategy for preserving cognitive health, with lifestyle-related influences providing further support for integrated preventive approaches.