OBJECTIVE: The study aimed to investigate the causal relationship between serum 25-hydroxyvitamin D (25(OH)D) levels and epilepsy using Mendelian randomization (MR), thereby addressing confounding and reverse causality issues in observational studies. METHODS: We employed a two-sample bidirectional MR design utilizing summary-level data from the IEU OpenGWAS project. Serum 25(OH)D levels were analyzed using the publicly available dataset ebi-a-GCST90000618, which included 496,946 European samples and 68,960,93 SNPs. Data on epilepsy were obtained from ebi-a-GCST90028840, comprising 458,310 samples, including 4,382 epilepsy patients and 453,928 controls. To identify instrumental variables (IVs), we applied a significance threshold of P <
5e-8 for serum 25(OH)D levels as the exposure and P <
5e-6 for epilepsy as the exposure. IVs were required to demonstrate an r RESULTS: Both directions of the MR analysis revealed no genetic correlation between serum 25(OH)D levels and epilepsy. CONCLUSION: Our findings, supported by robust IV screening and consistent results across multiple MR methods, indicate a lack of causal relationship between serum 25(OH)D levels and epilepsy. These results suggest that while vitamin D plays a role in the nervous system, its relationship to epilepsy may not be direct, thus highlighting the need for further investigation in future studies.