Genetic association and potential mediators between age at menarche and cholelithiasis: a two-sample two-step bidirectional mendelian randomization study

Abstract Objective Pubertal reproductive factors, such as age at menarche, have been linked to various long-term health outcomes, but their potential role in the development of cholelithiasis remains insufficiently studied. Although observational studies have suggested a possible association between menarche timing and gallstone risk, inconsistent findings and methodological limitations have left this relationship unclear. To fill this gap, we performed a bidirectional two-sample Mendelian randomization (MR) study to investigate the causal relationship between age at menarche and the risk of cholelithiasis. Methods Genome-wide association study (GWAS) genetic data were used to analyze the causal relationship between age at menarche and gallstone disease, with a two-step MR analysis performed to evaluate potential mediators. The primary analysis used inverse-variance weighted (IVW) methods, with sensitivity analyses conducted using MR-Egger regression, Cochran’s Q test, and MR-PRESSO to detect pleiotropy and heterogeneity. Results The bidirectional two-sample MR analysis indicated that earlier age at menarche was associated with an increased risk of cholelithiasis, OR 0.90 (0.82—0.99), P = 0.0369. The two-step MR analysis identified alanine aminotransferase (ALT), low-density lipoprotein cholesterol (LDL-C), and body fat percentage (BFP) as mediators, potentially influencing this association. Conclusion This study provides evidence of a causal relationship between early age at menarche and an increased risk of gallstone disease, with liver function markers, lipid metabolism, and body composition acting as mediators. These findings may inform future prevention strategies and hypothesis-driven studies to identify at‑risk individuals.