Exploring reciprocal causation: bidirectional mendelian randomization study of gut microbiota composition and thyroid cancer

Background While an association between gut microbiota composition and thyroid cancer (TC) has been observed, the directionality and causality of this relationship remain unclear. Methods We conducted a bidirectional two-sample Mendelian randomization (MR) analysis to investigate the causal effect between gut microbiota composition and TC. Gut microbiota data were derived from a diverse population encompassing various ethnicities ( n = 18,340 samples), while TC data were sourced from an European population ( n = 218,792 samples). Instrumental variables, represented by single nucleotide polymorphisms (SNPs), were employed to assess the causal relationship using multiple MR methods, including inverse-variance weighting (IVW), weighted median, weighted mode, MR-Egger, and simple mode. F-statistics and sensitivity analyses were performed to evaluate the robustness of the findings. Results Our investigation identified a comprehensive set of 2934 instrumental variables significantly linked to gut microbiota composition ( p