The Relationship and Mechanisms Between Body Mass Index and Autoimmune Hypothyroidism: Insights from Mendelian Randomization.

Background: Obesity is increasingly prevalent worldwide and has been linked to various health conditions, including hypothyroidism.

Methods: Summary-level GWAS data from the UK Biobank and the FinnGen Biobank were used for Mendelian randomization analysis. The impact of BMI on autoimmune hypothyroidism through putative mediators was assessed through a four-step analytical process. Statistical analyses, including the inverse-variance-weighted (IVW) method, weighted median (WM), and MR-Egger methods, were employed to evaluate causal relationships and detect horizontal pleiotropy. Mediation analysis was performed using a two-step method to assess the causal relationships between BMI, putative mediators, and autoimmune hypothyroidism.

Results: Higher BMI was associated with an increased risk of autoimmune hypothyroidism. Mean corpuscular volume, eosinophil count, and cystatin C levels were found to mediate this association.

Conclusions: BMI positively correlates with autoimmune hypothyroidism, with mean corpuscular volume, eosinophil count, and cystatin C levels mediating this relationship. Further research is needed to confirm these findings and explore causal relationships across diverse populations.