Causal relationship between hyperthyroidism and cataracts: a two-sample bi-directional mendelian randomization study

Clinical studies and meta-analyses have suggested a link between thyroid dysfunction and lens opacification. The objective of this study is to investigate the causal relationship between hyperthyroidism and the development of cataracts using the Mendelian randomization approach, with the aim of filling the gap in knowledge about the systemic effects of hyperthyroidism on ocular health. Leveraging genetic variants as instrumental variables, the analysis used extensive datasets from the UK Biobank and the FinnGen Database and employed three common approaches for causal inference (the Inverse Variance Weighted method, a regression based method the Weighted Median estimator, and MR-Egger regression) and accompanying sensitivity analyses to ensure robustness. The results demonstrate that there is a strong likely causal relationship, with hyperthyroidism increasing the risk of developing senile cataracts (OR = 361.09, 95%CI 5.024 to 2.60 × 10⁴, P = 0.007). A sensitivity analysis provided no evidence of horizontal pleiotropy and no significant outliers, suggesting the results are robust. In conclusion, our study established a significant causal relationship between hyperthyroidism and increased risk of cataract development, underscoring the importance of considering the systemic effects of hyperthyroidism in clinical and public health interventions and policies. Future research should focus on elucidating the molecular mechanisms underlying this association, exploring the potential benefits of early intervention in hyperthyroidism to prevent cataract development, and investigating whether these findings translate across different ethnic populations. Additionally, further GWAS studies aimed at identifying genetic variants associated with both hyperthyroidism and cataracts are warranted to confirm and expand upon our results.