Causal association of TSH with ischemic heart diseases and heart failure: A 2-sample Mendelian randomization study

Thyroid dysfunction is associated with the risk of cardiovascular disease; however, whether plasma thyroid-stimulating hormone (TSH) levels in subjects with euthyroidism affect the risk of cardiovascular disease remains unclear. This study aimed to investigate the causal association between plasma TSH levels and cardiovascular diseases, particularly ischemic heart disease and heart failure (HF). Summary statistics from the Integrative Epidemiology Unit Open genome-wide association studies Project and FinnGen consortium were used to investigate the causal relationship between plasma TSH levels and the risk of cardiovascular diseases. Two-sample Mendelian randomization analysis using inverse-variance weighting as the primary method was performed. The MR Pleiotropy RESidual Sum and Outlier and leave-one-out methods were used to ensure the robustness of our findings. Genetically determined plasma TSH levels were associated with major coronary heart disease events (OR 1.0557, 95% CI 1.0141-1.0991), all-cause HF (OR 0.9587, 95% CI 0.9231-0.9956), and HF + non-ischemic cardiomyopathy (OR 0.9318, 95% CI 0.8786-0.9882). After the Bonferroni correction, the causation described above disappeared. In the secondary analysis, genetically determined higher TSH levels were associated with a higher risk for unstable angina pectoris (OR 1.0913, 95% CI 1.0350-1.1507), but were associated with a lower risk for HF + overweight (OR 0.9265, 95% CI 0.8821-0.9731). These results were further validated using sensitivity analysis. Our findings show that increased plasma TSH levels in patients with euthyroidism may increase the risk of unstable angina pectoris but reduce the risk of HF in overweight patients. This evidence indicates that plasma TSH levels may need to be carefully controlled in specific patients.