Thyroid Function Impact on Cardiac Structure, Function and Disease Risk: Evidence of Causal Associations in European Ancestry

Abstract

BackgroundThyroid hormones play a crucial role in cardiovascular physiology. Subclinical thyroid dysfunction has been associated with adverse cardiovascular outcomes, but evidence is mixed regarding causality. ObjectiveTo investigate the potential causal relationships of thyroid-stimulating hormone (TSH), free thyroxine, hypothyroidism, and hyperthyroidism with cardiovascular outcomes, including atrial fibrillation (AF), coronary artery disease, myocardial infarction, heart failure, and ischemic stroke, as well as their impact on cardiac structure and function assessed by cardiac magnetic resonance imaging. MethodsA comprehensive two-sample Mendelian randomization (MR) analysis was conducted, utilizing summary data from large-scale meta-analyses of European ancestry individuals. ResultsGenetically determined lower TSH levels (OR 0.928, 95% CI: 0.884 to 0.974, P = 0.003) and genetic risk of hyperthyroidism (OR 1.049, 95% CI: 1.016 to 1.083, P = 0.003) were associated with increased AF risk. These associations remained significant even after adjusting for cardiovascular risk factors. Colocalization and multivariable MR revealed height as a key mediator between TSH/hyperthyroidism and AF. These findings were further corroborated in the independent FinnGen cohort. However, no clear evidence was found for relationships between thyroid function and other cardiovascular outcomes and cardiac structure and function. ConclusionsOur study shows that reduced TSH levels and hyperthyroidism heighten AF risk, with height serving as an important mediator in these associations. The primary focus of thyroid management in cardiovascular health should be on preventing and treating arrhythmias, particularly AF. Our research highlights the importance of routine screening and timely treatment of thyroid dysfunction to optimize the prevention and management of arrhythmias.