Higher serum free thyroxine levels are associated with coronary artery disease

Thyroid hormone has many effects on the heart and cardiovascular system. Thyrotoxicosis is associated with increased cardiovascular morbidity and mortality, primarily due to heart failure and thromboembolism. However, the relationship between thyroid hormone excess and the cardiac complications of angina pectoris and myocardial infarction remains largely speculative. Moreover, few studies have been reported on the effect of thyroid hormone levels within normal range on coronary artery disease (CAD). Therefore we examined the association of thyroid function with coronary artery diseases in euthyroid angina patients. Total 192 subjects (mean age; 60.8 yrs) were enrolled in which coronary angiograms were performed due to chest pain. We measured free thyroxine (FT₄), thyroid stimulating hormone (TSH), serum lipid levels and high-sensitivity C-reactive protein (hsCRP) levels and analyzed their association with the presence of CAD. Serum FT₄ levels were higher in patients with CAD compared with the patients without CAD (1.31 ± 0.30 vs 1.20 ± 0.23, p = 0.006), and high FT₄ level was associated with the presence of multi-vessel disease. Multivariate analysis showed that age (odds ratio (OR) 1.04; 95% confidence interval (CI) 1.01-1.07, p = 0.007), hypertension (OR 2.04; 95% CI 1.06-3.90, p = 0.036) and FT₄ (OR 4.23; 95% CI 1.12-15.99, p = 0.033), were the determinants for CAD. The relative risk (RR) for CAD in highest tertile of FT₄ showed increased risk compared with the lowest tertile (RR 1.98; 95% CI 0.98-3.99, p<0.001). Our study showed that FT₄ levels were associated with the presence and the severity of CAD. Also, this study suggests that elevated serum FT ₄ levels even within normal range could be a risk factor for CAD. Further studies will be necessary to confirm the relationship of thyroid function and CAD.