Objective: Apart from the effects of a dysfunctional thyroid gland on the cardiovascular system, thyroid function within the reference range may have an impact on the vasculature. The present study aimed to evaluate the association between thyroid function and markers of arterial structure and function in euthyroid postmenopausal women.
Methods: The present cross-sectional study recruited 106 healthy postmenopausal women with a mean age of 55.0 years and thyroid-stimulating hormone (TSH) levels within the laboratory reference range (0.4-4.5 μIU/ml). Anthropometric and biochemical measures as well as blood pressure were determined in each individual. Vascular structure and function were assessed by intima-media thickness, pulse wave velocity (PWV), augmentation index and flow-mediated dilation, respectively. We evaluated the associations between arterial markers and serum TSH, free triiodothyronine, free thyroxin, as well as serum thyroid peroxidase and thyroglobulin autoantibodies.
Results: Mean levels of PWV increased linearly across increasing TSH quartiles (P value = 0.014). Individuals with serum TSH greater than 2.5 μIU/ml had significantly higher values of PWV when compared with individuals with TSH levels below 2.5 μIU/ml (9.68 ± 1.97 vs. 8.54 ± 1.83 m/s; P = 0.030). In multivariate analysis, age, insulin resistance and TSH above 2.5 μIU/ml were the only significant predictors of PWV (TSH, β-coefficient = 0.222; P = 0.014). No associations were found between the remaining markers and levels of thyroid hormones, whereas thyroid antibodies were not associated with any of the arterial markers.
Conclusion: Women with TSH levels in the upper reference range have increased arterial stiffness compared to women with lower TSH. The upper limit of normal TSH in postmenopausal women may need re-evaluation with respect to the effects on the vasculature.