Endocrine Abstracts

Introduction: Recent literature highlights the intricate link between thyroid function and atherosclerosis, particularly emphasizing its influence on carotid internal media thickness (cIMT). However, the studies yielded contradictory results, with some of them showing that subclinical hyper or hypothyroidism, may influence atherogenesis and increased cardiovascular risk, while others not showing such effect.

Objective: We aimed to investigate the association between thyroid function (TSH and FT4 quintiles) and incidence of increased carotid intima-media thickness (cIMT) in men and women, euthyroid or with subclinical conditions, from the ELSA-Brasil study.

Methods: This is a prospective cohort study using baseline and 8y-follow-up data of men (n= 2,057, 48.1±7.9 years old) and women (n = 2,857, 48.8±7.7 years old), without history of cardiovascular disease. Fasting serum TSH, FT4, and FT3 were determined (Roche Diagnostics) and quintiles were calculated. We included in the main analysis euthyroid participants (TSH 0.4-4.0 mIU/l and no use of levothyroxine and anti-thyroid medication), and participants with subclinical conditions (TSH any level and 0.93<FT4<1.70 ng/dL). Baseline levels of cIMT ≥ 0.68 (75th percentile) were classified as “increased cIMT”. Incidence of increased cIMT was defined as baseline cIMT<0.68 and follow-up CIMT≥0.68. We performed sex-stratified Cox regression models, univariate and adjusted (for age, race, BMI, smoking, diabetes, hypertension, dyslipidemia), to determine hazard ratio (HR) and 95% confidence intervals (CI). Sensitive analyses were done 1) excluding those who were taking medications that interfere on thyroid function; and 2) plus excluding participants with subclinical thyroid function.

Results: The incidence of increased cIMT was 26.0% (n = 535) for men and 21.5% (n = 614) for women. Men in the second quintile of FT3, compared to the third quintile, showed higher risk for incident cIMT in univariate (Hr = 1.51, CI=1.13-2.02, P = 0.005) and fully adjusted model (Hr = 1.49, CI=1.11-1.99, P = 0.007). For women, the lowest levels of TSH (Hr = 1.33, CI=1.03-1.72, P= 0.028) and FT3 (Hr = 1.26, CI=1.00-1.58, P = 0.046) were associated with cIMT incidence in the univariate after adjustment for confounder variables. No association was seen between FT4 titers and cIMT. Results remained the same in the sensitivity analyses, except for the association between FT3 and incident cIMT for euthyroid women.

Conclusions: Individuals, especially women, with lower levels of TSH and FT3 were associated with higher risk of developing increased cIMT. The findings may suggest an influence of thyroid function on the atherosclerotic process.