Thyroid function, serum lipids and insulin resistance in patients with autoimmune thyroiditis
Celestino Neves1, Marta Alves1, Luís Miguel Pereira1, Isolina Pimentel1, Ema Carvalho1, Renata Carvalho2, Cristina Guimarães2, João Pedro Ramos2, Davide Carvalho1, José Luís Delgado2 & José Luís Medina1
Objective: The aim of this study was to examine the hypothesis that thyroid function, in euthyroid subjects with autoimmune thyroiditis (AIT), is associated with insulin resistance, serum lipid concentrations, and other cardiovascular (CV) risk factors. Subjects and Methods: We recorded thyroid function tests, BMI, insulin resistance markers comprising the Homeostasis Model Assessment for insulin resistance (HOMA-IR), the Quantitative Insulin Sensitivity Check Index (QUICKI), HISI (Hepatic Insulin Sensitivity Index), WBISI (Whole-Body Insulin Sensitivity Index), IGI (Insulinogenic Index) and the levels of total cholesterol (TC), HDL, LDL-cholesterol, triglycerides (TG), apolipoprotein B (ApoB), ApoA1, lipoprotein(a) (Lp[a]), homocysteine, CRP (C-reactive protein), folic acid and vitamin B12 levels, in 250 patients with AIT. A 75-g OGTT was performed in the morning (before 11 AM), and blood samples were obtained every 30 min for 120 min for measurements of plasma glucose, insulin, and C-peptide. Statistical analysis was performed with ANOVA and Pearsons correlations test. Results are expressed as means S.D. or percentages. A two-tailed P value <0.05 was considered significant.
Results: There were significant positive correlations between TSH and serum total cholesterol (r=0.382, P=0.01), LDL (R=0.384; P=0.01), TG (R=0.278; P=0.01), and ApoB (R=0.341; P=0.01). BMI was positively associated with FT4 (R=0.274; P=0.01) and negatively associated with HDL (R=−0.279; P=0.01) and Apo A1 (R=−0.299; P=0.01). There were significant negative correlations between CRP and HDL(R=−0.269; P=0.01) and a significant positive correlation between CRP and TG (R=0.567; P=0.01), and homocysteine (R=0.234; P=0.05). There were significant positive correlations between IGI and TG (R=0.264; P=0.01) and TSH (R=0.217; P=0.05), and between WBISI and HDL-C (R=0.203; P=0.05).
Conclusion: Thyroid function and lipid levels are associated even in subjects classified as being euthyroid, thereby extending the established relation between (sub)clinical hypothyroidism and hyperlipidemia in the normal range. These findings are consistent with an increased cardiovascular risk in subjects with low normal thyroid function.