Abstract

HERRERA, JD; LEIVA, PL  and  MARTIN, ML. Insulin Resistance and Changes in thyrotropin levels in patients with euthyroidism or subclinic thyroid dysfunction. Rev. argent. endocrinol. metab. [online]. 2012, vol.49, n.4. ISSN 1851-3034.

Introduction: The association between alterations of the thyroid function and an increased risk of developing cardiovascular diseases has been established for several years. Strong published evidence supports the notion that clinical hypothyroidism increases the levels of LDL cholesterol, induces arterial hypertension, and increases the levels of homocystein. However, the relationship between all these well-known risk factors for coronary disease and subclinical thyroid dysfunction remains a controversial topic. In addition, the presence of Metabolic Syndrome, known as an association of cardiovascular risk factors including: central obesity, insulin resistance, dyslipidemia and arterial hypertension, increases the possibility of developing cardiovascular diseases, to such an extent that the main cause of death in patients with type 2 diabetes, who generally present all the aforementioned factors plus hyperglycemia, is myocardial infarction. Objective: The main objective of our study was to investigate the existence of an association between insulin resistance measured by HOMA-IR and TSH levels in euthyroid patients or subclinical thyroid dysfunction. Secondarily, we evaluated changes in the lipid profile of the groups studied. Methods: This was a retrospective study. We analyzed the levels of free T4, TSH, insulin, basal plasma glucose, total and HDL cholesterol, triglycerides and body mass index in 233 patients with euthyroidism or diagnosed with subclinical thyroid dysfunction. Patients were divided into three groups according to TSH levels: Group A (n = 31) with values of TSH less than 0.4 mIU/L; Group B (n = 136) with TSH between 0.4 and 2.5 mIU/L, and Group C (n = 66) with TSH above 2.5 mIU/L. Free T4, TSH and insulin were measured with immunochemiluminescence assays (Immulite 2000). Basal plasma glucose, total cholesterol, HDL cholesterol and triglycerides were measured with automated methods (Technicon/Bayer RA 1000 Chemistry Analyzer). All measurements were performed from the same blood sample, obtained early in the morning after a minimum fasting period of 12 hours. Results: We found that the levels of insulin and HOMA-IR in group B were significantly lower that in group C (7.91 ± 0.67 mIU/L vs. 10.23 ± 0.91 mIU/L - p = 0.0073 and 1.84 ± 0.17 vs. 2.49 ± 0.27 - p = 0.0113, respectively). This difference was independent of age and BMI. In addition, we observed a slight but significant decrease in HDL-cholesterol levels in group C as compared to group B (48.3 ± 0.5 vs. 46.3 ± 0.7 mg/dl; p = 0.0455) and an increase in triglycerides (146.9 ± 11.9 vs. 112.3 ± 5.6 mg/dl; p = 0.0162). The prevalence of insulin resistance defined as a value of HOMA-IR higher than 2.5 was greater in group C compared to B (39.5 % vs. 23.9 %; OR 2.06 - IC 95 %: 1.19-3.63 - p = 0.013). Finally, a weak but significant negative correlation was observed between HOMA-IR and free T4 (r - 0.22276; p = 0.0059) and a positive correlation was observed between HOMA-IR and TSH (r = 0.1909; p = 0.0066) in the whole cohort. Conclusions: We conclude that in the studied population, patients with TSH above 2.5 mIU/L vs. those with TSH between 0.4 and 2.5 mIU/L presented: 1) lower levels of HDL cholesterol, 2) higher levels of triglycerides, insulin and HOMA-IR, independently of age and BMI and, 3) a significant increase in the risk of having insulin resistance measured by HOMA-IR.

Keywords : Metabolic syndrome; Insulin resistance; Thyrotropin; Thyroid function.

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