The Relationship between Thyroid-Stimulating Hormone and Insulin Resistance in Incipient Elderly Type 2 Diabetics with Normal Thyroid Function

Abstract

Objective. To explore correlations between serum thyroid-stimulating hormone (TSH) concentration within the normal range and insulin resistance and its possible mechanism in incipient type 2 diabetes in elderly patients. Methods. 453 elderly patients with type 2 diabetes were divided into four groups by the quartile of TSH. Body mass index (BMI), waist-to-hip ratio (WHR), fasting plasma glucose (FPG), fasting insulin (FINS), homeostasis model assessment of insulin resistance (HOMA-IR) and homeostasis model assessment of insulin secretion (HOMA-β), blood lipids, and other indicators were compared among all groups, and correlation and regression analysis were conducted. 3T3-L1 preadipocytes were induced into mature adipocytes in vitro, and different concentrations of bovine TSH were used to stimulate adipocytes. The levels of TNF-α in the culture medium were detected by ELISA. Results. (1) With the increase of TSH, TC showed an increasing trend. Compared with the G1 group (4.80 ± 1.08), G2 group (5.13 ± 1.16), G3 group (5.14 ± 1.39), and G4 group (5.38 ± 1.16), the difference was statistically significant ( $P<0.05$ or $P<0.01$ ). The LDL also showed an increasing trend. Compared with the G4 group (3.47 ± 0.89), the G1 (3.12 ± 0.82) and G2 groups (3.14 ± 1.05) had a lower LDL, and the difference was statistically significant ( $P<0.01$ ). The BMI increased between the G4 group (26.7 ± 3.97) and the G1 group (25.6 ± 3.54), and the difference was statistically significant ( $P<0.05$ ). (2) The serum TSH level was positively correlated with FPG, FINS, HOMA-IR, TC, and LDL (R = 0.292, 0.271, 0.394, 0.195, and 0.178, all $P<0.01$ ). (3) TSH is the dependent variable, other indicators are independent variables, and multiple stepwise regression analysis is performed; the results show that only HOMA-IR, TC, and LDL enter the regression equation. (4) The TSH stimulated TNF-α secretion of 3T3-L1 adipocytes in a dose-dependent manner. Conclusion. The TSH level was positively correlated with the insulin resistance and LDL in the elderly incipient type 2 diabetic patients. Higher levels of TSH may be involved in the development of insulin resistance in the elderly incipient type 2 diabetic patients.