Objective: Although clinical hyperthyroidism (HR) is associated with insulin resistance, the information on insulin action in subclinical hyperthyroidism (SHR) is limited. Design and methods: To investigate this, we assessed the sensitivity of glucose metabolism to insulin in vivo (by an oral glucose tolerance test) and in vitro (by measuring insulin-stimulated rates of glucose transport in isolated monocytes) in 12 euthyroid subjects (EU), 16 patients with HR, and 10 patients with SHR. Results: HR and SHR patients displayed higher postprandial glucose levels (area under the curve, AUC0–300 32 190G1067 and 31 497G716 mg/dl min respectively) versus EU (27 119 G1156 mg/dl min, P!0.05). HR but not SHR patients displayed higher postprandial insulin levels (AUC0–300 11 020G985 and 9565G904 mU/l min respectively) compared with EU subjects (AUC0–300 7588G743 mU/l min, P!0.05). Homeostasis model assessment index was increased in HR and SHR patients (2.81G0.3 and 2.43G0.38 respectively) compared with EU subjects (1.27 G0.16, P!0.05), while Matsuda and Belfiore indices were decreased in HR (4.21G0.41 and 0.77G0.05 respectively, P!0.001) and SHR patients (4.47G0.33 and 0.85G0.05 respectively, P!0.05 versus EU (7.76G0.87 and 1 respectively). At 100 mU/ml insulin, i) GLUT3 levels on the monocyte plasma membrane were increased in HR (468.8G7 mean fluorescence intensity (MFI)) and SHR patients (522.2G25 MFI) compared with EU subjects (407G18 MFI, P!0.01 and P!0.05 respectively), ii) glucose transport rates in monocytes (increases from baseline) were decreased in HR patients (37.8G5%) versus EU subjects (61.26G10%, P!0.05). Conclusions: Insulin-stimulated glucose transport in isolated monocytes of patients with HR was decreased compared with EU subjects. Insulin resistance was comparable in patients with both HR and SHR.

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Studies of insulin resistance in patients with clinical and subclinical hypothyroidism.

To explore the relationship between serum thyrotropin and components of metabolic syndrome in a Chinese cohort. A total of 1534 adult inhabitants in DaDong district of Shenyang were asked to fulfill the questionnaire, complete physical examination and OGTT. Blood samples were collected to test thyrotropin (TSH), fasting plasma glucose (FPG), OGTT 2h PG, fasting insulin (FINS), triglyceride (TG) and high density lipoprotein cholesterol (HDL-C). Serum TSH in metabolic syndrome group was higher than that in the non-metabolic syndrome group (2.54 mIU/L vs. 2.22 mIU/L, p<0.05). TG level increased significantly in subclinical hypothyroid group compared with euthyroid subjects (1.73±0.12 mmol/L vs. 1.47±0.03 mmol/L, p<0.05), and HDL-C decreased significantly in patients with subclinical hypothyroidism compared with euthyroid subjects (1.26±0.27 mmol/L vs. 1.33±0.27 mmol/L, p<0.05). The prevalence of hypertension was higher in the subclinical hypothyroid group than that in euthyroid group (42.86% vs. 33.2%, p<0.05). The serum TSH within the reference range was positively related with the prevalence of overweight/obesity. Slight increase in serum TSH maybe a risk factor for metabolic syndrome.

The relationship between serum thyrotropin and components of metabolic syndrome.

Evidence for a relationship between T4 and T3 and glucose metabolism appeared over 100 years ago when the influence of thyroid hormone excess in the deterioration of glucose metabolism was first noticed. Since then, it has been known that hyperthyroidism is associated with insulin resistance. More recently, hypothyroidism has also been linked to decreased insulin sensitivity. The explanation to this apparent paradox may lie in the differential effects of thyroid hormones at the liver and peripheral tissues level. The purpose of this paper is to explore the effects of thyroid hormones in glucose metabolism and analyze the mechanisms whereby alterations of thyroid hormones lead to insulin resistance.

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Why can insulin resistance be a natural consequence of thyroid dysfunction

Subclinical hypothyroidism (sH) has been associated with atherosclerotic cardiovascular disease even in the absence of hypercholesterolemia. Objective: Our study was designed to assess the hypothes...

Lipoprotein Alterations, Hepatic Lipase Activity, and Insulin Sensitivity in Subclinical Hypothyroidism: Response to L-T4 Treatment

Insulin resistance is defined as a glucose homeostasis disorder involving a decreased sensitivity of muscles, adipose tissue, liver and other body tissues to insulin, despite its normal or increased concentration in blood. Insulin resistance may be asymptomatic or occur presenting a variety of disorders, such as: glucose tolerance impairment, type 2 diabetes, as well as hypercholesterolaemia, hypertriglyceridaemia, obesity, and arterial hypertension. Insulin acts via specific receptors present on the surface of most cells of the body. The greatest number of these receptors is found on adipocytes, hepatocytes and striated muscle cells. There are three mechanisms of insulin resistance: pre-receptor, receptor and post-receptor. Multiple methods of assessing insulin resistance are based on the concurrent measurements of glucose and insulin levels in blood serum. The glucose and insulin measurements are conducted in baseline conditions or after intravenous administration of a specific quantity of glucose or insulin. The methods of assessing insulin resistance are divided into direct and indirect. The current 'gold standard' in the assessment of insulin sensitivity is the determination of tissue glucose utilisation using the metabolic clamp technique. The presence of disorders of carbohydrate metabolism has been demonstrated in thyroid disease involving either overt hyperthyroidism or overt hypothyroidism. The severity of the disease is proportional to the severity of these disorders. The possible influence of subclinical forms of both hyperthyroidism and hypothyroidism on carbohydrate disorders is still under discussion. Thyroid hormones have a significant effect on glucose metabolism and the development of insulin resistance. In hyperthyroidism, impaired glucose tolerance may be the result of mainly hepatic insulin resistance, whereas in hypothyroidism the available data suggests that the insulin resistance of peripheral tissues prevails.

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Insulin resistance and thyroid disorders.

Subclinical hypothyroidism (SH), defined as an asymptomatic state characterized by normal serum concentrations of free thyroxine and elevated serum concentrations of TSH. The aim of this study is to investigate the complex interplay between insulin resistance and low grade chronic inflammation in Kuwaiti women with subclinical hypothyroidism. Thirty four women with subclinical hypothyroidism (SH) and 20 healthy women as controls matched to the patient group for sex, age and body mass index (BMI), were enrolled in this prospective study. TSH, FT4, C reactive protein, glucose, insulin, Homeostasis Model assessment (HOMA), total cholesterol (TC), triglycerides (TG), low-density lipoprotein cholesterol (LDL-C), high-density lipoprotein cholesterol (HDL-C) were estimated. Total cholesterol and LDL-C were significantly higher in patients with SCH as compared with control subjects, however triglyceride and HDL-C were not statistically different. CRP was not statistically different between the SCH patients and control group (3.64 ± 0.94 Vs 3.18 ± 0.71 P>0.05). Insulin levels were significantly higher in the SCH group comparable to the control (12.5 ± 2.67 Vs 10.80 ± 2.01 p 0.05). Patients with subclinical hypothyroidism exhibited elevated atherogenic parameters (hyperinsulinemia, total cholesterol, LDL-C). Therefore screening and treatment for subclinical hypothyroidism may be warranted due to its adverse effects on lipid metabolism.

Eid Alfadhli

Papers

Subclinical hypothyroidism is associated with early insulin resistance in Kuwaiti women.