Higher Serum Free Triiodothyronine Levels within the Normal Range Are Associated with Metabolic Syndrome Components in Type 2 Diabetic Subjects with Euthyroidism

Abstract

Associations of thyroid hormones with visceral obesity and insulin resistance in obese subjects with euthyroidism have been reported. However, there are no such reports in subjects with type 2 diabetes. The purpose of our study is to observe a relationship between thyroid hormones and components of metabolic syndrome (MetS) in type 2 diabetic subjects with euthyroidism defined by normal thyroid stimulating hormone (TSH) and free thyroxine (FT4) levels. Subjects were 301 Japanese patients with type 2 diabetes. Serum TSH, FT4, free triiodothyronine (FT3), and variables related to MetS were measured. MetS was defined by the Japanese criteria and the criteria of the National Cholesterol Education Program modified for Asians. We found that serum FT3 levels were significantly and positively associated with BMI, visceral fat area, systolic and diastolic blood pressure, estimated glomerular filtration rate, serum triglyceride, and urine C peptide as a marker of insulin production, whereas negatively with age and HbA1c. In contrast, fewer numbers of variables were associated with serum TSH and FT4 levels. By a multiple regression analysis, FT3 level was independently associated with components of MetS such as visceral fat area, systolic blood pressure, and fasting blood glucose levels. On the other hand, the presence of these MetS components was independently associated with FT3 levels and urine C peptide. In conclusion, these results suggest a significant relationship between serum FT3 levels and components of MetS in type 2 diabetic subjects with euthyroidism, and imply a role of FT3 in MetS in type 2 diabetes.

Association between the serum concentration of triiodothyronine with components of metabolic syndrome, cardiovascular risk, and diet in euthyroid post-menopausal women without and with metabolic syndrome

“…In agreement with our results, a high T3 (total or free) concentration has been associated with a high BMI (De Pergola et al 2010; Taneichi et al 2011; Tarcin et al 2012; Roef et al 2014), which may be related to the promotion of adipocyte differentiation (Flores-Delgado et al 1987). Triiodotironine also shows a positive association with insulin resistance (Lambadiari et al 2011; Tarcin et al 2012) but a negative association with hyperglycemia (Taneichi et al 2011). This fact could be explained because the T3 affects the absorption of glucose in the gastrointestinal tract, the liberation of glucose by hepatic tissue, cellular glucose transport, insulin secretion by pancreas, and the glucose utilization by muscle cells (Wang 2013).…”

“…There is much information about the relation between T4 or TSH and cardio-metabolic variables (De Pergola et al 2010; Lambadiari et al 2011; Taneichi et al 2011; Tarcin et al 2012), but only a few studies have been done in old people, and particularly in post-menopausal women (Park et al 2009; Takamura et al 2009; Topsakal et al 2012). In agreement with our results, a high T3 (total or free) concentration has been associated with a high BMI (De Pergola et al 2010; Taneichi et al 2011; Tarcin et al 2012; Roef et al 2014), which may be related to the promotion of adipocyte differentiation (Flores-Delgado et al 1987).…”

“…Some studies have found that the relationship between thyroid hormones and cardio-metabolic variables may be intensified in patients with diabetes, obesity, or MetS (De Pergola et al 2010; Lambadiari et al 2011; Taneichi et al 2011; Tarcin et al 2012; Topsakal et al 2012), suggesting that the onset of these pathologies could affect the thyroid function. In agreement, it has been suggested that obese people with a normal thyroid gland may have a hyperactivated hypothalamic-pituitary-thyroid axis, increasing the concentration of TSH and thyroid hormones (Laurberg et al 2012).…”

Thyroid Disorders in Patients of Type 2 Diabetes Mellitus

“…This may be related to an association between higher FT3 levels, and decreased HbA1c i.e. low total T3 [22,23].…”

Free Triiodothyronine and Cholesterol Levels in Euthyroid Elderly T2DM Patients

“…Based on the considerations mentioned above, the relationship between thyroid function and the metabolic syndrome (MetS) has become a subject of interest for many research groups during the last few years [14], leading to the conclusion that even low-normal T 4 levels may contribute to increased cardiovascular risk associated with lipoid abnormalities in people with the MetS [15]. Some of these studies reported that T 3 behaved in a different way, being positively associated with body mass index (BMI) and waist girth [16–18].…”