Effect of diabetic control on the level of circulating thyroid hormones

Abstract

Basal plasma levels of thyroxine (T4), triiodothyronine (T3) and reverse T3 were determined by radioimmunoassay in 44 control subjects, 44 Type 1 (insulin-dependent) and 39 Type 2 (non insulin-dependent) diabetic patients aged from 15 to 75 years. All were clinically euthyroid. The quality of diabetic control was assessed by the percentage of glycosylated haemoglobin. In both the diabetic groups there was a significant decrease in T3 and a rise in reverse T3 whereas T4 was normal. We found no significant differences between plasma thyroid hormone levels in Type 1 and Type 2 diabetic patients. In the poorly controlled diabetics (glycosylated haemoglobin greater than or equal to 12%), T3 was 90 +/- 5 ng/dl, which differed significantly from the level found in the better controlled patients (106 +/- 5 ng/dl, p less than 0.01). In the diabetic patients without associated illness, a negative linear correlation was found between T3 and glycosylated haemoglobin and a positive correlation between reverse T3/T3 and glycosylated haemoglobin. No correlation between T3 or reverse T3 and fasting blood glucose could be established. In conclusion, many diabetics showed a low T3 syndrome suggesting that there may be an impairment in the extrathyroidal conversion of T4 to T3. This may well be enhanced by a poor diabetic control (glycosylated haemoglobin greater than or equal to 12%).

Thyroid Disorders in Patients of Type 2 Diabetes Mellitus

“…TRH synthesis decreases in diabetes mellitus and also there is loss of nocturnal TSH peak which is responsible for the occurrences of low thyroid hormone levels in some diabetics. In euthyroid individuals with diabetes mellitus, the serum T3 levels, basal TSH levels and TSH response to thyrotropin releasing hormone (TRH) all are strongly influenced by the glycemic status [17,18]. The levels of TSH in our study were not clinically significant in diabetics as compared to non diabetics.…”

“…Thyroid hormone replacement is associated with a decrease in HbA1c level, which is influenced by increased erythropoiesis rather than by changes in glucose level. The observation of negative correlation between T3 and HbA1c is supported by the views of various authors [17,20,21] who state a derangement of glycemic control in type 2 diabetes which influences the thyroid hormone levels. Furthermore, significant negative correlations were noted between parameters of glycemic control and serum T3 levels respectively.…”

“…A ''Low T3 state'' is described as low serum total and free T3 levels but near normal serum T4 and TSH concentrations [16]. Low serum T3 is due to reduced peripheral conversion of T4 to T3 via 5 0 monodeiodination reaction [17]. It is known that insulin, an anabolic hormone enhances the levels of FT4 while it suppresses the levels of T3 by inhibiting hepatic conversion of T4-T3 [13].…”

Serum TSH, T₄, T₃, FT₄, FT₃, rT₃, and TBG in Youngsters with Non-Ketotic Insulin-Dependent Diabetes mellitus

“…In fact, low levels of triiodothyronine (T3) have been observed in diabetic patients with keto acidosis [1][2][3] as well as in severely [4] and long-term hyperglycaemic diabetics [5]. Low levels of thyroxine (T4) have been reported in ketotic diabetics [6] but rarely in non-ketotic ones [5,7,8].…”

Relation between diabetes mellitus, thyroid hormones and caffeine

“…In DM condition, different investigations show that the serum levels influence in the control of diabetic condition and suggest a relation between the decrease of T 3 production and the worsening of glucose utilization (Schlienger et al, 1982). Furthermore, thyrotoxicosis causes hyperinsulinemia with TH reduction and an increased glucose synthesis, what, by unknown mechanisms, triggers IR (Aguayo- Mazzucato et al, 2013).…”