Thyroid hormones have been proposed to have an influence on glucose metabolism. Although this mechanism has not been fully established, it has been proposed that thyroid hormones may influence β-cell mass, which is reduced in subjects with impaired fasting glucose and type 2 diabetes mellitus, and β-cell function. Studies in the past have reported that insulin secretion levels are increased in hyperthyroid subjects compared to euthyroid subjects. In euthyroid individuals there is scarce information on the role of thyroid hormones on insulin secretion. This was addressed in a study by Ortega et al., which measured the levels of thyroid stimulating hormones, free thyroxine, triiodothyronine, and plasma insulin levels in non-diabetic, euthyroid subjects.
The study used a subgroup of 55 healthy, euthyroid, adult members of the Gila River Indian Community near Phoenix, Arizona, USA. Levels of thyroid stimulating hormones, free thyroxine, triiodothyronine, and plasma insulin levels were measured in fasting plasma samples from subjects and in response to an intravenous glucose tolerance test and an oral glucose tolerance test, along with the percentage body fat using dual x-ray absorptiometry.
The results showed a positive association between free triiodothyronine concentration and fasting plasma insulin, acute insulin response, and incremental area under the curve of insulin in response to the intravenous and oral glucose tolerance tests, both before and after adjustment for age, sex, percentage body fat, glucose concentration, and insulin action.
The authors conclude that free triiodothyronine was independently associated with several measurements of insulin secretion in euthyroid individuals with normal glucose tolerance. Triiodothyronine concentrations are suggested to play a role in the regulation of insulin secretion.
Ortega, E., Koska, J., Pannacciulli, N., Bunt, J.C., Krakoff, J. European Journal of Endocrinology, 158, 217-221. DOI: 10.1530/EJE-07-0592
Journal paper