Association Between Changes in Thyroid Hormones and Incident Type 2 Diabetes: A Seven-Year Longitudinal Study

Area of Science:

• Endocrinology
• Metabolic Diseases
• Clinical Research

Background:

• Thyroid hormones play a crucial role in regulating glucose metabolism.
• The relationship between normal-range thyroid hormones and type 2 diabetes mellitus (T2DM) is not fully understood.
• Euthyroid subjects, those with normal thyroid function, are the focus of this investigation.

Purpose of the Study:

• To investigate the association between baseline levels and changes in thyrotropin (TSH), free thyroxine (FT4), and triiodothyronine (TT3) and the incidence of T2DM in euthyroid individuals.
• To determine if thyroid hormone fluctuations within the reference range impact T2DM risk.

Main Methods:

• A cohort of 6235 euthyroid subjects without T2DM was followed from 2006-2012.
• Thyroid function tests (TSH, FT4, TT3) were assessed at baseline and at follow-up.
• Changes in hormone levels were calculated, and Cox proportional hazards models were used to analyze T2DM incidence, adjusting for confounders.

Main Results:

• An increasing TSH level change was associated with a higher risk of incident T2DM (HR=1.44).
• Increasing changes in triiodothyronine (HR=0.60) and free thyroxine (HR=0.34) showed protective effects against T2DM.
• These associations remained significant even when hormones were analyzed continuously, but baseline levels were not associated with diabetes risk.

Conclusions:

• Individual changes in TSH and thyroid hormones, even within the normal reference range, represent an additional risk factor for incident T2DM.
• Monitoring thyroid hormone dynamics may offer insights into T2DM risk stratification.