Higher Parametric Thyroid Feedback Quantile-based Index Is a Predictor of Type 2 Diabetes in a German Population Sample.

Context: Type 2 diabetes has been described to be associated with hypothyroidism but we recently found that a decrease in pituitary sensitivity to thyroid hormone is associated with diabetes, obesity, and metabolic syndrome.

Objective: We aimed to assess the longitudinal nature of this association in the population-based Study of Health in Pomerania (SHIP) in Germany.

Methods: Among a population-based sample of 4308 participants aged 20 to 79 years, 77% were followed for a period of 5 years. We studied 2542 participants without diabetes or thyroid medication at baseline and complete data in the variables of interest. Data of baseline free thyroxine (fT4) and thyrotropin (TSH) were used to calculate the Parametric Thyroid Feedback Quantile-based Index (PTFQI), which measures whether TSH remains elevated despite fT4 being high. It uses the average population response as reference. PTFQI association with incidence of type 2 diabetes over 5 years was estimated with Poisson regression models adjusted for age, sex, and body mass index (BMI).

Results: Compared with the first PTFQI quartile, incidence rate ratios for diabetes were 1.54 (95% CI, 0.97-2.46), 1.55 (0.94-2.57), and 1.97 (1.27-3.10) for the upper quartiles (P trend = .004) after adjusting for age and sex. The association remained statistically significant after additionally adjusting for BMI: 1.64 (1.05-2.59) for the fourth vs the first quartile (P trend = .043).

Conclusion: An elevation of the pituitary TSH-inhibition threshold is associated with incident type 2 diabetes independently of BMI. The PTFQI might have clinical potential for prognosis and metabolic status monitoring.