Inverse Correlation between Free Triiodothyronine to Free Thyroxine Ratio and Dietary Sodium Intake in Patients with Type 2 Diabetes Taking Dipeptidyl Peptidase 4 Inhibitors: A Retrospective Cohort Study

Abstract

Objective: This clinical study investigated the hypothesis that patients with type 2 diabetes, who consume more dietary sodium while taking dipeptidyl peptidase 4 inhibitors (DPP4is), would demonstrate increased iodothyronine deiodinase-2 activity, elevating the free triiodothyronine to free thyroxine ratio. Materials and methods: This study included 157 patients with type 2 diabetes mellitus. Dietary salt intake was estimated following Tanaka’s formula. Pearson’s correlation coefficients were calculated to estimate the linear correlations between variables. Results: The DPP4i and non-DPP4i groups included 58 (female/male = 15/43) and 99 participants (female/male = 37/62), respectively. The patient characteristics of the DPP4i versus non-DPP4i groups were as follows: mean age (years): 70.2 ± 10.7 versus 68.3 ± 11.7; mean type 2 diabetes duration (years):16.8 ± 10.9 versus 16.5 ± 12.7; mean thyroid-stimulating hormone (μU/mL): 2.04 ± 1.75 versus 2.036 ± 1.381; mean free triiodothyronine (FT3) (pg/mL): 2.792 ± 0.378 versus 2.741 ± 0.402; free thyroxine (FT4) (ng/dL): 1.08 ± 0.216 versus 1.134 ± 0.237; FT3/FT4 ratio: 2.569 ± 0.487 versus 2.486 ± 0.486; sodium intake (g/day): 10.4 ± 2.911 versus 10.41 ± 2.671. The free triiodothyronine to free thyroxine ratio was inversely correlated with dietary sodium intake in the DPP4i group (r = −0.444) but demonstrated no correlation with dietary sodium intake in the non-DPP4i group (r = −0.153). Conclusions: The results are different from those of mouse adipose tissue, but DPP4is may affect iodothyronine deiodinase-2 activity in patients with type 2 diabetes under certain conditions. Clinicians should pay close attention to DPP4i intake and dietary sodium consumption when estimating the iodothyronine deiodinase activity of patients with type 2 diabetes.