Thyroid function, glycemic control, and diabetic nephropathy in patients with type 2 diabetes over 24 months: prospective observational study

Background The higher prevalence of thyroid dysfunction in type 1 diabetes patients has been well established, whereas it is a matter of debate whether that is also observed in type 2 diabetes patients.

This study was conducted to reveal whether higher prevalence of thyroid dysfunction is observed in patients with type 2 diabetes.

Methods We examined thyroid functions and thyroid autoantibodies in 200 patients with type 2 diabetes and 225 controls, with 24 months follow up for those with type 2 diabetes.

Results Serum free triiodothyronine (fT3) levels and fT3/free thyroxine (fT4) ratio were significantly lower, while fT4 levels were significantly higher in patients with type 2 diabetes.

The number of patients with thyroid dysfunction or patients positive for thyroid autoantibodies were not different between the two groups.

The fT3/fT4 ratio was positively and negatively correlated with serum c-peptide and HbA1c levels, respectively, suggesting that the difference can be attributable to insulin resistance and diabetic control.

In the follow-up observation, we found no significant correlation between basal thyrotropin (TSH), fT3, fT4 or fT3/fT4 ratio with the amounts of changes of HbA1c levels at 12 or 24 months after the basal measurements.

There was a negative relationship between TSH levels and eGFR at baseline measurements, but TSH levels did not seem to predict future decline of eGFR levels.

No relationship was observed between urine albumin/ g‧cre levels and thyroid function.

Conclusion Thyroid dysfunction and thyroid autoantibodies were not different in prevalence between patients with type 2 diabetes and controls, although in patients with type 2 diabetes, the fT3/fT4 ratio was decreased.

Basal thyroid function did not predict future diabetes control or renal function within 24 months of follow-up.