Correlation between different degree and duration of metabolic control and thyroid hormone levels in type 1 and type 2 diabetics.

Thyroxine (T4), triiodothyronine (T3), reverse T3 (rT3) and HbA1c were assayed in 21 insulin-dependent (type 1) diabetics and in 45 non-insulin-dependent (type 2) diabetics with normal thyroid function and different levels of control, and were compared to values found in apparently healthy controls. rT3 and rT3/T3 ratio were significantly increased both in type 1 and type 2 diabetics. T3 and T4 were significantly lower in type 2 diabetics than in the controls. Significant positive correlations of HbA1c to rT3 (r = 0.63) and to rT3/T3 ratio (r = 0.53) were found in type 1, and in type 2 diabetics (HbA1c, rT3-r = 0.50), (HbA1c, rT3/T3-r = 0.37). There was no correlation between glycemia (BG), relative body weight (RBW) and thyroid hormones. These data suggest that the alterations of thyroid hormones in type 1 and type 2 diabetes mellitus reflect the degree of control better than the hyperglycemia and the duration of metabolic unbalance.