Glucose tolerance, insulin secretion, insulin sensitivity and glucose effectiveness in normal and overweight hyperthyroid women.

OBJECTIVE

Inter-relationships between insulin sensitivity and body weight in patients with hyperthyroidism remain incompletely understood. We have examined whether a mild excess of body weight exacerbates the metabolic abnormalities of spontaneous hyperthyroidism.

DESIGN AND PATIENTS

Insulin-modified intravenous glucose tolerance tests were performed on 14 hyperthyroid women with body mass indices (BMI) ranging from 21 to 31 kg/m2. A control group of 19 healthy women matched for age and BMI was also studied.

MEASUREMENTS

Intravenous glucose tolerance (KG), first and second-phase integrated insulin responses to glucose, the integrated glucose area under the curve (AUC), and minimal model parameters of insulin sensitivity (SI) and glucose effectiveness (SG) were determined.

RESULTS

Hyperthyroid women had mean KG, glucose-induced insulin secretion and SG values similar to those in control women. The mean glucose AUC was higher in hyperthyroid patients (P < 0.05). Lower insulin sensitivity was observed in hyperthyroid patients than in control women (SI = 0.38 +/- 0.07 vs 0.59 +/- 0.07 l/min pmol 10(4) (mean +/- SEM), P < 0.05). A steeper decline in insulin sensitivity with increase in body mass index was found in hyperthyroid women when compared with the control group, after adjusting for age. When groups were compared according to their BMI, hyperthyroid women with normal weight (BMI < or = 25 kg/m2, n = 8) had mean KG, insulin response to glucose, glucose AUC, SG and SI values similar to those in normal weight control women (n = 11). Overweight hyperthyroid patients (BMI > 25 kg/m2, n = 6) had a higher (P < 0.05) second-phase insulin response to glucose than normal weight patients, a higher glucose AUC (P < 0.05) than normal weight patients and overweight controls (n = 8), and a lower SI (P < 0.05) than normal weight patients and overweight controls. SG was not influenced by BMI in hyperthyroid patients.

CONCLUSIONS

These results suggest that overall glucose tolerance was not significantly affected in normal weight hyperthyroid women. However, when a moderate excess of weight is also present, a state of clear insulin resistance occurs.