Circulating IGF-I concentrations are low and not correlated to glycaemic control in adults with type 1 diabetes

Objective: To study plasma concentrations of insulin-like growth factor-I (IGF-I) in adults with type 1 diabetes (IDDM) in comparison with a reference population, and the influence of glycaemic control, dose of insulin, and sex on the concentration of circulating IGF-I in IDDM, Design and methods: Patients with type 1 diabetes were recruited consecutively from our outpatient diabetes unit. In all, 79 men and 55 women aged 20-60 years with a disease duration greater than or equal to 6 years (range 6-51 years) took part in the study. A reference population of 80 men and 83 women aged 20-60 years was randomly obtained from the population registry. IGF-I was measured with radioimmunoassay after acid-ethanol extraction. Results: Mean +/- S.D. values of IGF-I were lower in patients with diabetes (146+/-66 mu g/l) than in controls (238+/-83 mu g/l, P<0.001). Those with diabetes had lower IGF-I concentrations in all age groups and the differences were highly significant in all decades except in women aged 50-59 years, IGF-I was negatively correlated with age in patients and controls. No correlation was found between IGF-I and glycaemic control measured as haemoglobin A(1c) (HbA(1c)) in the patients, IGF-I was positively associated with the dose of insulin/kg body weight in male patients independently of age, HbA(1c) and body mass index (P<0.03), but not in female patients (P=0.14). Conclusions: Our data show that IGF-I concentrations are low in adult patients with type 1 diabetes with a disease duration greater than or equal to 6 years, independently of glycaemic control. This suggests that subcutaneous insulin substitution is inadequate to normalize circulating IGF-I concentrations in patients without endogenous insulin secretion.