Metabolic evolution of type 2 diabetes: a 10-year follow-up from the time of diagnosis.

Objectives: To investigate fasting and post-load plasma glucose, insulin and C-peptide levels during oral glucose tolerance tests in patients with type 2 diabetes and in control subjects, and the metabolic evolution of the diabetes.

Design, Setting And Subjects: A 10-year prospective study consisting of a representative group of 133 (70 men, 63 women) newly diagnosed type 2 diabetic patients diagnosed at health centres between 1979 and 1981 and 144 (62 men, 82 women) nondiabetic control subjects recruited from the population register. At baseline, diabetic subjects were treated with diet only. The subjects were studied at baseline and after 5 and 10 years.

Main Outcome Measures: The changes in plasma glucose, insulin and C-peptide levels in diabetic and control subjects at baseline and after 5 and 10 years follow-up. Factors associated with the decline in insulin and C-peptide levels in diabetic patients (e.g. metabolic control, islet cell antibodies).

Results: A slight increase in glucose levels was seen during the follow-up in both diabetic with diet and/or oral drug treated patients, but post-glucose insulin (and C-peptide and 5- and 10-year examination) levels declined in diabetic patients; this was opposite to the controls, in whom the levels tended to increase. The decline in insulin levels (area under the curve) during the follow-up was greatest in those diabetic patients with poor metabolic control during the follow-up. The cumulative incidence of requirement for insulin based on various cut-off levels for post-glucagon C-peptide nearly doubled between the 5- and 10-year examinations. Islet cell antibodies were predictive of insulin deficiency.

Conclusions: Type 2 diabetes was characterized by progressive impairment of insulin response to glucose and this decline was associated with poor metabolic control of diabetes.