Non-insulin dependent diabetic patients have a progressively reduced insulin secretion in relation to the increased disease duration

Conflicting results have been reported on the possibility that a progressive deterioration of β-cell function occurs in patients with non-insulin dependent diabetes mellitus (NIDDM). This paper reports a cross sectional study of C-peptide plasma levels after i.v. glucagon administration in 152 NIDDM patients. C-peptide values were negatively correlated (p <0.001) with the duration of diabetes both in obese and non-obese patients. Moreover, when the 152 patients were subdivided into 4 quartiles (from quartile 1 to 4 depending on the increasing duration of diabetes), a significant (p <0.001) and progressive decrease of C-peptide values was observed, with the highest values into quartile 1 and the lowest values into quartile 4. Finally, in a small group of 10 NIDDM patients, a longitudinal investigation was carried out by repeating C-peptide measurements 2 years after the first determination. Although the short term follow up period (only 2 years), C-peptide values were significantly lower (p <0.05) at the second determination. The observed decrease of C-peptide values was independent of changes in fasting plasma glucose, body weight and antidiabetic treatment. All together these data support the possibility that in both obese and non-obese NIDDM patients a progressive deterioration of β-cell secretory capacity takes place with increasing disease duration.