Five-year follow-up study on plasma insulin levels in newly diagnosed NIDDM patients and nondiabetic subjects.

A representative group of middle-aged (45- to 64-yr-old) patients with non-insulin-dependent diabetes mellitus (NIDDM) (n = 133; 70 men, 63 women) were examined at the time of diagnosis and 5 yr afterward for metabolic control and insulin response to oral glucose; 144 nondiabetic control subjects (62 men, 82 women) were similarly examined twice between 5-yr intervals. At the 5-yr examination, 56 of the diabetic patients (36 men, 20 women) were on diet therapy only, 60 (27 men, 33 women) received oral antidiabetic drugs, and 5 were treated with insulin. The metabolic control of diabetic patients was poor at the time of diagnosis and 5-yr examination. Fasting plasma insulin levels were higher in diabetic patients than in control subjects both at baseline (23 +/- 2 vs. 14 +/- 1 mU/L, P less than 0.01, for men; 26 +/- 2 vs. 15 +/- 1 mU/L, NS, for women) and 5-yr examination (19 +/- 1 vs. 16 +/- 2 mU/L, NS, for men; 29 +/- 5 vs. 15 +/- 1 mU/L, P less than 0.05, for women). The frequency of insulin deficiency in diabetic patients based on a postglucagon (1 mg i.v.) C-peptide level less than 0.60 nM was 3.3% at the 5-yr examination, indicating that true insulin deficiency was uncommon during the first years after diagnosis of diabetes in middle-aged subjects.