New data on the rate of progression of impaired glucose tolerance to NIDDM and predicting factors.

The Hoorn study has investigated the prevalence of impaired glucose tolerance (IGT) and diabetes in a random sample of the population, 50-75 years of age, in the small Dutch town of Hoorn. The percentage of the population identified as having IGT was 10.3%, while 8.4% had diabetes. The prevalence of both diabetes and IGT was higher in older subjects (70-74 years of age) than in younger subjects (50-54 years of age), suggesting that age is a major determinant of the prevalence of IGT and diabetes in a population. A prospective study of the development of non-insulin dependent diabetes mellitus (NIDDM) in the subjects identified as having IGT was then initiated. Preliminary results for the 158 subjects who have been followed for a mean of 2 years indicated that 28.5% (95% confidence interval, 15-42%) have progressed to NIDDM within this period. The progression rate calculated from this value is 13.8%/year (95% confidence interval, 3.5-24%/year). Analysis of possible determinants of conversion has revealed that 2-hour plasma glucose levels greater than 9.4 mmol/litre and increased fasting proinsulin levels are predictive of progression to NIDDM. This suggests that beta cell dysfunction, rather than increased insulin resistance, is responsible for the development of NIDDM.