The natural history of impaired glucose tolerance in the Micronesian population of Nauru: A six-year follow-up study

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Abstract
A longitudinal study of 266 randomly selected non-diabetic Nauruans (215 normal subjects, 51 with impaired glucose tolerance) has permitted the natural history of impaired glucose tolerance to be studied in this Micronesian population. Nauruans are known to suffer from a very high prevalence of abnormal glucose tolerance. The subjects were first examined in 1975–1976, and a follow-up examination was performed in 1982. Of the subjects with impaired glucose tolerance, 26% developed diabetes during the study period (4% per annum) compared with 7% of normal subjects (1% per annum). After controlling for the effects of both age and obesity, the risk of subsequent diabetes for subjects with impaired glucose tolerance remained significantly higher than for normal subjects (odds ratio 3.6, 95% confidence interval 1.4–9.1). Of those with impaired glucose tolerance on initial examination, 39% were normoglycaemic at follow-up. In subjects with impaired glucose tolerance, of nine factors examined only plasma glucose concentration at the time of the initial examination was consistent in predicting progression to diabetes, when the data were examined by both univariate and multivariate methods. Both 2-h and fasting plasma glucose values were useful predictors. Thus, Nauruans with impaired glucose tolerance have a higher risk of subsequent diabetes than their normoglycaemic counterparts, after controlling for age and obesity. Nevertheless, the prognosis of impaired glucose tolerance is unpredictable as a substantial proportion of such subjects return to normality. Plasma glucose concentration is the most important predictor of subsequent diabetes. These results accord with recent findings from longitudinal studies of impaired glucose tolerance in other populations.