Problems related to definitions and epidemiology of type 2 (non-insulin-dependent) diabetes mellitus: studies throughout the world.

Many studies of Type 2 (non-insulin-dependent) diabetes mellitus assume that the condition is homogeneous and clearly defined. There are, however, several problems with these assumptions. Thus, definition of Type 2 diabetes is one of exclusion of other types (insulin-dependent, malnutrition-related, gestational and other rarer types) and inevitably contains a heterogeneous group of disorders the aetiology of which is largely unclear, and separation from the insulin-dependent type can be problematic. Diagnosis is also imprecise in asymptomatic subjects due to the lack of accurate diagnostic tools and lack of clear distinction of impaired glucose tolerance. An alternative to the oral glucose tolerance test is urgently needed. Epidemiological studies of Type 2 diabetes and its complications are also fraught with difficulties due to variability of the oral glucose tolerance test, potential problems in glucose measurement, heterogeneity, population selection and problems in international comparisons due to differing age structures and life expectancy. Great care is needed in all studies of Type 2 diabetes to ensure that the groups under study are properly selected, well-defined and fully described.