Longitudinal insights into the natural history of Type 2 diabetes among Koreans: A 20-year community-based prospective cohort study.

Objective: To investigate the natural history of diabetes mellitus (DM) based on metabolic phenotypes of prediabetes in a community-based prospective study.

Methods: Individuals aged 40-69 years without DM were followed for 20 years. Glycemic parameters, including the 75 g oral glucose tolerance test, were assessed at baseline and biennially thereafter. Markov models were used to estimate each glycemic state's annual transition probabilities and average total length of residence.

Results: Among the 7,676 participants without DM, 205 had isolated impaired fasting glucose (iIFG), and 1,753 had impaired glucose tolerance (IGT) at baseline. During the 17.5 years of follow-up, 2,313 (30.1%) cases of DM occurred. The annual transition to DM for those with iIFG was 7.7% (95% confidence interval [CI] 6.9, 8.5) and 6.9% (95% CI 6.6, 7.3) for those with IGT. In the normoglycemia ↔ iIFG → DM model, the total length in normoglycemia was 49.4 years (95% CI 47.0, 52.1), and the length in iIFG was 6.3 years (95% CI 5.9, 6.8). In the normoglycemia ↔ IGT → DM model, the total length in normoglycemia was 34.0 years (95% CI 32.4, 35.4), and the length in IGT was 11.9 years (95% CI 11.1, 12.5).

Conclusions: Individuals remained normoglycemic for long periods. However, the progression to DM occurs rapidly once prediabetes develops, regardless of the metabolic phenotype.