Insulin resistance and β-cell dysfunction in individuals with normal glucose tolerance but elevated 1-h post-load plasma glucose.

Objective: Diabetes and its complications impose a significant burden on public health, necessitating early identification and intervention, yet current prediabetes diagnostic criteria may not fully capture all high-risk individuals. Evaluate and compare insulin resistance (IR) and β-cell dysfunction in individuals with normal glucose tolerance (NGT) and 1-hour post-load plasma glucose (1-h PG) ≥ 8.6 mmol/L versus < 8.6 mmol/L, as well as prediabetes based on IFG and/or IGT. Research design and methods: This retrospective study included individuals at risk for diabetes who underwent an Oral Glucose Tolerance Test (OGTT), classified as having NGT or prediabetes according to ADA criteria. IR and β-cell dysfunction were assessed using the Matsuda index, insulinogenic index (IGI30), and oral disposition index (DI). Results: Among the 9,452 participants, 37.8% had NGT, and 62.2% were IFG or IGT in OGTT. Of the NGT group, 39.2% had a 1-h PG ≥ 8.6 mmol/L, with a higher mean age (53 vs. 47 years for those with 1-h PG < 8.6 mmol/L). Glucose and insulin curves showed that the NGT group with 1-h PG ≥ 8.6 mmol/L exhibited glucose profiles similar to those with isolated impaired fasting glucose (I-IFG), marked by elevated glucose, early insulin secretion impairment, and delayed insulin peaks. Older individuals (≥ 65 years) had higher glucose and a higher prevalence of abnormal 1-h PG but showed no significant differences in IR or β-cell dysfunction compared to younger individuals. Conclusions: A 1-h PG ≥ 8.6 mmol/L in individuals with NGT is associated with substantial β-cell dysfunction, highlight the value of incorporating 1-h PG measurement into diagnostic assessments for early detection of insulin secretion impairments across age groups.