1-hour postload glucose is a more sensitive marker of impaired β-cell function than 2-hour postload glucose

There is evidence that 1-h plasma glucose (PG) during the 75-g oral glucose tolerance test (OGTT) is superior to 2-h PG in predicting diabetes. We aimed to investigate the characteristics of insulin sensitivity and β-cell function behind this observation. After age, sex and BMI matching, 496 subjects selected from 3965 non-diabetic individuals at high risk of type 2 diabetes in a tertiary medical center were categorized into four groups in a 1:1:1:1 ratio based on OGTT results: 1) 1 h < 8.6 mmol/L and 2 h < 7.8 mmol/L (normal glucose tolerance [NGT] /1h-normal); 2) 1 h ≥ 8.6 mmol/L and 2 h < 7.8 mmol/L (NGT/1h-high); 3) 1 h < 8.6 mmol/L and 2 h ≥ 7.8 mmol/L (impaired glucose tolerance [IGT]/1h-normal); and 4) 1 h ≥ 8.6 mmol/L and 2 h ≥ 7.8 mmol/L (IGT/1h-high). Compared with subjects with IGT/1h-normal, those with NGT/1h-high exhibited similar extent of insulin resistance but lower early-phase insulin secretion. Additionally, participants with NGT/1h-high had lower disposition index at both 0-30 min and 0-120 min than those with IGT/1h-normal. The fitted regression line relating PG to log-transformed disposition index (0-30 min and 0-120 min) was significantly steeper for 1-h than 2-h PG. In conclusion, 1-h PG seemed to be more sensitive to the deterioration in β-cell function than 2-h PG. The use of 1-h PG may identify individuals at high risk of type 2 diabetes at an earlier stage.