Delayed timing of post-challenge peak blood glucose predicts declining beta cell function and worsening glucose tolerance over time: insight from the first year postpartum.

AIMS/HYPOTHESIS: On cross-sectional assessment, a delayed timing of the peak blood glucose level at ≥60 min post-challenge on an OGTT is associated with beta cell dysfunction. In this context, we hypothesised that longitudinal changes in the timing of this peak might predict changes in glucose metabolism. We thus sought to evaluate the longitudinal associations of changes in the timing of the peak glucose level with changes over time in insulin sensitivity, beta cell function and glucose tolerance. METHODS: A total of 532 women underwent an OGTT at both 3 months and 12 months postpartum. The participants were stratified into four groups according to the change in timing of their glucose peak between the two visits: women with no change in timing of the glucose peak at 30 min (n = 217), those whose glucose peak shifted to an earlier time point (n = 120), those whose peak shifted to a later time point (n = 87) and women with an unchanged glucose peak at ≥60 min (n = 108). Beta cell function was measured using the Insulin Secretion-Sensitivity Index-2 (ISSI-2). RESULTS: Compared with an unchanged glucose peak at 30 min, both the shift of the glucose peak to a later time point and a peak that was unchanged at ≥60 min were independently associated with declining ISSI-2 scores (ß = -127.5, p < 0.001 and ß = -98.8, p = 0.006, respectively) and increased 2 h post-challenge glucose levels (ß = 1.28, p < 0.001 and ß = 0.91, p < 0.001, respectively) between the two visits. Furthermore, both these patterns of change in peak were independently associated with worsening glucose tolerance (from normal to prediabetes [defined as impaired fasting glucose or impaired glucose tolerance]/diabetes or from prediabetes to diabetes) (OR 8.1, 95% CI 3.0, 22.1 and OR 3.7, 95% CI 1.2, 11.7, respectively). CONCLUSIONS/INTERPRETATION: A delayed timing of the post-challenge peak glucose level is associated with declining beta cell function and worsening glucose tolerance over time.