Interplay of Dinner Timing and MTNR1B Type 2 Diabetes Risk Variant on Glucose Tolerance and Insulin Secretion: A Randomized Crossover Trial
Research Design and Methods: In a Spanish natural late eating population, a randomized, cross-over study design was performed, following an 8-h fast. Each participant (n=845) underwent two evening 2-h 75g oral glucose tolerance tests (OGTT): an early condition scheduled 4 hours prior to habitual bedtime (“early dinner-timing”), and a late condition scheduled 1 hour prior to habitual bedtime (“late dinner-timing”), simulating an early and a late dinner timing, respectively. Differences in postprandial glucose and insulin responses were determined using incremental area under the curve (AUC) calculated by the trapezoidal method between early and late dinner-timing.
Results: Melatonin serum levels were 3.5-fold higher in the late vs. early condition, with late dinner-timing resulting in 6.7% lower insulin area-under-the-curve (AUC) and 8.3% higher glucose AUC. In the late condition MTNR1B G-allele carriers had lower glucose tolerance than non-carriers. Genotype differences in glucose tolerance were attributed to reductions in β-cell function (Pint AUCgluc=0.009, Pint CIR=0.022, Pint DI=0.018).
Conclusions: Concurrently high endogenous melatonin and carbohydrate intake, as typical for late eating, impair glucose tolerance, especially in MTNR1B G-risk-allele carriers, attributable to insulin secretion defects.