Overview

The proposed study uses a novel and rigorous randomized cross-over study design in youth (17-23y) with late and non-late chronotype (n=35 per group) to assess the glycemic effect of "aligning" an oral glucose tolerance test (OGTT) or first-meal of day to a subject's chronotype. Both groups will undergo 2 OGTTs (aligned and mis-aligned with chronotype) to compare glucose tolerance and insulin sensitivity within-subject (primary outcome) and between groups (Aim 1). Then, youth will also undergo two standardized meals (aligned and mis-aligned with chronotype) while wearing continuous glucose monitoring to compare post-prandial glucose excursions within-subject and between groups (Aim 2). A pilot Exploratory Aim 3 (n=12 per group) will investigate delayed melatonin patterns under dim-light as a potential pathophysiologic mechanism behind abnormal glucose tolerance in youth with late chronotype on morning OGTTs.

Eligibility

Inclusion Criteria:

• Overweight similar to (BMI ≥ 85th percentile but <95th percentile for age and sex per Centers for Disease Control and Prevention growth curves (as Centers for Disease Control and Prevention growth curves contain ages ≤ 20y; if ages 21-23 years, the BMI ≥ 85th and <95th percentile equivalents for a 20-year-old will be used))
• Post-pubertal
• Normal sleep duration (avg. >7 hours of sleep per night)
• Social jetlag (difference between weekend and weekday sleep) of < 2 hours.

Exclusion Criteria:

• Known diabetes, sleep disorders, major organ system illness, pregnancy, or genetic syndrome
• Medication use known to affect insulin sensitivity, glucose tolerance, or circadian rhythm
• Screening high risk for obstructive sleep apnea
• Night shift work.