Sleep stability, weight, and glycemic control

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Lifestyle changes are at the heart of diabetes prevention and management. In addition to diet and physical activity, sleep has emerged as an important behavior associated with glucose control. Recent studies further show that timing of these behaviors may be as important as their quality and quantity. For example, timing of sleep, independent of sleep duration, has been associated with obesity and metabolic syndrome, particularly glucose concentrations. In support of our study goals, we have shown that reducing variability in bedtimes improves body composition, measured by magnetic resonance imaging, compared to maintaining or increasing bedtime variability in women. While prior sleep research has focused on elucidating adverse health effects of too little sleep or poor sleep quality, we propose an innovative project in which we will test whether improvements in sleep behaviors, namely bedtime stability, ameliorates glycemia. Our main goal is to conduct a pilot clinical intervention study that will test whether reducing bedtime variability improves weight and glycemic control in patients with pre-diabetes. We will recruit men and post-menopausal women, age ³50 y, who have variable bedtimes (VS; standard deviation of bedtimes, measured over 14 d, >60 min). Participants will be randomized to maintain their habitual sleep patterns (VS) or reduce bedtime variability by following a fixed sleep schedule (FS) for 12 wk. Sleep will be monitored nightly using wrist actigraphy. In Aim 1, body adipose tissue distribution will be measured by magnetic resonance imaging (primary outcomes=total, subcutaneous, and visceral adipose tissue) and magnetic resonance spectroscopy (secondary outcome=liver fat). In Aim 2, we will assess glucose tolerance and insulin sensitivity via an oral glucose tolerance test (OGTT) at baseline and endpoint (primary outcome=glucose area under the curve; secondary outcomes=disposition index). Fasting plasma samples at baseline and endpoint will determine long-term glycemia (secondary outcomes=fructosamine and hemoglobin A1c). Finally, in Aim 3, we will assess variability in glucose concentrations, an independent risk factor for diabetes complications, using continuous glucose monitoring system for 14 d prior to study onset and in the last 2 wk of the intervention (primary outcomes=mean amplitude of glycemic excursion and standard deviation of mean glucose; secondary outcome=24-h average glucose concentrations). Diet and physical activity measures will be obtained throughout the intervention. This project has the potential to lead to larger-scale research study to provide more definitive information on the impact of maintaining stable bedtimes as a means to improve the health of adults at risk of type 2 diabetes and improve glycemic control in those living with this disease. This proposal addresses a highly novel and important research question and the