Study participants will complete two 10-day inpatient stays in the sleep laboratory of the University of Chicago Clinical Resource Center scheduled at least 4 weeks apart. Bedtime duration will be set at 5 hours per night during one of these stays and 8.5 hours per night during the other. No daytime naps will be allowed. Study participants will be served regular daily meals including breakfast, lunch, dinner, and a bedtime snack. On weekdays all participants will engage in simulated "office work" while in the sleep laboratory. During the rest of the time participants will maintain their usual indoor and outdoor activities as much as possible within the limits of the University of Chicago campus. During the last two days of each inpatient stay in the laboratory, participants will undergo two different tests. The first test will determine how much insulin does their body produce in response to an intravenous glucose infusion lasting several hours. The second test will determine how effective is the action of the sugar-processing hormone, insulin, in their body when it is infused intravenously together with glucose over a period of several hours.