Biomarkers of Increased Free Living Sleep Time

Inclusion Criteria:

1. 18-35 years old; men and women a. Equal numbers of women and men will be included.

2. Body Mass Index (BMI) of > 18.5 and <24.9.

3. Inactive to habitual moderate physical activity level (<5 days of exercise perweek).

4. Sleep/wake history: habitual sleep duration less than 6 hours per night.

5. Altitude history: Potential participants must have lived at Denver altitude orhigher for at least 3 months.

Exclusion Criteria:

1. Any clinically significant unstable medical or surgical condition within the lastyear (treated or untreated).

2. Any clinically significant psychiatric condition, as defined by DSM-IV-TR. I

3. Any clinically significant sleep disorder.

4. Use of prescription medications/supplements within one month or need of thesemedications at any time during the study.

5. Symptoms of active illness (e.g., fever).

6. Uncorrected visual impairment

7. History of shift work in prior year or travel more than one time zone in three weeksprior to study.

8. Participants must be entirely drug-free of illicit drugs, medications, nicotine andherbal products for one month prior to study.

9. Blood donation in the 30 days prior to inpatient study.

10. Ovulating women will be selected on the basis of a history of regular menstrualcycle ranging in length from 25-32 days with a maximum of three days variationmonth-to-month. They will have no history of prior gynecological pathology, be atleast 1 year post-partum, not breast-feeding and not pregnant (HCG pregnancy test atscreening and upon admission to the inpatient protocol).