Examining the Biological Factors That Affect Sleep Duration

The amount of sleep people require depends on many factors, including age, but experts agree
that most adults need 7 to 8 hours of sleep a night. People who sleep for shorter or longer
amounts of time may be at risk of developing memory problems, heart disease, obesity, and
diabetes. The duration and timing of sleep are regulated by an interaction between the
circadian pacemaker, or biological clock, and the sleep homeostat, which is an internal
account of the amount of sleep a person has received recently. It is unknown whether there
is a biological or genetic basis for the amount of sleep a person needs. This inpatient
study will examine two extreme sleep groups: short sleepers who sleep 6.5 or less hours a
night and long sleepers who sleep 9 or more hours a night. Participants will be exposed to
identical sleep opportunities and living conditions. Using hormone analysis to examine
participants' circadian rhythms, researchers will evaluate the biological differences that
people undergo during the sleep process. Results from this study may help researchers
understand whether sleep duration and sleep needs differ among people because of biological
and genetic variations.

Over a period of 4 to 6 weeks, potential study participants will attend 4 to 6 screening
visits, which will include a medical history review, physical exam, blood and urine
collection, electrocardiogram (EKG) to measure electrical activity of the heart, a
psychological assessment, and an overnight stay in a sleep laboratory. For 3 weeks,
potential participants will also wear an activity monitor, and they will record sleep habits
electronically and in a daily diary.

Participants who are eligible for the study will spend 28 days in the Intensive
Physiological Monitoring Unit of the Clinical and Translational Sciences Center at the
Brigham and Women's Hospital. Participants will not have access to a clock, radio,
television, or computer, and they will not be allowed any outside contact. Most days
participants will remain in bed for 10 to 14 hours; however, at selected times during the
study, participants will remain inactive for periods of 32 to 64 hours and will stay awake
for 32 to 40 hours. Throughout the study, participants' sleep patterns will be monitored
continuously by a wrist activity recorder. Heart rhythms, brain electrical activity, eye
movements, and temperature will also be measured continuously. At different times throughout
the study, participants will undergo urine, saliva, and blood collection; alertness, mood,
and performance evaluations; and blood pressure measurements. Upon release from the research
center, participants will maintain a sleep diary for 3 weeks.

Inclusion Criteria:

- Routinely sleeps 6.5 hours or less a night, or routinely sleeps 9 hours or more a
night

- In good health

Exclusion Criteria:

- Diagnosed with a sleep disorder

- Currently uses medications

- Performed night shift work in the 3 years before study entry

- History of psychiatric illness