How much sleep do we really need?

The panel, convened by the National Sleep Foundation, is making its recommendations based on age, ranging from newborns (who need 14 to 17 hours of sleep per day) to adults aged 65 and up (7 to 8 hours per day).

In the new guidelines, there's a wider range of what constitutes a good night's sleep. For example, the expert panel recommends that teens (ages 14 to 17) get 8 to 10 hours of sleep per night. The previous guideline had a narrower recommended range of 8.5 to 9.5 hours per night.

Dr. DonCarlos and other experts on the multidisciplinary panel examined findings from 320 studies reporting sleep duration findings for healthy individuals, effects of reduced or prolonged sleep duration and health consequences of too much or too little sleep. Results are published in Sleep Health: Journal of the National Sleep Foundation.

"The process was very rigorous," Dr. DonCarlos said. Dr. DonCarlos is a professor in the Department of Cell and Molecular Physiology of Loyola University Chicago Stritch School of Medicine.

The expert panel consists of 12 representatives, including Dr. DonCarlos, who were selected by medical organizations; and six sleep experts selected by the National Sleep Foundation. Dr. DonCarlos represents the American Association of Anatomists.

Dr. DonCarlos is a neuroendocrinologist who studies how hormones affect the structure of the brain. The section of the brain responsible for regulating hormone production is the hypothalamus. Hormones produced by the hypothalamus govern body temperature, hunger, stress responses, sex drive, circadian rhythms and sleep.

In addition to serving on the National Sleep Foundation expert panel, Dr. DonCarlos serves on the National Institutes of Health's Neuroendocrinology, Neuroimmunology, Rhythms and Sleep (NNRS) study section, which reviews applications for research grants.

"We still have a great deal to learn about the function of sleep," Dr. DonCarlos said. "We know it's restorative and important for memory consolidation. But we don't know the details of what the function of sleep is, even though it is how we spend one-third of our lives."

These are the sleep-time recommendations from the National Sleep Foundation expert panel:

• Newborns (0-3 months): Sleep range narrowed to 14-17 hours each day (previously it was 12-18).
• Infants (4-11 months): Sleep range widened two hours to 12-15 hours (previously it was 14-15).
• Toddlers (1-2 years): Sleep range widened by one hour to 11-14 hours (previously it was 12-14).
• Preschoolers (3-5): Sleep range widened by one hour to 10-13 hours (previously it was 11-13).
• School age children (6-13): Sleep range widened by one hour to 9-11 hours (previously it was 10-11).
• Teenagers (14-17): Sleep range widened by one hour to 8-10 hours (previously it was 8.5-9.5).
• Younger adults (18-25): Sleep range is 7-9 hours (new age category).
• Adults (26-64): Sleep range did not change and remains 7-9 hours.
• Older adults (65+): Sleep range is 7-8 hours (new age category).