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. He is a professor in the Department of Cell and Molecular Physiology of Loyola University Chicago Stritch School of Medicine.

“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).