High school students slept around 45 minutes more per night after their school start times were delayed.
CNN  — 

Changing middle and high school schedules can lead to significantly improved shut-eye for students, a new study found.

Researchers surveyed around 28,000 students in the Cherry Creek School District in Colorado over two years and found moving school start times later in the morning resulted in increased sleep times of around 45 minutes for students, according to research published Thursday in the journal Sleep.

Since many districts stagger their school buses in order to pick up everyone, the elementary school students began school an hour earlier over the course of the study so that older students could be picked up later, said study author Lisa Meltzer, a pediatric psychologist at National Jewish Health in Colorado.

She said the research team found no significant difference in elementary school students’ sleep times after the hour change.

The middle schools delayed their start times by 40 to 60 minutes, and high schools delayed theirs by 70 minutes to ensure they started at or after 8:30 a.m.

Middle school students went to bed an average of nine minutes later, but slept in an additional 37 minutes, giving them an average of 29 minutes of extra sleep. High school students went to bed an average of 14 minutes later, but slept for an additional 60 minutes, allowing them to sleep 46 minutes more on average.

“Delaying middle and high school start times is a critical health policy that can quickly and effectively reduce adolescent sleep deprivation with minimal impact on younger students,” Meltzer said.

The study results also allude to “social jet lag” among teenagers, said Brant Hasler, associate professor of psychiatry at the University of Pittsburgh, who was not involved in the study. He described social jet lag as, “the mismatch between the early schedules that schools impose and (teens’) biological tendency toward being night owls.”

Teenagers often have a three-hour difference between their school-week and weekend time zones, and the latter aligns better with their internal biological clock, Hasler said.

He compared it to flying from San Francisco to New York each week.

“Think about the jetlag that you felt in the days after you returned, and then imagine the impact on your well-being of doing it every week for 9 months of the year,” Hasler said in an email.

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When students don’t get enough sleep – which he said is up to nine hours per night for teenagers – it can negatively affect their memory, learning ability, and mental and physical health, Hasler added.

The study mainly focused on the consequences of delaying middle and high school start times, so Meltzer wants to focus future research on finding out the optimal start times for elementary students as well.

Sufficient sleep is crucial for all students, especially teenagers, Hasler said, and early school start times are the primary obstacle teens face to getting enough sleep.

“If you give teens the chance to get the sleep they need by shifting start times later, they will embrace this opportunity,” Hasler said.