Teens’ weekend sleep habits may be harming their brains

Teens don’t just stay up late on weekends – they shift their entire sleep schedule. And a new study shows that this weekly back-and-forth, known as social jet lag, is incredibly common.

More than 35 percent of adolescents regularly bounce between weekday and weekend sleep patterns, and their brains feel the impact.

A team from Boston Children’s Hospital and Johns Hopkins All Children’s Hospital dug into brain scans from thousands of U.S. adolescents to understand what that mismatch really means.

The results suggest that changing sleep timing – not just getting too little sleep – may quietly shape how key brain networks develop.

Why teen sleep timing gets tricky

The circadian rhythm, the internal 24-hour timing system for sleep, tends to run later during puberty than in childhood.

Light at night can delay melatonin, a hormone that helps the brain start to sleep, especially when phones stay nearby.

Even when total sleep looks fine, irregular timing can affect mood, attention, and how the brain stores memories from day to day.

Early buses and first-period classes force wake-up times earlier than many teens can manage, so timing problems grow.

Tracking weekend timing shifts

Researchers tapped the Adolescent Brain Cognitive Development study, often called the ABCD Study, to follow brain growth nationwide.

The sample included 3,507 youth, mostly age 12, and the team compared weekend and school-night sleep timing across ABCD Study participants.

The team focused on the sleep midpoint, halfway between falling asleep and waking, because it captures when a person truly sleeps.

To separate timing from length, the researchers calculated social jet lag with and without an adjustment for weekday sleep debt.

Teen brain network changes emerge

Each teen completed resting-state functional magnetic resonance imaging (fMRI), a brain scan mapping synchronized activity while resting, which reveals networks that communicate together.

Longer social jet lag came with weaker links from the thalamus, a deep hub that routes signals and shapes arousal.

The salience network, the brain system that flags important internal and external cues, also showed lower connectivity with more mismatch.

The researchers also saw weaker connections in the dorsal attention network, the brain system that supports sustained, goal-driven focus.

Altered circuits and flow

In the same brain data, longer mismatch was related to lower topological resilience, the ability of a network to stay connected under stress.

The experts found smaller regions for reward processing – how the brain learns from pleasure and motivation – plus areas linked to emotion and social cues.

Measures of information transfer, how efficiently brain regions share signals, were lower across areas involved in social function and emotion regulation.

The team also reported changes in intrinsic dynamics, natural patterns of brain activity that rise and fall, during quiet rest in the scanner.

Teen groups with sleep mismatches

The team flagged a two-hour gap in sleep midpoint between school nights and weekends as severe social jet lag.

Boys, Hispanic youth, Black non-Hispanic youth, and teens farther along in puberty tended to report longer misalignment in this sample.

Longer misalignment was also related to higher body mass index in this adolescent group. 

The question is, could those group patterns reflect differences in school demands, household routines, or stress rather than biology alone?

Consequences for teen behavior

When thalamus links weaken, the brain may filter sensory input less smoothly, and emotional reactions can feel harder to manage.

With less steady salience signaling, attention can jump around, and the brain may miss cues that help guide decisions at school.

If goal-driven attention circuits run weaker, sustained reading, test-taking, or careful driving can demand more effort and time.

Lower information sharing across social and emotion systems may matter for friendships, conflict, and the quick judgments teens face every day.

Interpreting the sleep data

Because the work links sleep timing and brain measures at one point in time, it cannot show what causes what for each teen.

Stress, depression symptoms, caffeine, screen habits, and family schedules can affect sleep timing and brain health at the same time for adolescents.

Social jet lag depends on typical weekday and weekend timing, and a single week can look very different from another.

Future analyses in the ABCD Study may track whether sleep routines predict brain changes over years, not just months.

Expert guidance on teen sleep

The American Academy of Sleep Medicine recommends that teens age 13 to 18 sleep eight to ten hours each day.

A national youth survey found that about one in four students got at least eight hours on school nights in 2023.

The American Academy of Pediatrics urged middle and high schools to start at 8:30 a.m. or later. Those recommendations focus on sleep length, but this new brain work makes stable bed and wake times more important.

What consistency looks like at home

Families often find it easier to set a steady wake time, because that consistent wake time makes bedtimes come earlier on school nights.

Reducing bright light and scrolling in the hour before bed can help melatonin rise and keep sleep timing consistent.

“Social jet lag may have extensive detrimental effects on the adolescent brain,” said Dr. Catherine Stamoulis from Boston Children’s Hospital, who led the research.

Small schedule changes can help, but real progress often needs school policies, evening demands, and family routines to align.

The study is published in the journal SLEEP.

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