Adolescents who sleep a little longer and tend to fall asleep earlier show stronger brain function and do better on cognitive tests than peers with later, shorter sleep, according to researchers in the UK and China.
The findings draw on objective sleep tracking and brain imaging, offering fresh evidence that modest changes in sleep habits may be linked to measurable differences in how the teenage brain works.
Researchers analyzed data from the Adolescent Brain Cognitive Development study in the United States, using Fitbit sleep measures from more than 3 200 participants aged 11 to 12 and comparing them with brain scans and cognitive testing.
They then checked whether similar patterns appeared in two additional groups aged 13 to 14, totaling about 1 190 participants, to see if the results held up beyond a single age snapshot.
The team identified three broad sleep profiles, with average sleep times ranging from about 7 hours 10 minutes to roughly 7 hours 25 minutes, a gap of just over 15 minutes between the shortest and longest sleepers.
Despite the small difference, adolescents in the longest-sleep group performed best on tests that assess skills such as vocabulary, reading, problem solving, and focus.
Brain measures differed across groups
Brain imaging also showed differences that tracked with sleep patterns, with the longest-sleep group showing the largest overall brain volume and stronger brain function measures, while the shortest-sleep group showed the smallest volume and weakest measures.
The study did not find significant differences in school achievement between groups, suggesting standardized academic outcomes may not capture the subtler cognitive effects observed in testing.
Heart-rate data during sleep pointed in the same direction: the longest-sleep group had the lowest heart rates across sleep states, while the shortest-sleep group had the highest.
Lower sleeping heart rates are generally associated with better cardiovascular health and can align with more stable, higher-quality sleep, while higher rates can accompany restless sleep and frequent awakenings.
Most teens still fell short
Even the best sleepers in the study were not reaching the amount of sleep typically recommended for adolescents, highlighting how widespread sleep shortfalls can be in early teen years.
The American Academy of Sleep Medicine advises that teenagers aged 13 to 18 should regularly sleep 8 to 10 hours per night for optimal health, while many fall below that range.
Because the dataset follows participants over time, researchers reported that differences in sleep patterns and related brain and cognitive measures appeared to persist across multiple years around the main assessment window.
The authors cautioned that the study cannot prove that better sleep directly causes better brain function, but they noted prior research supporting sleep’s role in memory consolidation and learning.
What could be driving later bedtimes?
The researchers said the next step is to better understand why some adolescents consistently go to bed later and sleep less, including potential influences such as evening screen use and individual body-clock differences.
They argue that identifying the drivers of sleep loss could help shape practical interventions, since the results suggest even small improvements in sleep timing and duration may matter.
