Each extra half hour on the phone after 10 PM costs a teen about 13 minutes of sleep
STUDY: Zhao Y et al, JAMA Pediatrics 2026
STUDY TYPE: Cohort study
FUNDING: Columbia University Research Revitalization Award
Background
Phones are blamed for poor teen sleep, but most evidence relies on self-reported screen time. This study used objective data to test whether teens sleep worse on heavier phone nights.
The Study
- 425 teens (average age 15) from the Adolescent Brain Cognitive Development Study, all Android users.
- An app logged phone use and a Fitbit measured sleep for a median of 18 nights.
- Each teen’s heavier phone nights were compared with their own typical nights.
- Outcomes: sleep onset, wake time, total sleep, and time awake after falling asleep.
Results
Thirty extra minutes of use after 10 PM was linked to falling asleep 26 minutes later, waking 11 minutes later, and losing 13 minutes of sleep. The later the use, the stronger the link, peaking after midnight.
Phone use in the final 5 to 15 minutes before sleep was linked to more time awake in the first 30 minutes of the night. The effect was small and faded when use ended 20 or more minutes before sleep.
Phone use was common. Teens used their phones after 10 PM on two-thirds of nights, averaging 40 minutes, mostly on social media.
Limitations
Although comparing teens with themselves removes stable differences like temperament, it can’t rule out reverse causation: on nights a teen isn’t sleepy, the phone comes out. The sample was limited to Android users, and wrist trackers measure sleep imprecisely.
Practice Implications
- Blue light and activating apps disrupt sleep, and that means more ADHD symptoms, mood problems, and impulsivity.
- Recommend a 10 PM phone curfew, a 20-minute phone-free buffer before lights out, and charging the phone outside the bedroom.
—Chris Aiken, MD
Director, Psych Partners
Editor in Chief, Carlat Psychiatry Report
