Late-Evening Smartphone Use Linked to Poorer Sleep in Adolescents: JAMA

A new study published in the Journal of American Medical Association showed that higher cumulative smartphone usage late in the evening was related with delayed sleep initiation, later awakening and shorter total sleep time (TST).

Smartphone usage has been linked to issues with sleep, but the current evidence mostly comes from self-reported and cross-sectional data. This study looked at both individual-level and group-level connections between passive tracking of smartphone use in the evening and actual, measured sleep results in teenagers.

This study looked at data collected from US teenagers participating in the Adolescent Brain Cognitive Development Study. The participants used Android smartphones and had at least 14 days of data from the Effortless Assessment Research System app along with sleep data from Fitbit devices. Data was gathered from November 30, 2020, to February 5, 2024, and analyzed from February 2 to June 1, 2026.

The analysis used a statistical method called within-between decomposition in multilevel models to distinguish between patterns that vary within a person over time and those that differ between individuals. The study measured smartphone use during specific times: the total use from 8 p.m.to midnight each hour and the use that happened within 5 to 30 minutes before the person went to sleep.

A total of 425 participants provided 7,591 person-nights of data. On nights when adolescents used their phones more than their usual evening average after 10 pm, they slept an average of 20.05 minutes less and took about 64.73 minutes longer to fall asleep.

After taking into account other factors, the analysis showed that for each extra minute of smartphone use after 10 pm compared to their usual average, sleep onset was delayed by 0.87 minutes (95% confidence interval, 0.84 to 0.90), sleep offset was delayed by 0.37 minutes (95% confidence interval, 0.33 to 0.41), and TST decreased by 0.43 minutes (95% confidence interval, −0.47 to −0.39) (all P < .001).

These effects increased steadily as the cutoff time for phone use moved from 8 pm to midnight. Recent use was linked to more prolonged wakefulness after sleep onset, with the strongest effect seen in the last 5 minutes before falling asleep. However, this effect was minimal when looking at the last 20 minutes before sleep onset. The link between phone use and wakefulness was mainly observed in the first 30 minutes after falling asleep.

Overall, increased use of phones during late evenings was linked to going to sleep later, staying awake longer, and having less total sleep time. These results indicate that limiting smartphone use in the evening, especially after 10 pm and right before going to bed, could help enhance sleep quality among teenagers.

Source:

Zhao, Y., Hale, L., & Christakis, D. A. (2026). Evening phone use and sleep outcomes among youth. JAMA Pediatrics. https://doi.org/10.1001/jamapediatrics.2026.4902