More than half pick up their phones between midnight and 4 a.m.
Por quase dois anos, pesquisadores da Universidade da Califórnia em San Francisco observaram silenciosamente o que os adolescentes americanos fazem nas horas mais escuras da madrugada — e descobriram que mais da metade deles troca o sono pelas telas. Publicado na JAMA Pediatrics, o estudo não se baseou em declarações dos próprios jovens, mas em registros reais de uso, revelando um padrão que coloca em xeque a saúde mental, o desempenho escolar e a equidade entre gerações. É uma imagem de uma época em que as plataformas digitais competem, com vantagem, contra o descanso humano.
- Mais de 52% dos adolescentes americanos acessam o celular entre meia-noite e 4h em noites de semana, roubando em média 50 minutos do sono recomendado.
- TikTok, Instagram e YouTube dominam 65% desse tempo noturno — não são mensagens urgentes nem tarefas escolares, mas feeds intermináveis projetados para prender a atenção.
- A perturbação não é igualitária: jovens negros e de famílias de baixa renda apresentam índices significativamente maiores de uso noturno, aprofundando desigualdades já existentes.
- Pesquisadores apontam que apenas 10 a 15 minutos a mais de sono por noite já produzem melhorias mensuráveis na saúde mental e na cognição — tornando o problema também uma oportunidade de intervenção.
- O estudo tem limites reconhecidos: só rastreou dispositivos Android, não mediu o sono diretamente e não pode provar causalidade — mas a escala do fenômeno já justifica atenção pública urgente.
Pesquisadores da Universidade da Califórnia em San Francisco acompanharam 657 adolescentes americanos com média de 15 anos entre setembro de 2022 e maio de 2024, usando um software instalado diretamente nos celulares para registrar o uso real — não o que os jovens acreditavam fazer. O resultado é inquietante: mais da metade deles pega o telefone entre meia-noite e 4h em noites de semana.
Durante o período que deveria ser de descanso — entre 22h e 6h —, esses adolescentes passaram em média 50 minutos diante das telas. Um quarto deles ultrapassou 71 minutos por noite. Mais de 65% desse tempo foi consumido em redes sociais como TikTok, Instagram e YouTube, com média de 32,7 minutos. Não se trata de mensagens urgentes ou deveres escolares: é rolagem de feed na madrugada.
As consequências vão além do cansaço. A privação de sono fragmenta a recuperação mental que os adolescentes precisam para aprender e regular as emoções. Os pesquisadores destacam que mesmo pequenos ganhos — de 10 a 15 minutos a mais de sono — se traduzem em melhorias cognitivas e de saúde mental mensuráveis.
Os dados também expõem desigualdades. Meninos usaram mais redes sociais à noite do que meninas. Adolescentes negros e de famílias de menor renda apresentaram tempo de tela noturno significativamente superior ao de seus pares — sugerindo que o impacto recai de forma desproporcional sobre jovens que já enfrentam outras pressões.
O estudo tem limitações: o rastreamento funcionou apenas em dispositivos Android, o sono não foi medido diretamente e o desenho transversal impede afirmar causalidade. Mas o retrato que emerge — de uma geração alcançando o celular nas horas em que deveria dormir, atraída por plataformas construídas para não largar — é suficientemente nítido para exigir respostas.
Researchers at the University of California in San Francisco spent nearly two years watching how American teenagers use their phones in the middle of the night, and what they found is stark: more than half of them pick up their devices between midnight and 4 a.m. on school nights. The study, published Monday in JAMA Pediatrics, tracked 657 adolescents with an average age of 15 from September 2022 through May 2024, using software installed directly on their phones to record actual usage patterns rather than relying on what teenagers themselves reported.
The numbers reveal a consistent pattern of sleep disruption. During the hours typically reserved for rest—between 10 p.m. and 6 a.m.—these teenagers averaged 50 minutes of screen time per night. A quarter of them spent more than 71 minutes staring at their phones during those hours. The researchers emphasize that this window corresponds to the sleep duration recommended for adolescents, meaning that time on a phone is time not spent sleeping.
What dominates that nighttime screen time is social media. More than 65 percent of the nightly phone use went to platforms like TikTok, Instagram, and YouTube, averaging 32.7 minutes per night. Entertainment apps like Netflix and gaming applications filled the remainder. The pattern suggests that teenagers are not checking urgent messages or doing homework in the dead of night—they are scrolling through feeds and watching videos.
The study's methodology sets it apart from earlier research. Rather than asking teenagers to estimate their own usage, researchers deployed the Effortless Assessment Research System, or EARS, which tracked phone activity in real time without depending on self-reporting. This distinction matters because teenagers, like most people, tend to underestimate how much time they spend on their devices. The researchers followed participants across nearly two years, capturing patterns across seasons and school schedules.
The consequences of this nighttime usage extend beyond simple fatigue. Sleep disruption at this scale can delay, displace, or fragment the restorative sleep that adolescents need for healthy mental function and academic performance. The researchers note that even modest extensions of sleep—just 10 to 15 minutes more per night—correlate with measurable improvements in cognitive function and mental health. This suggests that the 50 minutes teenagers are spending on phones could, if redirected to sleep, produce meaningful gains in how they think and feel.
The data also reveals disparities in who is most affected. Boys spent more time on social media at night than girls. Black adolescents and teenagers from lower-income families showed significantly higher nighttime screen time than their peers. These patterns suggest that the sleep disruption caused by phones is not evenly distributed across the teenage population—it falls more heavily on young people already navigating other stressors.
The study has acknowledged limits. The research design is cross-sectional, meaning it cannot prove that phone use directly causes sleep problems, only that the two occur together. The tracking software only worked on Android devices, excluding iPhone users. And the researchers did not measure sleep directly; they inferred sleep disruption from the timing of phone use. They are calling for future research that directly measures how much sleep teenagers actually get and how that correlates with their phone habits, mental health, and grades.
What emerges is a portrait of a generation reaching for their phones in the hours when they should be sleeping, pulled by platforms designed to hold their attention. Whether this is a cause of poor sleep or a symptom of it remains an open question. But the scale of the behavior—more than half of American teenagers doing this on school nights—suggests it is a public health issue worth understanding more deeply.
Notable Quotes
Even 10 to 15 minutes of additional sleep correlates with measurable improvements in cognitive function and mental health— JAMA Pediatrics study researchers
The Hearth Conversation Another angle on the story
Why does it matter that they're using phones specifically between midnight and 4 a.m.? Couldn't they be checking the time or responding to something urgent?
The researchers found that 65 percent of the time was spent on social media—TikTok, Instagram, YouTube. That's not urgent communication. That's scrolling. And midnight to 4 a.m. is when the body is supposed to be in deep sleep. It's not about the activity itself; it's about when it's happening.
The study says it can't prove the phones are causing the sleep loss. So maybe these are just teenagers who already have insomnia, and they're reaching for their phones because they can't sleep?
That's a fair question, and the researchers acknowledge it. But think about it this way: if you're lying in bed and you pick up your phone, the light from the screen suppresses melatonin production. Even if you couldn't sleep before, the phone makes it worse. The causality probably runs both directions.
The disparities are interesting—Black teenagers and lower-income kids using phones more at night. What's driving that?
The study doesn't explain why, just documents that it happens. But you could imagine several factors: maybe less stable home environments, more stress, fewer resources for other activities. Or maybe it's about access—some families can't afford consistent internet during the day, so kids use it when they can at night. The study raises the question without answering it.
If even 10 to 15 minutes more sleep helps, why isn't this a bigger public health priority?
It might become one. Right now, most of the conversation around teen phones focuses on social comparison and mental health directly. This study is saying: forget those debates for a moment, just look at sleep. Teenagers are losing an hour of sleep per night because of their phones. That alone should matter to schools, parents, and health officials.