Evening screen use may be more relaxing than stimulating for teenagers

A recent study published in the Journal of Sleep Research suggests that evening screen use might not be as physically stimulating for teenagers as many parents and experts have assumed. The findings provide evidence that most digital activities actually coincide with lower heart rates compared to non-screen activities like moving around the house or playing. This indicates that the common connection between screens and poor sleep is likely driven by the timing of device use rather than a state of high physical arousal.

Adolescence is a time when establishing healthy sleep patterns is essential for mental health and growth, yet many young people fall short of the recommended eight to ten hours of sleep. While screen use has been linked to shorter sleep times, the specific reasons why this happens are not yet fully understood.

Existing research has looked at several possibilities, such as the light from screens affecting hormones or the simple fact that screens take up time that could be spent sleeping. Some experts have also worried that the excitement from social media or gaming could keep the body in an active state that prevents relaxation. The new study was designed to investigate the physical arousal theory by looking at heart rate in real-world settings rather than in a laboratory.

“In our previous research, we found that screen use in bed was linked with shorter sleep, largely because teens were falling asleep later. But that left an open question: were screens simply delaying bedtime, or were they physiologically stimulating adolescents in a way that made it harder to fall asleep?” said study author Kim Meredith-Jones, a research associate professor at the University of Otago.

“In this study, we wanted to test whether evening screen use actually increased heart rate — a marker of physiological arousal — and whether that arousal explained delays in falling asleep. In other words, is it what teens are doing on screens that matters, or just the fact that screens are replacing sleep time?”

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By using objective tools to track both what teens do on their screens and how their hearts respond, the team hoped to fill gaps in existing knowledge. They aimed to see if different types of digital content, such as texting versus scrolling, had different effects on the heart. Understanding these connections is important for creating better guidelines for digital health in young people.

The research team recruited a group of 70 adolescents from Dunedin, New Zealand, who were between 11 and nearly 15 years old. This sample was designed to be diverse, featuring 31 girls and 39 boys from various backgrounds. Approximately 33 percent of the participants identified as indigenous Māori, while others came from Pacific, Asian, or European backgrounds.

To capture a detailed look at their evening habits, the researchers used a combination of wearable technology and video recordings over four different nights. Each participant wore a high-resolution camera attached to a chest harness starting three hours before their usual bedtime. This camera recorded exactly what they were doing and what screens they were viewing until they entered their beds.

Once the participants were in bed, a stationary camera continued to record their activities until they fell asleep. This allowed the researchers to see if they used devices while under the covers and exactly when they closed their eyes. The video data was then analyzed by trained coders who categorized screen use into ten specific behaviors, such as watching videos, gaming, or using social media.

The researchers also categorized activities as either passive or interactive. Passive activities included watching, listening, reading, or browsing, while interactive activities included gaming, communication, and multitasking. Social media use was analyzed separately to see its specific impact on heart rate compared to other activities.

At the same time, the participants wore a Fitbit Inspire 2 on their dominant wrist to track their heart rate every few seconds. The researchers used this information to see how the heart reacted to each specific screen activity in real time. This objective measurement provided a more accurate picture than asking the teenagers to remember how they felt or what they did.

To measure sleep quality and duration, each youth also wore a motion-sensing device on their other wrist for seven consecutive days. This tool, known as an accelerometer, provided data on when they actually fell asleep and how many times they woke up. The researchers then used statistical models to see if heart rate patterns during screen time could predict these sleep outcomes.

The data revealed that heart rates were consistently higher during periods when the teenagers were not using screens. The average heart rate during non-screen activities was approximately 93 beats per minute, which likely reflects the physical effort of moving around or doing chores. In contrast, when the participants were using their devices, their average heart rate dropped to about 83 beats per minute.

This suggests that screen use is often a sedentary behavior that allows the body to stay relatively calm. When the participants were in bed, the difference was less extreme, but screen use still tended to accompany lower heart rates than other in-bed activities. These findings indicate that digital engagement may function as a way for teenagers to wind down after a long day.

The researchers also looked at how specific types of digital content affected the heart. Social media use was associated with the lowest heart rates, especially when the teenagers were already in bed. Gaming and multitasking between different apps also showed lower heart rate readings compared to other screen-based tasks.

“We were surprised to find that heart rates were lower during social media use,” Meredith-Jones told PsyPost. “Previous research has suggested that social media can be stressful or emotionally intense for adolescents, so we expected to see higher arousal. Instead, our findings suggest that in this context, teens may have been using social media as a way to unwind or switch off. That said, how we define and measure ‘social media use’ matters, and we’re now working on more refined ways to capture the context and type of engagement.”

On the other hand, activities involving communication, such as texting or messaging, were linked to higher heart rates. This type of interaction seemed to be less conducive to relaxation than scrolling through feeds or watching videos. Even so, the heart rate differences between these various digital activities were relatively small.

When examining sleep patterns, the researchers found that heart rate earlier in the evening had a different relationship with sleep than heart rate closer to bedtime. Higher heart rates occurring more than two hours before bed were linked to falling asleep earlier in the night. This may be because higher activity levels in the early evening help the body build up a need for rest.

However, the heart rate in the two hours before bed and while in bed had the opposite effect on falling asleep. For every increase of 10 beats per minute during this window, the participants took about nine minutes longer to drift off. This provides evidence that physical excitement right before bed can delay the start of sleep.

Notably, while a higher heart rate made it harder to fall asleep, it did not seem to reduce the total amount of sleep the teenagers got. It also did not affect how often they woke up during the night or the general quality of their rest. The researchers noted that a person would likely need a very large increase in heart rate to see a major impact on their sleep schedule.

“The effects were relatively small,” Meredith-Jones explained. “For example, our data suggest heart rate would need to increase by around 30 beats per minute to delay sleep onset by about 30 minutes. The largest differences we observed between screen activities were closer to 10 beats per minute, making it unlikely that typical screen use would meaningfully delay sleep through physiological arousal alone.”

“The key takeaway is that most screen use in the evening did not increase heart rate. In fact, many types of screen activity were associated with lower heart rates compared to non-screen time. Although higher heart rate before bed was linked with taking longer to fall asleep, the changes in heart rate we observed during screen use were generally small. Overall, most evening screen activities appeared more relaxing than arousing.”

One limitation of this study is that the researchers did not have a baseline heart rate for each participant while they were completely at rest. Without this information, it is difficult to say for certain if screens were actively lowering the heart rate or if the teens were just naturally calm. Individual differences in biology could account for some of the variations seen in the data.

“One strength of this study was our use of wearable cameras to objectively classify screen behaviours such as gaming, social media, and communication,” Meredith-Jones noted. “This approach provides much richer and more accurate data than self-report questionnaires or simple screen-time analytics. However, a limitation is that we did not measure each participant’s true resting heart rate, so we can’t definitively say whether higher heart rates reflected arousal above baseline or just individual differences. That’s an important area for refinement in future research.”

It is also important to note that the findings don’t imply that screens are always helpful for sleep. Even if they are not physically arousing, using a device late at night can still lead to sleep displacement. This happens when the time spent on a screen replaces time that would otherwise be spent sleeping, leading to tiredness the next day. On the other hand, one shouldn’t assume that screens always impede sleep, either.

“A common assumption is that all screen use is inherently harmful for sleep,” Meredith-Jones explained. “Our findings don’t support that blanket statement. In earlier work, we found that screen use in bed was associated with shorter sleep duration, but in this study, most screen use was not physiologically stimulating. That suggests timing and context matter, and that some forms of screen use may even serve as a wind-down activity before bed.”

Looking ahead, “we want to better distinguish between different types of screen use, for example, interactive versus passive engagement, or emotionally charged versus neutral communication,” Meredith-Jones said. “We’re also developing improved real-world measurement tools that can capture not just how long teens use screens, but what they’re doing, how they’re engaging, and in what context. That level of detail is likely to give us much clearer answers than simple ‘screen time’ totals.”

The study, “Screens, Teens, and Sleep: Is the Impact of Nighttime Screen Use on Sleep Driven by Physiological Arousal?” was authored by Kim A. Meredith-Jones, Jillian J. Haszard, Barbara C. Galland, Shay-Ruby Wickham, Bradley J. Brosnan, Takiwai Russell-Camp, and Rachael W. Taylor.