Smartphone use before bed? It might not be as bad for teen sleep as thought, study finds

A new study published in Computers in Human Behavior challenges the conventional wisdom about the negative impact of smartphone use on adolescent sleep. Contrary to expectations, researchers failed to find a clear link between teens’ smartphone use before sleep and their sleep outcomes. This suggests that the impact of smartphones on sleep may be more complex than previously thought.

The use of electronic media devices, especially smartphones, has become increasingly prevalent among adolescents in many parts of the world. Smartphones are unique in that they are often used in close proximity to the user’s face and shortly before sleep. This has led to concerns that smartphone use before bedtime may interfere with sleep more than other electronic devices like laptops or tablets. Previous research has shown that inadequate sleep is associated with various negative outcomes, including academic performance, obesity, mental health issues, and more.

While numerous studies have explored the relationship between smartphone use and adolescent sleep, there have been limitations in the research. Most prior studies have been cross-sectional, making it challenging to establish causal links between smartphone use and sleep problems. Additionally, these studies often treat smartphone use as a stable behavior pattern, ignoring the day-to-day variations in sleep and media use patterns.

This study aimed to address these limitations by using an electronic daily diary design and objective measurements of smartphone use to examine both between-person and within-person associations between adolescents’ smartphone use before sleep and various sleep outcomes.

“Nowadays, many parents share concerns about how smartphones impact their children’s sleep and wonder if they should implement some parenting strategies related to their children’s smartphone use before bedtime,” said study author Michał Tkaczyk, a postdoctoral researcher at the Interdisciplinary Research Team on Internet and Society (@irtis_muni) at Masaryk University.

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“Prior research showed that adolescents often use smartphones in bed, and they do it more frequently as compared to other portable devices like laptops or tablets. At the same time, the prevalence of sleep problems among this population is increasing, and many link this fact to digital media use. Therefore, an adequate understanding of how smartphones interfere with adolescents’ sleep is particularly important.”

The study included 203 Czech adolescents aged 13 to 17. These participants downloaded a custom-made mobile application on their smartphones, which collected smartphone logs (including screen status) and administered short surveys for 14 consecutive days.

The study focused on five dimensions of adolescent sleep: sleep timing, duration, efficiency, quality, and daily sleepiness. Participants self-reported their sleep outcomes each morning, including sleep onset time, sleep onset latency, sleep duration, subjective sleep quality, and daily sleepiness. Smartphone use before sleep was measured objectively based on screen-on time within 2 hours before self-reported bedtime. Other covariates such as age, gender, insomnia symptoms, and use of other media devices were also considered.

Contrary to expectations, the researchers did not find significant associations between smartphone use before sleep and any of the sleep outcomes at the between-person level. The strongest predictor of sleep outcomes was the presence of insomnia symptoms, which was associated with later sleep onset time, longer sleep onset latency, shorter sleep duration, lower sleep quality, and higher daily sleepiness. Additionally, participants who typically used other media devices before sleep tended to have later sleep onset times and shorter sleep durations.

This suggests that the impact of smartphones on sleep may be more complex than previously thought. Factors such as habituation to smartphone use and physiological adaptations to screen light could play a role in mitigating the potential negative effects.

“We did not find the adverse effect of smartphone use in two hours before sleep on adolescent sleep,” Tkaczyk told PsyPost. “The findings of our study showed that adverse effects on sleep were related to the use of other digital media before bedtime and not to smartphones. Therefore, parents could consider constraining their children’s media use in the evenings. For example, the National Sleep Foundation recommends turning off electronic devices at least one hour before bedtime.”

At the within-person level, the researchers found that, on nights when adolescents used smartphones before sleep for longer than their typical use, they actually tended to get more sleep. However, these associations were relatively small.

“Interestingly, our study found that on days when adolescents used smartphones before sleep more extensively than usual, they went to bed a bit earlier and slept a bit longer,” Tkaczyk explained. “In this regard, our study showed that smartphone use before sleep may be ‘the lesser of two evils’ and that smartphones might even work as a sleep aid on some occasions.”

But the study, like all research, includes some caveats.

“It is important to reflect that our study was conducted on a relatively small and not representative sample of Czech adolescents,” Tkaczyk told PsyPost. “While convenience sampling is typical for studies based on intensive longitudinal designs, replication studies are needed to provide further evidence. At the moment, I know about two similar studies, one has also been recently published, and the other is going to be published soon, which arrived at findings similar to those of our study.”

“To get a more complex understanding of whether and how smartphone use impacts adolescents’ sleep, we now need to analytically distinguish between specific uses of smartphones in the context of sleep, for example, in terms of different content assessed (passive entertainment versus exchanging comments on SNS). We also need to consider specific response states associated with different uses of smartphones, such as psychological arousal or changes in momentary effects.”

“The disparity between our findings and some prior research reporting the adverse impact of smartphone use on adolescents may be explained to some degree by the different methodological approaches,” Tkaczyk explained. “The majority of prior findings were based on survey data. In a typical scenario, at one point in time, participants reported their typical sleep and smartphone use patterns. In our study, we took a novel approach. We used a custom-made application developed by our research team to collect objective data on how adolescents use their smartphones for 14 consecutive days.”

“Via the same app each morning, we asked adolescents participating in our study to report their sleep last night, evaluate its quality, and report their daily sleepiness. We believe such an approach provides a more valid and accurate picture of adolescents’ smartphone use and sleep. Also, it allows extend current research by taking into account the day-to-day variability in smartphone use and sleep.”

The study, “Are smartphones detrimental to adolescent sleep? An electronic diary study of evening smartphone use and sleep“, was authored by Michał Tkaczyk, David Lacko, Steriani Elavsky, Martin Tancoš, and David Smahel