The growing prevalence of smartphones in adolescents' daily lives have raised concerns about their adverse effects on sleep. 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 of particular importance.
In our research, we used a sample of 201 Czech adolescents aged 13 and 17 to examine how time spent using a smartphone within 2 hours before bedtime is associated to sleep onset time, sleep latency, sleep duration and quality, and daytime sleepiness. We distinguished between effects related to typical patterns of smartphone use before sleep and effects related to day-to-day variability in smartphone use. The former may be understood as differences in sleep outcomes between adolescents who on average use smartphones before sleep for shorter time or occasionally as compared to adolescents who use it extensively. In the latter case, we were interested in change in sleep related to time spend using smartphone on a given day as compared to typical level of use for each participant. For example, whether occasional extensive use of smartphone before sleep is associated to worsened sleep on that night.
We did not found the association between typical patterns of smartphone use before sleep and sleep. However, other media use before sleep was associated with worsened sleep meaning that adolescents who typically use other digital media before sleep more extensively reported later sleep onset and shorter sleep duration as compared to those who used it less extensively.
Concerning effects related to day-to-day variability in smartphone use we 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. It's a rather surprising finding suggesting that on some occasions some adolescents may use smartphones as a sleep aids. In line with, the mood management theory, consuming calm and relaxing media content before sleep may result in the alleviation of the initial level of arousal, stress, and negative affect and, in consequence, it may facilitate earlier sleep onset and longer sleep duration which is the association that we found in our data. However, this hypothesis need to be verified in future studies. As for the usage of other media, we found that on days when adolescents used other media before sleep more extensively as compared to their typical use, it took them less time to fall asleep but they went to sleep later as compared to their typical sleep routine.
So what does the result of our study mean for parents who are concerned about how smartphones impact their children's sleep? In light of our findings, adverse effects on sleep were related to use of other media before sleep and not to smartphones. Also other studies found the adverse association between using screen media before sleep and sleep quantity and quality. 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.
Our findings however showed that use of smartphone before sleep may be “the lesser of two evils” and that on some occasions smartphones might even work as a sleep aid. One possible explanation why we did not find smartphone use to be detrimental to adolescent sleep is relatively small screen size. It was found experimentally that the screens of smartphones and tablets are not large enough to reach the 50-lx light exposure level, which is considered the critical threshold for inducing circadian phase shifts. Moreover, because smartphones are very small and portable there are often used in bed and, for normal sleepers, there are strong cues for sleep associated with their beds.
Finally, the disparity between our findings and some prior research reporting adverse impact of smartphone use on adolescents may be explained to some degree by the different methodological approach. Majority of prior findings on associations between smartphone use on adolescent sleep is based on survey data. In typical scenario, at one point in time participants report retrospectively their typical sleep and smartphone use patterns. Such approach is prone to bias and inaccuracy related to factors such as recall, memory, or social desirability of answers. In our study, we took a novel approach. We used custom made application developed by our research team to collect objective data on how adolescent use their smartphones for 14 consecutive days. Via the same app on each morning we asked adolescent participating in our study to report their sleep last night, evaluate its quality and report their daily sleepiness. We believe that such approach provide much more valid and accurate picture of actual adolescents smartphone use and sleep.
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