Are smartphones detrimental to adolescent sleep? An electronic diary study of evening smartphone use and sleep

Previous research associated smartphone use with worsened sleep among adolescents. However, the prior findings were mainly based on cross-sectional, self-reported data, and a between-person level of analysis. This study examined between- and within-person associations for adolescents' smartphone use and multiple sleep outcomes: sleep onset time, sleep onset latency, sleep duration, subjective sleep quality, and subjective daily sleepiness. The participants were 201 Czech adolescents (aged 13–17) who daily reported their sleep outcomes, daily stressors, and other media use for 14 consecutive days via a custom-made research app on their smartphones. The app also collected logs of the participants' smartphone use. We found that interindividual differences within the average volume of smartphone use before sleep were not associated with differences in sleep outcomes. At the within-person level, we found that, when adolescents used smartphones before sleep for longer than usual, they went to sleep earlier and slept longer. However, these two associations were weak. No other sleep outcomes were affected by the increased use of a smartphone before sleep on a given day. We found no interaction effects for age, gender, insomnia symptoms, media use, or daily stressors. However, the association between smartphone use and earlier sleep onset time was stronger on nights before a non-school day. Our findings suggest that the link between smartphone use and adolescent sleep is more complex, and not as detrimental, as claimed in some earlier studies.