Effects of evening smartphone use on sleep quality in adolescents and young adults

Introduction:
Smartphones have become seamlessly integrated into our daily lives and accompany us around the clock. However, smartphone screens emit blue light, which can interfere with sleep. In addition, the content we consume, especially in the hours before bedtime, may also affect the quality of our sleep.
Method:
We investigated the effects of smartphone use on subjective (sleep diary) and objective (actigraphy) sleep quality in 23 healthy male subjects (M = 18.0 years; SD = 3.38 years) over a period of 2 weeks. Smartphone use was recorded via an app (Murmuras, Germany) allowing us to analyze hourly usage times and different types of content consumed (e.g., social media). Using multilevel linear models (jamovi, version 2.3), we expected that smartphone use during the evening hours between 8pm and 11pm would negatively affect sleep quality. We also investigated whether weekends compared to work/school days would influence this relationship.
Results:
Results from actigraphy showed that higher consumption of social media (t(1166)=-2.50, p=0.013) and media/video content (t(1163.2)=-3.39, p< .001) in the evening hours was associated with less efficient sleep. For the social media category, this was particularly true on weekends (t(115.3)=-3.22, p=.001). Furthermore, higher social media use was related to more fragmented sleep (t(116.6)=2.27, p=.023), and more intensive media/video use was associated with increased sleep latencies (t(932.4)=2.13, p=.033) as well as more awakenings (t(1162.6)=2.91, p=.004). Regarding subjective sleep measures, higher social media consumption was associated with a feeling of shallower sleep (t(1144.1)=-2.12, p=.034), more nightmares (t(1152.6)=2.63, p=.009), and dizziness after sleep (t(1136.9)=1.99, p=.047) while subjects with higher media/video consumption reported more physical complaints (t(1076.2)=-2.18, p=.030), less light-heartedness (t(602.1)=2.65, p=.008) and less relaxation (t(653.1)=2.32, p=.021), especially on work/school days.
Conclusion:
Our work indicates that the negative effects of smartphone use go beyond the impairment of sleep quality caused by blue light. The type of content we consume shortly before bedtime, particularly social media and other emotionally engaging categories, also affects how well we sleep afterwards. Good sleep hygiene in terms of these usage habits may therefore be advisable.