Data from 715 UK infants and toddlers aged 6–36 months indicated a significant association between the frequency of touchscreen use and sleep quantity (reduced total duration, with reduced duration of night-time and increased daytime sleep), and longer sleep onset (time taken to fall asleep). Every additional hour of tablet use was associated with 15.6 minutes less total sleep (on average, 26.4 minutes less of night-time sleep and 10.8 minutes more of daytime sleep). However, we found no association between touchscreen use and the number of night awakenings. To our knowledge, this is the first study to investigate the association between touchscreen use and infant/toddler sleep. Our results are consistent with a recent meta-review in older children and adolescents illustrating the negative effects of touchscreen use on sleep quality and quantity27, extending the findings to younger children under the age of 3. Our results also extend existing reports on the negative effects of TV exposure on sleep in this age group20,21,22,23,24. We show that, independent of other known factors related to sleep and touchscreen use (age, sex, maternal education and TV exposure), touchscreen use was robustly associated with many sleep attributes.

Studies that have examined media use and sleep have hypothesized four potential mechanisms by which screen time can affect sleep in older children and adolescents. Firstly, electronic media may directly displace the time that children have available for sleep, leading to later bedtime and shorter night-time sleep duration6,7. Secondly, the content of the media may elevate psychological and physiological arousal, making it more difficult for children to fall asleep and reducing the quality of sleep28. Third, the bright blue light from screens can affect the circadian timing through melatonin suppression29,30, indirectly affecting arousal levels. Fourth, certain heritable traits in a child such as sensation seeking or hyperactivity, which correlate highly with his/her family environment, may also lead to both irregular sleep patterns and increased tablet use. As infants and toddlers have less control over their bedtime schedule, the displacement account is less likely to explain shorter sleep duration than in older children or adolescents, unless parents are, themselves inconsistent and irregular in their night-time routine. However, the portability of touchscreens does allow more flexibility in terms of where such devices are used. As such, some young children who have a touchscreen device in their bedroom may delay falling asleep in favor of playing on a touchscreen or even seek the device when restless in the night. Our finding of increased sleep latency could be due to increased physiological arousal from the media content or from the bright light. However, in the current study we are unable to confirm these hypotheses, as information on the time or nature of exposure is not available. Future research is needed to clarify this relationship by carefully documenting the time and content of use, and, if possible, also measure melatonin levels, physiological arousal and specific temperament traits.

In addition to shorter night-time sleep, increased touchscreen use was also associated with increased daytime sleep. Similarly, increased background TV exposure (not necessarily TV that the child is watching) was also independently associated with reduced daytime sleep. Recent studies in toddlers suggest that daytime nap duration is negatively correlated with night-time sleep duration and sleep onset31. As such, touchscreen use may indirectly influence daytime sleep duration by reducing night-time sleep quality, or vice versa. This hypothesis would also be consistent with studies in older children, which found increased media use affecting daytime functioning due to indirect effects of poor quality and quantity of night-time sleep32. However, unlike school children, infants and toddlers regularly nap in the day. Thus, the indirect impact of media use on emotional and cognitive functioning through sleep might be lessened in this younger age group, as they are able to ‘catch up’ with their sleep during the day. Our findings indicate that this may not be the case, as despite on average sleeping more during the day, infants and toddlers who spend more time on a touchscreen still spend less overall time sleeping. Future studies that examine the impact of media use on developmental outcomes in this younger age group should take into account both daytime and night-time sleep duration. In addition to the quantity of sleep, Nakagawa and colleagues also reported an association between day time naps that occurred during late afternoon and shorter night-time sleep duration and late sleep onset time31. The extent to which increased touchscreen use affects timing of daytime naps cannot be determined in the present study, but warrants further investigation.

Sleep fragmentation, as measured by the number of night awakenings, was not associated with touchscreen use in the current study, when controlling for the known confounds. Previous studies in older children and adolescents that included this variable have reported mixed results: while one study found a positive association between media use and self-report night-time awakenings in adolescents33, another study in younger children aged between 4 and 10 years did not34. However, sleep fragmentation in the previous and current study was based on self or parent-report, which may not be reliable. A recent study in infants using both parent-report and an objective actigraphy measure of sleep revealed a weak association between the two measures for the frequency of night awakening (r = 0.10), but a strong correlation for nocturnal sleep duration (r = 0.43)35. Furthermore, the objective measure of sleep fragmentation was also found to have the strongest impact on infant cognitive development35. Although we did not find an association between touchscreen use and sleep quality, this could be due to an underestimation of night awakenings by parent report. It is important that future studies also include an objective measure of sleep fragmentation, either using actigraphy or EEG measures.

In this study, we included a range of specific sleep outcomes encompassing quality, quantity and onset of sleep. Our findings extend the limited knowledge at present on media use and sleep in toddlers beyond TV exposure. Yet, a few limitations should be noted. Firstly, our findings are based on cross-sectional data, therefore a directional relationship between touchscreen use and sleep cannot be established. It is possible that infants and toddlers who use touchscreen devices more frequently also require less sleep. Future longitudinal or intervention studies will be needed to examine the direction of causality. Secondly, as mentioned above, we did not include specific records of the timing, content and location of use. Such information would be crucial in future studies to elucidate the mechanisms by which touchscreen usage impacts sleep patterns. Previous studies in older children do suggest, however, that it is not the exposure to a media device per se that impacts sleep, but the modifiable aspects of media such as content, timing and environment that may have a damaging effect on sleep24. Third, the current study only investigated the association between touchscreen use and sleep, it will be important for future studies to establish whether this reduced sleep indirectly impacts cognitive functioning. It is worth noting that touchscreen use may also have positive effect on some aspects of development. In our recent study of the same sample of infants and toddlers, increased active touchscreen use was associated with earlier achievement in fine motor milestones12. Thus, total restriction of touchscreen use may limit young children in terms of the potential benefits of these devices. Together, our findings emphasize the need for a more in-depth understanding of how to maximize benefits and minimize negative consequences of this modern technology.