Public health officials and clinicians routinely advise social media users to avoid nighttime social media use due to the perception that this delays the onset of sleep and predisposes to the health risks of insufficient sleep. The evidence behind this advice mostly derives from surveys identifying an association between self-reported social media usage and self-reported sleep patterns. In principle, these associations could alternatively be explained by users turning to social media to pass

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... time when they are otherwise having difficulty sleeping, or by the kinds of people drawn to frequent social media use, or to the offline activities in a person's life on a night of social media use and delayed sleep. To attempt to distinguish among these explanations, we leveraged estimated bedtimes from 50,000 Reddit users reported in a recent study and their 230 million posts to test whether the relationship between sleep and social media has properties suggestive of a causal relationship. We find that users are especially likely to be active on Reddit after their bedtime (and therefore awake) on nights that they posted to Reddit shortly before bedtime, especially if they posted multiple times or in high-engagement forums that night. Similarly, users are more likely to post after their bedtime on nights when they received a response from another user to one of their own old posts shortly before their own bedtime. Overall, this study lends additional support to the notion that there likely is some causal effect of evening social media use on delayed sleep onset