IntroductionAmidst the COVID-19 pandemic, widespread feelings of social isolation have become more prevalent than ever before as lockdowns and social distancing measures led people to remain in their homes. The constructs of social isolation and loneliness are similar but reflect slightly different aspects of social experience. Social isolation reflects the amount of social contact a person experiences, whereas loneliness reflects the subjective experience of an emotional yearning for such contact. While is known that sleep problems have increased during the pandemic, there has been little research into the potential effects of social isolation on sleep problems. Here, we examined the influence of social isolation on the extent to which insomnia has interfered with daily life activities. We hypothesized that social isolation would contribute to greater disruption in daily functioning from insomnia, exclusive of the effects of loneliness.Methods13,298 English-speaking adults from across the U.S. (18-92 years old; 57.5% female) completed an online battery of assessments that included demographic questions, the Insomnia Severity Index (ISI), and the UCLA Loneliness Scale – Version 3 between April 2020 and April 2021. Participants were grouped based on whether they felt “socially isolated” or not at the time of assessment. Social isolation groups were compared for the extent that insomnia interfered with daily functioning, while statistically controlling for loneliness.ResultsAfter controlling for loneliness, socially isolated individuals reported much greater daily interference from sleep problems, M=1.58, SD=1.19, compared to those who denied feeling socially isolated, M=0.96, SD=1.04, F(1,13295)=287.67, p=7.5x10-64.ConclusionSocial isolation during the pandemic was associated with significantly greater disruption of daily functioning due to sleep-related issues, even after adjusting for self-reported loneliness. Thus, feeling isolated and lacking social contact was related to functional degradation due to sleep problems. Prior evidence suggests that social isolation can have a dramatic negative impact on mental health and can lead to increased all-cause mortality, but these results suggest social isolation may also impact sleep health and functional outcomes (whether that be physical, cognitive, or psychological). Thus, being isolated during the pandemic was associated with greater degradation of functional outcomes of sleep, regardless of subjective loneliness.Support (If Any)