Reciprocal effects between loneliness and sleep disturbances from adolescence to mid-adulthood: the HUNT study.

Study Objectives: Loneliness and sleep disturbances are prevalent and interrelated public health concerns, especially during the transition from adolescence to adulthood, a period marked by major psychological and social changes. However, less is known about their potential reciprocal relationship across development. This study examines the longitudinal, bidirectional associations between loneliness and sleep from adolescence to mid-adulthood using data from the Trøndelag Health Study (HUNT). Methods: We used data from Young-HUNT1 (1995-1997), HUNT3 (2006-2008), and HUNT4 (2017-2019), including 2185 participants (60.6% female). Loneliness and sleep were measured using harmonized items across waves. Structural equation modeling tested cross-lagged associations between loneliness and sleep, adjusting for sociodemographic and mental health covariates. Mediation analyses explored the underlying mechanisms of anxiety and depression. Results: Loneliness declined over time, while sleep showed a fluctuating pattern. Both constructs demonstrated high temporal stability. Loneliness did not significantly predict future sleep problems; however, sleep in early adulthood was a predictor of increased loneliness in midlife. Cross-sectional associations between loneliness and sleep were significant in adolescence and mid-adulthood. Mediation analyses showed that anxiety and depression mediated the longitudinal links between loneliness and sleep disturbances across different life stages. Conclusions: Loneliness and sleep are stable and interrelated across development. Sleep problems in early adulthood appear to be a stronger predictor of future loneliness, highlighting sleep as a potential intervention target to reduce long-term social and mental health difficulties. Symptoms of anxiety and depression mediated these associations, indicating key psychological pathways linking loneliness and sleep over time.