Investigating the interplay of loneliness and social isolation across adolescence: Findings from a nationally representative longitudinal study.

While loneliness and social isolation are risk factors for poor health and functioning, prominent theories suggest that loneliness may serve an adaptive function by encouraging social reconnection. Nevertheless, few studies have examined how loneliness and isolation relate to each other, and other outcomes, over time. Using the Environmental Risk Longitudinal Twin Study, a UK population-representative cohort of 2,232 individuals born in 1994-1995 (49% male, 90% White), we investigated how loneliness and isolation are related across time and jointly influence outcomes. Loneliness and isolation were assessed at ages 12 and 18. Mental health, well-being, health behaviors, and socioeconomic outcomes were measured at age 18. Loneliness and isolation were concurrently and longitudinally associated with each other across adolescence. Loneliness marginally moderated the stability of social isolation from age-12 to 18 (β = ‒0.08, p = 0.08) but did not observe a buffering effect, with isolated children who experienced loneliness experiencing high isolation in young adulthood. Age-12 loneliness and isolation were independently associated with poorer mental health, well-being, and socioeconomic outcomes (β = ‒0.18-0.10, p < 0.05), though experiencing both was not associated with worse outcomes. Our findings underline the pervasive impacts of childhood loneliness and isolation and challenge the view that loneliness drives social reconnection in early life.