Abstract
To effectively tackle loneliness in youth, prevention and intervention strategies should be based on solid evidence regarding risk and protective factors in this age group. This systematic literature review identifies and narratively synthesizes longitudinal studies of risk and protective factors for loneliness in children and adolescents aged below 25 years. A systematic literature search was conducted in October 2023 using PsycINFO and MEDLINE, resulting in n = 398 articles, with n = 105 articles meeting the inclusion criteria. The examined factors included demographic (e.g., gender), socioeconomic (e.g., income sufficiency), social (e.g., peer acceptance), mental health (e.g., depression), physical health (e.g., disabilities), health behavior (e.g., sport participation), and psychological factors (e.g., shyness). Additionally, adverse childhood experiences (e.g., child maltreatment) and environmental factors (e.g., neighborhood characteristics) were investigated. Despite the wide range of potential risk and protective factors examined, relatively few studies provided strong evidence for a prospective association with loneliness. Risk factors that were consistently identified across multiple longitudinal studies included low peer acceptance and peer victimization, depression, social anxiety, internalizing symptoms, low self-esteem, shyness, and neuroticism. Additional replication is required to evaluate factors that have shown significant associations with loneliness in only a limited number of longitudinal studies (e.g., aggression).