Health vulnerability and loneliness among adolescent and young adult populations: a comparison of generations based on a nationwide survey in Japan

Introduction Using nationally representative data, we investigated differences in loneliness across generations in Japan, focusing on the unique factors affecting adolescents and young adults.Methods We analysed data from the 2022 and 2023 Basic Survey on Human Connection conducted by the Japanese Government. The dataset included responses from 22 361 individuals aged 16 years and older. Loneliness was assessed using the three-item University of California at Los Angeles Loneliness Scale (UCLA-LS). Multiple linear regression models adjusted for sociodemographic characteristics, social and health-related variables were employed to identify the predictors of loneliness across age groups. Interaction terms between age group and explanatory variables were included to assess whether these associations differed across generations.Results Adolescents and young adults, as well as middle-aged adults, reported greater loneliness than older adults (mean UCLA-LS scores: 6.80, 6.84 and 6.29, respectively; p<0.001). Significant loneliness predictors included a lack of confidants, poor self-rated overall health, low life satisfaction, anxiety and non-participation in social activities. Interaction analysis demonstrated that the association between poor health and loneliness was significantly stronger in adolescents and young adults than in older adults (β=0.80, 95% CI 0.57 to 1.04; false discovery rate-adjusted p<0.001). In addition, the associations of anxiety and unemployment with loneliness were stronger among working-age populations than among older adults. These findings suggest age-related differences in the factors associated with loneliness.Conclusion Loneliness among adolescents and young adults appears to be more strongly associated with health vulnerability, whereas psychosocial and economic factors were more strongly associated with loneliness in working-age populations. These findings highlight the importance of developing age-specific strategies to reduce loneliness, particularly among younger individuals experiencing poor health.