Predictors of chronic loneliness during adolescence: a population-based cohort study.

Background: Adolescent loneliness is a growing public health issue owing to its adverse health impact. Although adolescent loneliness is common, its trajectories can show distinct patterns over time. However, there is limited knowledge regarding their determinants, particularly for chronic loneliness. We aimed to determine the predictors of loneliness trajectories across early-to-mid adolescence and examine their association with later suicidality.

Methods: Data were collected from 3165 participants from the population-based Tokyo Teen Cohort. Participants reported their loneliness at 10, 12, 14, and 16 years. Loneliness trajectories were identified using latent class growth analysis. We examined the predictive role of bullying victimization and parental psychological distress at age 10 via a multinomial logistic regression. Sociodemographic and child-related factors (i.e., chronic health conditions and cognitive delay) were included as covariates. The association between the trajectories, self-harm, and suicidal ideation by age 16 was investigated using Poisson regression.

Results: Four trajectories were identified: "consistently low" (2448, 77.3%), "moderate-decreasing" (185, 5.8%), "moderate-increasing" (508, 16.1%), and "consistently high" (24, 0.8%). Taking "consistently low" as a reference, experiences of bullying victimization predicted all the remaining trajectories [adjusted relative risk ratio 1.64, 95% confidence interval (CI) 1.18-2.28 for "moderate-decreasing," 1.88, 1.52-2.33 for "moderate-increasing," and 4.57, 1.97-10.59 for "consistently high"]. Parental psychological distress predicted the "moderate-increasing" (1.84, 1.25-2.71) and "consistently high" (5.07, 1.78-14.42) trajectories. The "consistently high" trajectory showed the greatest risk for self-harm and suicidal ideation (adjusted relative risk ratio 6.01, 95% CI 4.40-8.22; 2.48, 1.82-3.37, respectively); however, the "moderate-increasing" and "moderate-decreasing" trajectories were also at increased risk (moderate-increasing: 2.71, 2.23-3.30 for self-harm, 1.93, 1.69-2.19 for suicidal ideation; moderate-decreasing: 2.49, 1.91-3.26 for self-harm, 1.59, 1.33-1.91 for suicidal ideation).

Conclusions: Bullying victimization and parental psychological distress at age 10 were independent determinants of increased and chronic loneliness trajectories across early-to-mid adolescence. Compared with "consistently low," all other loneliness trajectories were associated with an increased risk of adolescent suicidality. Interventions targeting adolescent loneliness should include approaches to mitigate bullying and parental psychological distress. These strategies may help prevent adolescent suicidality.