Sibling relationships as a mediator and a moderator between parental attachment and depression among adolescents.

Depression threatens adolescents' psychological health and is influenced by negative interpersonal relationships. Previous studies have explored the effect of a negative parent-child relationship on adolescent depression but have ignored the frequent coexistence of these relationships with other family relationships, for example, sibling relationships. This study examined how parent-child and sibling relationships co-impact adolescent depression, by testing the mediating and moderating roles of sibling relationships between parental attachment and adolescent depression. A sample of 5,896 adolescents completed the Inventory of Parent and Peer Attachment, Sibling Relationship Questionnaire, and the Patient Health Questionnaire. 3,054 participants (1,506 girls) were included in the analysis (mean age = 13.70 ± 0.77 years). We found that the level of parental attachment security was negatively associated with adolescent depression, and sibling relationships not only mediated but also moderated this association. Regarding the moderating effect, only one dimension of sibling relationships (warmth) showed a significant moderating role. Specifically, sibling warmth buffered the negative association between maternal (but not paternal) attachment security and adolescent depression. Our results suggest that both negative parent-child and sibling relationships are possible risk factors for adolescent depression, and a positive sibling relationship can be a protective factor against the effect of negative parent-child relationships on adolescent depression. The present study also provides new insights for interventions adolescent depression. Sibling relationships deserve more attention in future research.