Romantic Relationships and Mental Health: Investigating the Role of Self-Expansion on Depression Symptoms.

Close relationships have the potential to fundamentally alter relationship partners' self-concepts and, consequently, can impact individuals' mental health. One type of relationship-induced self-concept change is self-expansion, which describes the cognitive reorganization of the self that can occur when individuals include aspects of their partner into the self, or when they share novel and challenging activities together. In the current research, we hypothesized that greater self-expansion is associated with fewer depression symptoms. In support of this hypothesis, across four studies using cross-sectional, dyadic, daily diary, and longitudinal methodologies, we found that self-expansion was negatively associated with depressive symptoms. This association was robust and remained a significant predictor of depression symptoms when controlling for demographic factors (gender, age, relationship length; Studies 1-4) and known risk factors of depression (dysfunctional attitudes, major life stressors, self-concept clarity; Study 2). Moreover, individuals' self-expansion negatively predicted depression symptoms at the daily level (Study 3) and longitudinally over 9 months (Study 4). These results are the first to show the link between self-expansion and depression symptoms, suggesting that self-expansion may have robust benefits for individuals, beyond improving relationship dynamics.