Associations between Psychological Flexibility–Inflexibility Spectrum Proposed by the Acceptance and Commitment Therapy and Anxiety and Insomnia Symptoms in Young Adults

Background: Anxiety and insomnia symptoms are prevalent psychiatric conditions that often co-occur. However, knowledge about the risk factors proposed by third-wave treatments such as acceptance and commitment therapy (ACT) is limited. The present study aimed to investigate associations between the six bipolar components of psychological flexibility/inflexibility and anxiety and insomnia symptoms in a young adult population. Methodology: This cross-sectional research comprised 393 students (18–34 years, 68% female) who completed the anxiety subscale of Symptom Checklist-90, Insomnia Severity Index, and Multidimensional Psychological Flexibility Inventory. Data were analyzed using Pearson’s correlation and multiple linear regression analysis. Results: There is a significant correlation between all components of psychological flexibility/inflexibility (except for acceptance/experiential avoidance) and both anxiety and insomnia. The regression models indicated that psychological flexibility/inflexibility components could significantly predict anxiety ( R 2 from 0.15 to 0.33, P < 0.001) and insomnia ( R 2 from 0.05 to 0.14, P < 0.001) symptoms. Conclusion: Psychological flexibility and inflexibility, especially the defusion–fusion spectrum, are significant predictors of anxiety and insomnia symptoms in young adults. We conclude that the constructs proposed by some third-wave therapies such as ACT potentially play a role in the psychopathology of anxiety and insomnia conditions. Future research will provide more insight into the associations between psychological flexibility/inflexibility and other psychiatric syndromes in different age groups.