Psychological flexibility as a mechanism of change in online ACT among adults living with chronic health conditions.

Living with a chronic health condition (CHC) can negatively impact quality of life (QoL) through a complex interaction of mental health challenges, functional limitations, and disease management demands. Acceptance and Commitment Therapy (ACT) is a transdiagnostic approach that shows promise in addressing shared challenges across various CHCs by fostering psychological flexibility (PF). PF has been associated with improved QoL and functional outcomes and reduced psychological symptoms in individuals living with specific CHCs; yet its mediating role in these outcomes remains underexplored. This secondary analysis examined whether changes in PF mediated improvements in QoL, psychological symptoms, and functional impairment among individuals with various CHCs. Participants (n = 100) were randomized to a six-session self-guided, online ACT program or a waitlist control group. Outcomes were assessed at baseline, post-treatment, and four-week follow-up. Results revealed that increases in PF significantly mediated improvements in QoL, with indirect effects indicating that higher PF at post-treatment predicted better QoL at follow-up. The ACT group demonstrated significant reductions in functional impairment at follow-up compared to the waitlist group, though this effect was not mediated by changes in PF. Improvements in psychological symptoms were not statistically significant and were not mediated by PF. These findings suggest that ACT effectively enhances PF, which subsequently improves QoL in individuals with CHCs. This supports the transdiagnostic applicability of ACT for improving mental health and QoL across diverse chronic conditions. Future research should explore additional mechanisms underlying ACT's effects and investigate ways to optimize its impact on functional and psychological outcomes within CHCs.