The Role of Psychological Flexibility in Health-Related Quality of Life Among Patients With Persistent Physical Symptoms Associated With Indoor Environment and Chronic Fatigue – 9-Month Follow-Up of a Randomized Controlled Trial

Background Persistent physical symptoms (PPS) can significantly impair health-related quality of life (HRQoL). Psychological flexibility (PF), characterized by the ability to adapt functionally and congruently to diverse situations based on personal values, may moderate the impairment of HRQoL. This study examined whether the intervention based on internet-delivered acceptance and commitment therapy (iACT) combined with individual case formulation and treatment as usual (TAU) ( n = 50) was effective in improving HRQoL compared to TAU alone ( n = 53) in adults with PPS associated with indoor environment and/or chronic fatigue syndrome. Then, the mediating role of PF was explored. Method In this trial (ClinicalTrials.gov NCT04532827), self-report questionnaires were administered to evaluate HRQoL, and PF, including general PF, cognitive fusion, and thought suppression. The primary outcome was HRQoL. Outcomes were assessed at baseline, at post-intervention (3 months from baseline), and at 3- and 9-month follow-ups from post-intervention. Results Significant interaction effects for HRQoL were found in the iACT + TAU group from baseline to the 9-month follow-up ( p = 0.003), indicating the HRQoL increased more in the iACT + TAU group, compared to the TAU alone ( p = 0.164). PF did not mediate the change of HRQoL during the follow-up. Conclusion The iACT + TAU combined with individual case formulation significantly increased HRQoL compared to TAU alone. However, no mediation effects were observed, suggesting that PF did not mediate the change in HRQoL. Further research on mechanisms of change is warranted to enhance understanding of both conditions and lead to more effective treatments.