堀越 勝

BACKGROUND: Major depression is a common and disabling disorder, and individuals with subthreshold depression represent a key at-risk group. We previously demonstrated that specific cognitive behavioural therapy (CBT) skills training delivered via a smartphone app (behavioural activation, cognitive restructuring, problem solving, assertion training and behavioural therapy for insomnia) improved depressive symptoms for up to 26 weeks. AIMS: To evaluate the long-term effects (up to 50 weeks) of CBT skills and their combinations for preventing major depressive episodes and reducing the total burden of depression (TBD). METHOD: Participants were adults from the general population with subthreshold depression. A master protocol trial with four 2 × 2 factorial trials was used to randomise 3280 participants to one of nine intervention arms or a self-check control group. The primary outcome was time to onset of major depression by week 50. RESULTS: Hazard ratios for the interventions ranged from 0.52 (95% CI: 0.29-0.94) to 0.63 (95% CI: 0.36-1.10), with behavioural activation + assertion training showing the greatest preventive effect (number needed to treat: 23.3 (95% CI: 12.2 to 250)), followed by behavioural therapy for insomnia, behavioural activation + behavioural therapy for insomnia and cognitive restructuring. All interventions reduced TBD scores compared with control, with behavioural activation + cognitive restructuring exhibiting the largest reduction. Effect sizes at week 50 ranged from -0.34 to -0.07 and behavioural activation + cognitive restructuring was the most effective. No serious adverse events were reported. CONCLUSIONS: The current findings indicated that specific CBT skills - particularly behavioural activation +assertion training , behavioural activation + cognitive restructuring and behavioural therapy for insomnia - effectively prevented the onset of depression and reduced the TBD at 50 weeks. Given its brevity, portability, accessibility and scalability, smartphone-based CBT is promising as a preventive intervention.

Abstract Background Smartphone-based cognitive behavioral therapy (CBT) programs offer accessible interventions for subthreshold depression, yet engagement needed for meaningful benefit remains unclear. We examined how lesson and worksheet engagement relate to depressive symptom improvements in a behavioral activation (BA) intervention, accounting for time-varying confounders. Methods This secondary analysis included 298 adults assigned to the BA arm of the RESiLIENT trial, a randomized controlled trial in Japan. Lesson and worksheet completion were treated as time-varying exposures, each yielding four engagement patterns: minimal (Few-Few) , early (Many-Few) , late (Few-Many) , and consistently high (Many-Many). Outcomes were depressive symptom changes measured by the Patient Health Questionnaire-9 (PHQ-9) at weeks 6 and 26. We applied the parametric g-formula to estimate counterfactual PHQ-9 changes under each pattern, adjusting for baseline and time-varying confounders. Results Early lesson engagement during weeks 0–3 was associated with larger PHQ-9 reductions at both weeks 6 and 26, even when later engagement declined ( Many-Few vs. Few-Few : week 6: −1.47 [95% CI −2.52 to −0.53]; week 26: −1.27 [−2.53 to −0.17]). In contrast, higher worksheet engagement was linked to improved PHQ-9 at week 6, with maximal benefit among consistently high engagers ( Many-Many vs. Few-Few : −1.25 [−2.17 to −0.44]) and late engagers ( Few-Many vs. Few-Few : −1.18 [−2.20 to −0.08]), but not persist to week 26. Conclusions Greater engagement with smartphone-delivered BA is associated with larger symptom reductions. Early lesson engagement drives sustained benefit, whereas worksheet engagement did not persist. These findings may guide digital CBT design by emphasizing early lesson completion alongside concurrent skill practice.