Is digital cognitive behavioural therapy for insomnia effective in treating sub-threshold insomnia: a pilot RCT

Objective/Background: Many patients find cognitive behavioral therapy for insomnia (CBT-I) useful. However, it is currently unknown if those with sub-threshold insomnia also benefit. Here we assessed whether CBT-I is both feasible and acceptable in participants with sub-threshold insomnia. The primary aims were to evaluate participation rates and treatment acceptability, and to establish an effect size for symptom improvement. Patients/Methods: A total of 199 female participants (M_age 20 ± 5 years) took part. Following baseline assessments, participants were randomly allocated to either a six-week digital CBT-I intervention or a six-week control group receiving puzzles. Additional assessments were performed three-weeks, six-weeks, and six-months later. Results: Participation rates at each survey assessment wave did not differ between the groups (ps > 0.140), though adherence to completing each weekly task was lower in the CBT-I group, p = 0.02. Treatment acceptability was high (M (SD) = 33.61 (4.82), theoretical range 6–42). The CBT-I group showed greater improvement in insomnia symptoms at the end of the intervention compared to the control group (p = 0.013, d = 0.42), with significant variation in outcome (M = 4.69, SD = 5.41). Sub-threshold participants showed a similar pattern of results, whilst those meeting insomnia criteria showed a smaller between-group difference. CBT-I led to improvements in anxiety, paranoia and perceived stress between baseline and end of intervention. Changes in insomnia symptoms were mediated by cognitions about sleep and somatic pre-sleep arousal. Conclusions: CBT-I provides a benefit even in sub-threshold insomnia. CBT-I may be useful to tackle insomnia symptoms even when they are sub-threshold.