Cognitive and behavioural factors associated with improvements in depression outcomes among individuals attending CBT for insomnia.

Cognitive behavioural therapy for insomnia (CBT-I) is the gold-standard insomnia treatment, which also produces medium-to-large antidepressant effects at a group level. However, not everyone benefits equally and CBT-I related factors associated with varying depression outcomes are not well understood, limiting the capacity for treatment optimisation and uptake of CBT-I in routine care. This study examined whether trajectories of change in daytime and bedtime general repetitive negative thinking (RNT), daytime and bedtime sleep-related RNT, and low activity levels (improved behavioural activation) were related to the degree to which depressive symptoms improve among individuals receiving CBT-I. Eighty-eight adults (72% females) participated. Data collected at baseline, post-intervention, and 12-week follow-up were analysed using latent growth curve modelling. Participants exhibited clinically significant reductions in depressive symptoms and improvements in both general and sleep-related RNT during daytime and bedtime, along with a boost in activity levels. Moreover, improvement rates in daytime sleep-related RNT and bedtime general RNT were strongly associated with the degree to which depressive symptoms improved, while improvement rates in activity levels were moderately associated with the rate at which depressive symptoms improved. Current preliminary findings suggest that improvements in RNT that is related to insomnia, either conceptually (daytime sleep-related RNT) or temporally, (bedtime general RNT), and improvements in activity levels may be associated with the extent to which depression outcomes improve following CBT-I. This highlights the need for further investigation of these factors as potential mechanisms of change influencing depressive symptoms, using causal experimental designs.