Improvements in daytime sleep-related repetitive negative thinking, bedtime general repetitive negative thinking, and activity levels were associated with the degree to which depressive symptoms improved among individuals receiving CBT-I.
Participants receiving CBT-I exhibited clinically significant reductions in depressive symptoms across the study period.
Participants showed improvements in both general and sleep-related repetitive negative thinking (RNT) during daytime and bedtime over the course of CBT-I.
Participants showed a boost in activity levels (improved behavioural activation) during CBT-I.
Improvement rates in daytime sleep-related RNT and bedtime general RNT were strongly associated with the degree to which depressive symptoms improved.
Improvement rates in activity levels were moderately associated with the rate at which depressive symptoms improved.
Not all forms of RNT were equally associated with depression outcomes, with the pattern suggesting that RNT conceptually or temporally linked to insomnia is most relevant.
The authors characterise the findings as preliminary and call for causal experimental designs to investigate these factors as potential mechanisms of change.
This research suggests that when people undergo Cognitive Behavioural Therapy for Insomnia (CBT-I), specific patterns of change in their thinking habits and activity levels are linked to how much their depression improves. The study followed 88 adults through CBT-I treatment, measuring their repetitive negative thinking (a tendency to dwell on worries and problems) in different contexts — during the day, at bedtime, about sleep specifically, and about general life concerns — as well as their overall activity levels. On average, participants showed meaningful reductions in both insomnia and depression symptoms, as well as improvements in these cognitive and behavioural factors. The most notable finding was that two specific types of repetitive negative thinking were strongly linked to depression improvement: worrying about sleep during the daytime (daytime sleep-related RNT) and general worrying that happens at bedtime (bedtime general RNT). Improvements in physical activity levels were also moderately linked to depression improvement. Interestingly, general daytime worrying and sleep-specific worrying at bedtime were not highlighted as strongly connected to depression outcomes, suggesting that it is thinking patterns that overlap with the insomnia experience — either by topic (sleep-related) or by timing (at bedtime) — that matter most for depression recovery during this treatment. This research matters because CBT-I is already recommended as the first-line treatment for insomnia, and these findings help explain why it also tends to reduce depression. If replicated with stronger study designs, this could inform how CBT-I is delivered or enhanced — for example, by paying particular attention to helping patients reduce sleep-focused daytime worry and general bedtime rumination, and by encouraging more activity. The authors caution that these are preliminary findings and that future studies using experimental methods are needed to confirm whether these factors actually cause depression to improve, rather than simply changing alongside it.
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Upload Your LabsLall V, Ree M, Bucks R. (2026). Cognitive and behavioural factors associated with improvements in depression outcomes among individuals attending CBT for insomnia.. Behaviour research and therapy. https://doi.org/10.1016/j.brat.2026.105146