0472 Effect of a Behavioral Insomnia Intervention on 24-Hour Rest–Activity Rhythms in Breast Cancer Survivors

Abstract Introduction Brief Behavioral Treatment for Insomnia (BBTI) improves insomnia symptoms, but its effects on 24-hour rest–activity rhythms (RAR) are not well understood. We evaluated whether BBTI improved RAR parameters compared with an attention control (AC) group among breast cancer survivors (BCS) with insomnia. Methods This secondary analysis of a randomized controlled trial of insomnia in cancer survivors was restricted to BCS who completed both baseline and 1-month actigraphy assessments (N=52; BBTI n=27, AC n=25). Participants were randomized to three weekly sessions of BBTI or an AC healthy eating program and wore a wrist-actigraph (Philips Respironics) for one week at baseline and again 1 month after treatment. Activity count data (60 second epoch) were processed using ActCR and customized function from GGIR package to derive parametric (mesor, amplitude, acrophase) and non-parametric (interdaily stability, intradaily variability, relative amplitude, most active 10-hour midpoint [M10], least active 5-hour midpoint) rest–activity metrics. Linear mixed-effects models were used to assess changes in these metrics over time by treatment group, incorporating time, treatment, and their interaction in the fixed effects portion of the models. Results Participants were, on average, 60 years old, predominantly White and married or living with a partner. Time since breast cancer diagnosis averaged 9.6 and 7.4 years in the BBTI and attention control groups, respectively. Baseline insomnia severity was in the subthreshold–moderate range (mean ISI ≈13), and there were no significant between-group differences in demographic, clinical, or insomnia characteristics. Within groups, pre- to post-treatment changes in parametric and non-parametric rest activity metrics were small in the BBTI group. In the AC group, the M10 midpoint became modestly later (~0.4 hours; d≈0.30) with other parameters largely unchanged. Between groups, no significant treatment-by-time interactions were observed for any rest–activity rhythm parameter (all p≥0.09; |d| ≤ 0.42). Conclusion In this sample of BCS with insomnia, the BBTI intervention showed no significant group or time effects in actigraphic RAR parameters compared to the AC group over the 1-month period. Larger trials with longer follow-up and interventions that more directly target sleep and circadian health may be needed to meaningfully modify RAR in this population. Support (if any) NIH/NINR R01NR018215 (Dickerson); NIH/NHLBI T32HL007953 (Kwon).