0096 Longitudinal Rest-Activity Rhythms Are Associated with Cognitive Trajectories and Clinical Outcomes in Older Adults

Abstract Introduction Altered circadian rhythms have been implicated in cognitive health, and 24-hour actigraphic rest-activity rhythms (RARs) are commonly used as estimates of circadian rhythmicity. Prior work has mostly examined only baseline RARs, so it remains uncertain whether mean RAR parameters or their changes over time are associated with cognitive trajectories or incident mild cognitive impairment (MCI). Methods We studied 169 cognitively unimpaired adults (71.1 8.7 years) in the BIOCARD study with wrist-actigraphy data; 137 completed 2–4 follow-up visits over 2–8 years. RAR metrics included relative amplitude (RA; day–night activity contrast), interdaily stability (IS; day-to-day regularity), and intradaily variability (IV; within-day fragmentation). Each metric was decomposed into between-person mean levels (reflecting participants’ average RAR across visits) and time-varying changes (capturing visit-to-visit deviations from each participant’s mean). Linear mixed-effects models examined associations of both mean levels and time-varying changes with longitudinal executive function, adjusting for age, sex, education, APOE-ε4 status, vascular risk, valid actigraphy days, and time since baseline, with random intercepts for participants. Exploratory Cox proportional hazards models assessed associations with time to incident MCI (n=12), incorporating both mean parameters and time-varying changes. Results Participants with higher mean RA, greater IS, and lower IV across follow-up had better executive function (RA B= 0.102, p < 0.001; IS B = 0.079, p = 0.014; IV B = −0.067, p = 0.035). Time-varying reductions in RA and increases in IV were associated with concurrent decrements in executive function (RA B = 0.023, p = 0.004; IV B = −0.019, p = 0.026). In the exploratory Cox model, higher mean RA was associated with lower MCI risk (HR = 0.499, p = 0.004), whereas time-varying changes in RA, IS, or IV were not significantly associated with MCI. Conclusion Both mean and time-varying changes in RAR parameters were associated with executive function, with stronger, more regular, and less fragmented rhythms linked to better performance. Higher mean RA was also associated with lower MCI risk. These findings highlight RARs as markers of or contributors to cognitive health and suggest that longitudinal monitoring can provide insight into cognitive resilience in older adults. Support (if any)