LAUSR

Recent evidence suggests that older adults with more frequent and longer daytime naps have an increased risk of Alzheimer’s dementia (AD). We aim to further elucidate whether the timing of daytime napping impacts AD risk. Data were from 1,203 participants in the Rush Memory and Aging Project (mean age at actigraphy=80.85±7.30; 77% female). Each participant wore an accelerometer (Actical) for up to 14 (mean 9.57±1.17) days and have been followed for up to 17 (mean 6.92±4.12) years with annual clinical assessment to determine AD status. We used a validated algorithm to identify daytime nap episodes between 9am-7pm and determined the timing of naps based on the midpoint of each nap. We computed the proportion of naps within each 2-h window for each participant, i.e., morning (9-11am), noon (11am-1pm), early afternoon (1-3pm), late afternoon (3-5pm), and early evening (5-7pm). Cox proportional hazards models were performed to examine the associations of napping timing with risk of AD, with adjustment for age, sex, education years, and nighttime sleep duration. Among all participants, 357 (30%) developed AD during the follow-up (mean time to AD: 6.34±3.98 years). Taking all naps in the morning, compared to taking all naps at other times, is associated with a 1.9-fold increased AD risk (HR [95%CI]=1.93[1.002-3.58], p=0.04). This association was only observed in women (HR=2.22[1.08-4.38], p=0.03) but not in men (HR=1.01[0.18-4.38], p=0.99). Moreover, the association between naps in the morning and AD risk was attenuated when additionally adjusted for total nap duration and frequency, BMI, and intradaily variability in rhythms (HR=1.71[0.85-3.43], p=0.13). The proportions of naps during other times of the day were not associated with AD risk (noon: HR=1.02[0.44-2.23]; early afternoon: HR=1.28[0.72-2.22]; late afternoon: HR=0.62[0.33-1.15]; early evening: HR=0.62[0.30-1.25]; ps>0.05). More naps in the morning were associated with an elevated risk of developing AD in older adults. A higher propensity of napping in the morning may be an indicator of disturbances in sleep-wake regulation. Future studies are warranted to test whether interventions to consolidate nap timing or limit napping in the morning can improve neurocognitive outcomes. Alzheimer’s Association (AARFD-22-928372), NIA (R01AG17917), NIH (RF1AG064312), BrightFocus Foundation (A2020886S).