Résumé
Background
Sleep problems have been associated with an increased risk of dementia. However, the period in which sleep begins to deteriorate in the natural history of dementia remains unknown. The aim was to model and compare trajectories of several sleep measurements in the 14 years prior to diagnosis of dementia in subjects with dementia and matched controls.
Method
Data were collected from a large community‐dwelling elderly cohort (3‐City‐Montpellier) at baseline and at each follow‐up. Incident cases of dementia were systematically diagnosed and validated. Repeated measures of total sleep time (TST), time in bed (TIB), wake‐up time, bedtime and, daytime sleepiness (DS) were assessed via self‐questionnaire. Based on a nested case‐control study, sleep trajectories between cases and controls were performed using latent‐process mixed models and a backward timescale.
Result
Analyses were conducted on 205 cases and 813 matched controls. TST and TIB were higher among cases during all the follow‐up with a significant faster increase in cases. For TST, mean predicted values were ‐14 years before diagnosis and at year 0 (matching visit): 6.9 [95%CI= 6.6‐7.1] and 7.2 [95%CI= 6.9‐7.4] for controls and 7.0 [95%CI= 6.6‐7.3] and 7.9 [95%CI= 7.5‐8.2] for cases. Trajectories between both groups differed from 0 to ‐8.5 years before diagnosis. Bedtime trajectories decrease significantly over time in the two groups, more strongly in cases (mean predicted values at ‐14 years before diagnosis and at year 0 were 22.8 [95%CI= 22.7‐22.9] and 22.6 [95%CI= 22.5‐22.7] for controls and 22.7 [95%CI= 22.6‐22.9] and 22.2 [95%CI= 22.0‐22.4] for cases). A significant case‐control difference from 0 to ‐8.2 years prior to diagnosis was reported. In contrast, trajectories of wake‐up time and DS remained stable over time in both groups. Still, wake‐up time trajectories crossed at about ‐5 years before diagnosis. There were no significant case‐control differences in trajectories for DS.
Conclusion
In prodromal dementia, TST and TIB increased, whereas bedtime was getting earlier and, wake‐up time and DS remained stable. Results suggest that optimal period for the management of sleep health to prevent dementia begins at least 8 years before the diagnosis of dementia.