Trajectories of daytime sleepiness and their associations with dementia incidence.

Several studies have associated daytime sleepiness with risk of dementia, but it is unknown whether longstanding and emerging daytime sleepiness equally signal a risk of dementia, and whether other health factors explain these associations. In a prospective, population-based epidemiologic study, we (i) assessed associations of daytime sleepiness trajectories over 10 years with dementia incidence and (ii) examined whether selected health characteristics attenuated these associations. Using latent group-based trajectory analysis we categorized participants into three groups: (i) no daytime sleepiness (n = 959, 49.2%), (ii) emerging daytime sleepiness (n = 342, 17.5%) and (iii) persistent daytime sleepiness (n = 650, 33.3%). Compared with no daytime sleepiness, emerging and persistent daytime sleepiness were similarly associated with greater incident dementia risk (respective hazard ratios [95% confidence intervals] were 2.2 [1.3, 3.5] and 1.9 [1.2, 3.1]). Baseline blood pressure, body mass index, chronic disease diagnoses and symptoms of depression did not attenuate these associations. In contrast, lack of independence in instrumental activities of daily living attenuated the daytime sleepiness-dementia association by approximately 17%-21%. These findings suggest that persistent and emerging daytime sleepiness may signal a risk of dementia. However, the underlying mechanisms remain unclear. Further studies should investigate whether and how pathways to sleepiness, functional impairment and dementia pathophysiology interrelate and manifest together over time.