Adam Spira and others from Hopkins studied 128 patients prospectively for sleepiness and presence of amyloid-beta 16years later. Those with Excessive Daytime Sleepiness and Napping were 3 times more likely to have amyloid deposits.

Beta-Amyloid deposits are linked to Alzheimer's Dementia. These were detected using Pittsburgh Compound B Positron Emission Tomography (PiB PET) scans.

This supports the link of chronic sleepiness as a risk factor for cognitive decline.

https://academic.oup.com/sleep/search-results?page=1&q=adam+spira&fl_SiteID=5573&SearchSourceType=1&allJournals=1

https://hub.jhu.edu/2018/09/06/excessive-sleepiness-alzheimers-disease/