Data from 70 older adults (average age 76) in the Baltimore Longitudinal Study of Aging has found that those who reported poorer sleep (shorter sleep duration and lower sleep quality) showed a greater buildup of amyloid-beta plaques.

http://www.eurekalert.org/pub_releases/2013-10/tjnj-lsa101813.php

[3606] Spira, A. P., Gamaldo A. A., An Y., & et al
(2013).  Self-reported sleep and β-amyloid deposition in community-dwelling older adults.
JAMA Neurology. 70(12), 1537 - 1543.