Poor & short duration sleep i.e. less than 7 hours per night & mid-life onset obstructive sleep apnoea [severe] are linked to increase risk of AD, poor cognition and memory.
Lutsey PL, Misialek JR, Mosley TH, Gottesman RF, Punjabi NM, Shahar E, MacLehose R, Ogilvie RP, Knopman D, Alonso A. Sleep characteristics and risk of dementia and Alzheimer’s disease: The Atherosclerosis Risk in Communities Study. Alzheimers Dement. 2017 Jul 21. pii: S1552-5260(17)32522-0. doi: 10.1016/j.jalz.2017.06.2269. https://www.ncbi.nlm.nih.gov/pubmed/28738188