A study published online on Aug. 30, 2021, in JAMA Neurology reveals that getting too much or too little sleep can harm your brain and cause memory and thinking problems. More than 4,400 older men and women from around the world had their brain imaging, cognitive test scores, and self-reported sleep habits evaluated by researchers. Short sleep was linked to decreased cognition, particularly in memory, as well as an increase in amyloid-beta, a protein that can form brain plaque and is a hallmark of Alzheimer's disease. The long sleep of nine hours or more has also been associated with cognitive issues, particularly in decision-making. In comparison to persons who had seven or eight hours of sleep, both short and lengthy sleep were linked to a higher BMI (a measurement of body fat), more depressive symptoms, and more napping. Although the study was observational and cannot prove causation, the findings are consistent with numerous other studies that show that too little — or maybe too much — sleep affects cognitive impairments.