Disrupted sleep rhythms may increase dementia risk through impaired waste clearance

Why are conditions such as chronic stress, depression, cardiovascular disease, fragmented sleep, and aging all associated with a higher risk of dementia? In a new review piece in Science, University of Rochester Medicine neuroscientist Maiken Nedergaard, MD, DMSc, proposes that many of these seemingly different conditions may converge on the same biological problem: disruption of a sleep-dependent brain rhythm that helps clear waste from the brain.

The article presents a new way of thinking about sleep, not simply as a period of rest, but as a highly organized biological state that coordinates brain chemistry, blood vessel movement, and cerebrospinal fluid flow to support the brain's nightly cleaning process. The piece also points to a potential biomarker, heart rate variability, which can already be tracked with consumer wearables, as a simple, noninvasive way to assess sleep-related brain health and identify people at increased risk for cognitive decline.

Sleep is not a quiet or inactive state. During sleep, the brain shifts into a coordinated rhythm that appears to support one of its most important housekeeping functions."

Nedergaard's lab at URochester Medicine helped transform neuroscience research in 2012 with the discovery of the glymphatic system, a brain-wide network that circulates cerebrospinal fluid through tissue surrounding blood vessels to help remove metabolic waste. The system is especially active during sleep and has since become central to research into Alzheimer's disease, Parkinson's disease, stroke, traumatic brain injury, and other neurological disorders.