Chronic stress, depression, cardiovascular disease, fragmented sleep and aging all raise the risk of dementia, and in a new review published in Science, University of Rochester Medicine neuroscientist Maiken Nedergaard, MD, DMSc, proposes a reason why these very different conditions share the same endpoint. Her argument is that they converge on a single biological failure: disruption of a sleep-dependent brain rhythm that drives the removal of waste from brain tissue.
The review reframes sleep as an actively organized state rather than downtime. According to Nedergaard, sleep coordinates brain chemistry, the movement of blood vessels, and the flow of cerebrospinal fluid so that the brain can carry out its nightly cleaning. "Sleep is not a quiet or inactive state," she writes, describing a coordinated rhythm that supports one of the brain's most important housekeeping functions.
The idea builds on work from Nedergaard's own lab, which in 2012 described the glymphatic system - a brain-wide network that circulates cerebrospinal fluid through the tissue surrounding blood vessels to flush out metabolic waste. That system runs at its highest capacity during sleep, and it has since become a focus of research into Alzheimer's disease, Parkinson's disease, stroke and traumatic brain injury.
For clinical purposes, the review points to a practical hook: heart rate variability, a measure already captured by consumer wearables, as a possible noninvasive marker of sleep-related brain health that could help flag people at elevated risk of cognitive decline. That remains a proposal rather than a validated screening tool, but it suggests a route to studying glymphatic function in large populations without imaging or spinal fluid sampling.