Researchers have long known that conditions such as depression, cardiovascular disease, disrupted sleep and chronic stress are linked to a higher risk of dementia. What has remained unclear is why such different conditions appear to produce similar outcomes in brain health.
The new review suggests the answer may lie in sleep-dependent brain rhythms that help coordinate the brain's nightly maintenance work, reports tekniikanmaailma.fi.
Rather than being a passive period of rest, sleep appears to be a highly organised biological state in which brain chemistry, blood vessel activity and fluid movement work together to support brain function.
The brain's night shift
At the centre of the theory is the glymphatic system, a network discovered by Nedergaard's research team in 2012. The system helps clear metabolic waste from the brain by circulating cerebrospinal fluid through brain tissue.
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Scientists say the process becomes particularly active during sleep, helping remove substances that can accumulate over time.
The latest review focuses on chemical messengers in the brain that regulate attention, mood and learning during wakefulness. During deep non-REM sleep, these systems begin operating in synchronised slow rhythms that are linked to changes in brain activity, breathing, heart rate and blood vessel movement.
Why it matters
Researchers believe these coordinated rhythms help drive fluid through the brain, allowing waste products to be cleared more efficiently.
Among the substances removed are proteins associated with Alzheimer's disease and other forms of dementia. If the process becomes disrupted, the brain may gradually lose some of its ability to eliminate harmful waste.
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The review suggests that ageing, poor sleep, psychiatric conditions, cardiovascular disease and certain medications may all interfere with these critical sleep-related rhythms. If confirmed by future studies, the findings could help explain why so many seemingly unrelated conditions increase the risk of cognitive decline.
Researchers also believe wearable devices that measure heart-rate variability could one day help identify people whose sleep-related brain health may be at risk.
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