A new study suggests that deep sleep—also known as non-REM slow-wave sleep—may help protect cognitive abilities even in people showing early signs of Alzheimer's disease. Researchers from the universities of California (Berkeley), Stanford, and UC Irvine studied 62 healthy older adults and found that those with Alzheimer's brain markers who experienced good quality deep sleep performed better on memory tests. The study highlights that deep sleep might act as a protective factor against cognitive decline, even when characteristic brain changes are present. Alzheimer's disease is often marked by the accumulation of beta-amyloid proteins in the brain, which can start forming decades before symptoms appear. Earlier research has linked poor sleep with higher levels of these proteins. Deep sleep seems to play a key role in clearing metabolic waste, including these harmful proteins, from the brain. This "brain cleaning" process may explain why good quality sleep can protect cognitive function, even when Alzheimer's-related biological markers are present. Another study following 700 women over five years suggests that increased daytime fatigue and the urge to sleep may be early signs of dementia. However, the protective effect of sleep is specifically tied to deep sleep, not other sleep stages. Neuroscientist Matthew Walker from the University of California at Berkeley described deep sleep as a "life jacket that keeps memory afloat, preventing it from being dragged to the bottom by the weight of Alzheimer's-related pathologies." Zsófia Zavecz, a neuroscientist at UC Berkeley and lead author of the study, noted that the presence of brain pathologies does not automatically lead to cognitive symptoms or memory problems. The study, published in the journal BMC Medicine, suggests that certain lifestyle factors, particularly deep sleep, can reduce the impact of these biological changes. Experts recommend several practices to improve deep sleep, such as avoiding caffeine in the late afternoon, engaging in regular physical activity, limiting screen time before bed, and taking a warm shower before going to sleep. These habits can enhance the duration and quality of deep sleep, thereby strengthening the brain's resilience against Alzheimer's-related changes. While the study's sample size is relatively small, the findings offer promising insights into simple, accessible ways to prevent cognitive decline. Researchers stress the need for longer-term studies to confirm if improving deep sleep can indeed preserve cognitive functions over time, even as beta-amyloid levels rise. Sleep quality may become a key element in dementia prevention, along with other factors like education, physical activity, and social engagement.