Why Sleep Matters for Brain Health — and Alzheimer’s Disease Prevention

The Vital Functions of Sleep 

Sleep plays a fundamental role in supporting nearly every system in the body. It contributes to energy conservation, allowing the body to restore and recharge, and plays a key role in regulating the immune system, maintaining resilience against infections and inflammation. Sleep also supports physical development, tissue repair, and the balance of key metabolic and hormonal processes. It is a critical regulator of emotional wellbeing, helping us manage stress, stabilise mood, and process emotional experiences. 

Beyond these functions, sleep is also an essential pillar of cognitive health, orchestrating learning and memory consolidation—integrating new information and stabilising it into long-term memory—and contributing to overall brain maintenance. 

Although our bodies rest during sleep, the brain remains remarkably active. One of the most fascinating discoveries in neuroscience in recent years was the identification of the glymphatic system—a specialised waste clearance network unique to the brain. Similar to the lymphatic system in the rest of the body, the glymphatic system is made up of an intricate network of channels, uniquely supported by the brain’s support cells, the glial cells—hence the name “glia” + “lymphatic.” This system becomes particularly active during deep slow-wave sleep, functioning like a dishwasher for the brain, helping to rinse away waste products that accumulate during waking hours—including amyloid-beta and tau proteins, which are hallmark features of Alzheimer’s disease. When sleep is disrupted or insufficient, this vital cleaning process becomes less efficient, allowing these toxic substances to build up over time and potentially increasing the risk of neurodegeneration. 

Understanding the Architecture of Sleep 

Sleep is composed of a highly organised sequence of events/stages that repeat in cycles lasting approximately 90 minutes. These cycles alternate between two main types of sleep: Non-Rapid Eye Movement (NREM) sleep and Rapid Eye Movement (REM) sleep. 

• NREM sleep consists of three stages, progressing from light sleep (Stage N1 and N2) to deep sleep (Stage N3)—also known as slow-wave sleep. This deepest stage is important for physical restoration, immune regulation, and memory consolidation, particularly for strengthening declarative memory—that is, factual information, events, and knowledge. It is also associated with synaptic downscaling, helping the brain filter out less relevant information and reset for new learning. Additionally, research has shown that the glymphatic (brain washing system) is predominantly active during this stage. 
• During REM sleep, the brain becomes highly active—nearly as active as during wakefulness—while the body enters a state of temporary muscle paralysis, known as muscle atonia, which prevents us from physically acting out dreams. The only muscles that remain active are those involved in breathing and eye movement, resulting in the rapid eye movements that give this stage its name. REM sleep plays a critical role in emotional memory processing, creativity, procedural and motor skill learning, and brain plasticity—the brain’s unique ability to reorganise, form new connections, and integrate new experiences. 

How Sleep Changes as We Age 

Like many biological processes, sleep also changes with age—independent of health conditions or medications. 

Common age-related sleep changes include: 

• Reduced total sleep time 
• Longer time to fall asleep 
• Higer insomnia prevalence 
• Earlier sleep and wake times 
• More frequent awakenings during the night 
• Increased daytime napping 
• Decreased time spent in deep (slow-wave) sleep 

These changes can make it more difficult to feel well-rested and may also influence brain health over time. 

Sleep and Alzheimer’s Disease 

In the later stages of Alzheimer’s disease, sleep disturbances are common which is thought to result from damage to the brain systems that regulate the sleep–wake cycle. 

However, emerging research now suggests that poor sleep may not only be a consequence of Alzheimer’s disease—it may also contribute to its development. 

As we now understand that changes in the brain linked to Alzheimer’s disease can begin decades before any memory symptoms appear—a period known as the preclinical phase—studying this early stage is crucial. It can help us uncover which factors may contribute to increased risk and enable earlier identification of individuals who may be more vulnerable to disease progression. 

Emerging research suggests that people with poor or irregular sleep tend to have higher levels of beta-amyloid and tau proteins in the brain—key markers of Alzheimer’s pathology. In addition, disrupted sleep, particularly a reduction in deep (slow-wave) sleep, has been associated with reduced brain structural integrity and increased neuroinflammation, which may accelerate neurodegenerative processes over time. 

What Is the REAL AD Study Investigating? 

In the REAL AD study, we are exploring how sleep patterns relate to key Alzheimer’s disease biomarkers, brain structure and function, memory performance, and overall brain health. 

With your support and participation, we aim to answer important questions such as: 

• Can disrupted sleep indicate early biological changes in the brain? 
• Could better sleep help slow down the accumulation of Alzheimer’s-related proteins? 
• How does sleep interact with other factors like genetics, hormones, lifestyle, and brain ageing trajectories? 

What Can You Do for Your Brain Today? 

While scientists continue to investigate the precise mechanisms, there is already strong evidence that healthy sleep habits support brain health at every age. Here are some practical steps you can take: 

• Aim for seven to nine hours of sleep per night 
• Keep a regular sleep schedule, even on weekends 
• Create a dark, quiet, and cool sleep environment 
• Get exposure to natural daylight, especially in the morning 
• Reduce screen time and caffeine and alcohol intake in the evening 
• Seek medical advice if you experience snoring, insomnia, or persistent daytime tiredness 

Sleep is more than just rest—it is a powerful tool for protecting your brain. Consistently good sleep supports brain function, promotes healthy ageing, and may help lower the risk of Alzheimer’s disease—even before any symptoms appear. 

Thank you for your continued contribution to the REAL AD study—you’re helping us unlock new pathways to early detection, prevention, and healthy brain aging.