The Link Between Sleep Stages & Alzheimer’s

Written by Hilary Ma, Edited by Amy Chan

As children, we were always taught the importance of sleep; doctors warning of the consequences, parents enforcing the dreaded bedtimes that seemed way too early. In today's society, though, sleep deprivation has become increasingly common and normalized amongst teenagers and adults alike. Overworked people casually joke about how little sleep they get, but the reality is that the harmful consequences are often overlooked. Sleep deprivation alters your entire brain chemistry, fogging your brain and making it difficult to focus or control your behaviors, as well as being linked to physical and mental health issues. Specifically, a recent study has confirmed that a deficit in certain sleep stages contributes to the degenerative brain disease that affects approximately 6.7 million Americans over the age of 65, namely Alzheimer’s disease. 

The Science of Sleep Stages

To understand this link, we must first be familiar with the different stages of sleep that cycle throughout the night:

• NREM Stage 1 (N1): Stage 1 is when a person first falls asleep and lasts about 1-7 minutes each cycle. Although the body is not fully relaxed, the brain and body begin to slow. If interrupted, a person is not likely to cycle through this stage again for the night (Suni, 2023).

• NREM Stage 2 (N2): Stage 2 lasts for 10-25 minutes. A person spends approximately half their sleep in this stage with the possibility of each time cycling through getting longer. The body drops in temperature, muscles relax, and breathing and heart rate slow (Suni, 2023).

• NREM Stage 3 (N3): Stage 3 is critical for restorative sleep, which allows the body to recover and grow. This stage lasts for 20-40 minutes during earlier cycles but gets shorter as you sleep (Suni, 2023).

• REM Stage 4 (REM Sleep): During this stage, brain activity actually picks up, but the body’s muscles experience a paralysis besides the eye and muscles that control breathing. This stage is essential for memory, learning creativity, etc, and is associated with vivid dreams. Unlike Stage 3, REM stages typically get longer as you sleep, making up around 25% of sleep (Suni, 2023).

The Study

Alzheimer's disease has impacted millions worldwide, with no definitive cure once diagnosed, and the number of cases is only projected to double by 2060. However, a study published in the Journal of Clinical Sleep Medicine from the American Academy of Sleep Medicine found potential opportunities to decrease the risks of developing it in the first place. These researchers conducted a study consisting of 270 participants with a median age of 61 years, 53% female, and all white. Additionally, individuals were excluded from this study if they previously had substantial damage or disease to the brain, such as a stroke or probable dementia (Theffron, 2025). Polysomnography, a diagnostic test that monitors sleep stages and cycles, was used, followed by an MRI to examine the anatomical features of the brain after the 13 to 17 years. The results showed that a reduction of Stage 3 and REM sleep was associated with brain atrophy in the inferior parietal region, a change that can be associated with Alzheimer's disease. It’s well known that sleep is crucial for many functions such as learning, memory, cognition, repair, maintenance, and many more–most of which occur in Stage 3 and REM sleep. Among these functions is the clearance of brain waste, which is especially important in the prevention of Alzheimer's, as it is characterized by a buildup of junk proteins in the brain (Newman, 2025). These findings are certainly intriguing and further reinforce the well-established importance of sleep for the body’s functions.

What Can We Do Now?

While researchers are calling for further research with more diverse participant groups, one fact remains clear: sleep is crucial. What you can do now is to prioritize your well-being by improving your sleep. This can be easier said than done, though, so here are some tips that could help:

• Cutting caffeine 10 hours before bed: Caffeine tends to stay in your body longer than most people realize, keeping you up when you don’t want to (Newman, 2025).

• Avoid large meals or alcohol before bedtime: It’s recommended to finish your last meal and to cut alcohol 3 hours before bedtime (Newman, 2025).

• Keep a consistent schedule: Go to bed and wake up at the same time everyday (CDC, 2024).

• Limit screen time: Turn off your electronics 30 minutes to 1 hour before bedtime (CDC, 2024).

• Maintaining a sleep-friendly environment: Keep your room cool, quiet, and relaxing (CDC, 2024).

• Keep a sleep diary: If you struggle with sleep, it may be a good idea to track your habits to see what’s going on. This can include tracking sleep times, naps, drink and alcohol intake, medications, etc (CDC, 2024).

References

CDC. “About Sleep.” Cdc.gov, 15 May 2024, www.cdc.gov/sleep/about/index.html.

Newman, Tim. “Spending Less Time in 2 Deep Sleep Stages May Contribute to Alzheimer’s.” Medicalnewstoday.com, Medical News Today, 3 Apr. 2025, www.medicalnewstoday.com/articles/lower-proportions-time-2-sleep-stages-may-contribute-alzheimers#Limitations-and-more-questions-to-answer. Accessed 12 Apr. 2025.

Suni, Eric, and Abhinav Singh. “Stages of Sleep: What Happens in a Sleep Cycle.” Sleep Foundation, Sleep Foundation, 8 Dec. 2023, www.sleepfoundation.org/stages-of-sleep.

theffron. “Study Links Sleep to Brain Changes Seen in Alzheimer’s Disease.” American Academy of Sleep Medicine – Association for Sleep Clinicians and Researchers, 31 Mar. 2025, aasm.org/study-sleep-stages-brain-changes-alzheimers-disease/. Accessed 12 Apr. 2025.