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Listen to Story Sleep is essential for the brain, and a new study has found that not getting enough of it can do more harm than we realise. Scientists now say that poor sleep quality could shrink parts of the brain and increase the risk of Alzheimer's disease . Alzheimer's disease is the most common type of dementia, in which a person gradually loses memory, cognitive thinking, the ability to reason and to do simple daily tasks.
In Alzheimer's, the brain starts shrinking progressively. It is the most common neurodegenerative disease in the world. The research caught the attention of tech billionaire Elon Musk, who is known for working long hours with little sleep.
He reacted with an "Uh oh" after reading about the findings. Uh oh https://t.co/honuEbFoOw — Elon Musk (@elonmusk) April 2, 2025 In the past, Musk admitted to sleeping less than six hours a night and going to bed at 3 am.
The study, published in the Journal of Clinical Sleep Medicine , tracked over 270 adults for more than a decade. It found that people who got less deep sleep (called slow-wave sleep) and REM sleep (the stage linked with dreaming) had smaller brain regions that are typically affected early in Alzheimer’s. These regions, like the inferior parietal cortex, are important for memory and thinking.
Scientists used brain scans and sleep studies to make these connections. Alzheimer's disease is the most common type of dementia. (Photo: Getty Images) "Reduced brain activity during sleep may contribute to brain shrinkage," said researcher Gawon Cho, Yale School of Medicine.
Even after considering other health factors, poor sleep remained a strong risk factor. So, what exactly is slow-wave and REM sleep? Our brain cycles through four stages of sleep every night, from light sleep to deep sleep (slow-wave), and then REM sleep. According to Medical News Today, these are the four phases of sleep: Stage 1: The first stage once you have dropped off.
It is relatively light sleep. Muscles begin to relax. It lasts for just 1 to 5 minutes.
Stage 2: Slightly deeper, this phase lasts around 25 minutes. The body relaxes further. Stage 3: This is the deepest stage of sleep.
Heart rate, breathing, and brain waves become more regular. Stage 3 is also called slow-wave sleep. Stage 4: This stage is also called rapid-eye movement (REM) sleep due to the movement of the eyes in this phase.
During REM sleep, breathing becomes faster and blood pressure and heart rate become less regular. The first stage of sleep is relatively light sleep. Muscles begin to relax.
It lasts for just 1–5 minutes. (Photo: Getty Images) People generally cycle through these four phases 4 to 6 times each night. Both deep and REM sleep are essential for brain health.
The researchers believe that deep sleep helps clear toxins from the brain . Less of it may cause harmful build-up and brain atrophy or shrinkage. With few treatments available for Alzheimer’s, scientists say improving sleep could be a powerful way to protect the brain.
And perhaps, even convince the busiest minds, like Musk, to hit snooze a little earlier..
