Dementia Life Review: Why We Sleep by Matthew Walker

Review

Dementia Life Review: Why We Sleep by Matthew Walker — Sleep, Night Shifts, and Dementia Risk

I want to talk about sleep. It’s a topic that I’ve certainly had a love-hate relationship with over the years. I’ve been reading Why We Sleep, the number one Sunday Times Bestseller, by Professor Matthew Walker. Walker is a British neuroscientist and Professor of Neuroscience and Psychology at the University of California, Berkeley, where he directs the Center for Human Sleep Science. He’s also a former professor of psychiatry at Harvard. He’s spent over 20 years studying the science of sleep and its impact on human health.

This is a little out of the ordinary for the Dementia Life blog but I thought it would make for interesting reading. I’m not going to summarise the book, but there are a few elements that I want to pull out and expand on for discussion within this article. Even since reading Why We Sleep it’s changed my perception of how important sleep is, and it made me think about my mum.

How Sleep Affects Our Health

Matthew Walker suggests that a lack of sleep, in both duration and sleep quality, can be an important factor for people’s overall health. I think that all of us can testify to the fact that an extended period of time with poor sleep or a lack of sleep in general can make us feel ill. And I know that if I suffer from a bout of poor sleep, I can normally count down until I get some sort of cold or bug.

I’m not going to try and pretend to be a scientist, a sleep researcher or a professor trained in any of this, but I’m going to explain this as I understood it. As humans, our circadian rhythm means that we are hardwired to get somewhere between 7 and 9 hours of sleep per night. The shift in chemicals our bodies release throughout the day — especially the rise and fall of adenosine and melatonin — show that we are designed to feel sleepy towards the end of the day, sleep overnight to refresh our brains, and then give us the best start to the following day.

Adenosine is a chemical that builds up in your brain throughout the day, creating what’s known as “sleep pressure.” The longer you’re awake, the more adenosine accumulates, and the sleepier you feel. When you finally get a good night’s sleep, your brain clears it away, and you wake up feeling refreshed. Melatonin works alongside it but does something different — it signals darkness and timing, essentially telling your body when it’s time to wind down. The two work together, but they’re not the same thing.

Night Shift Work and Dementia Risk: Why This Hit Home

As many of you will be aware, my mum used to be a carer for people with dementia. She worked in multiple care homes throughout my life. When I was a young child, I think up until I was about 5 or 6, my mum worked nights. I take my hat off to people that work nights. I’m not a particularly good sleeper but the thought of switching what hours of the day I’m actively doing anything isn’t appealing.

So, if our sleep is primarily linked to the release of these chemicals and the release of these chemicals is set to happen at regular intervals throughout the day, then what happens if you work nights for an extended period of time?

Luckily for me — there has been some extensive research into the topic.

There have been several large-scale studies looking at the link between night shift work and dementia risk. One study that followed over 245,000 people in the UK for more than a decade found that people who always worked night shifts had a significantly higher risk of developing dementia compared to those who worked regular daytime hours. Permanent night shift workers had roughly a 47% higher risk, and even irregular shift workers showed about a 20% increase. A separate review that combined the findings of multiple studies found a consistent, modest increase in dementia risk among long-term night workers — around 12–13% higher than those who never worked nights.

Another dose-response meta-analysis found that the risk of dementia increased by approximately 1% with each additional year of shift work. Interestingly, the curve was steepest in the first seven years, suggesting that even relatively short periods of night work may have an impact.

What Happens in Your Brain While You Sleep: The Glymphatic System

Part of the reason for this link between poor sleep and dementia risk may come down to what’s happening in the brain while we sleep. Research has shown that our brains have their own waste clearance system — sometimes called the glymphatic system — that kicks into gear during deep sleep.

Think of it like this: during the day, your brain produces waste as a by-product of all that thinking, processing and functioning. One of the key waste products is a protein called beta-amyloid, which is one of the proteins linked to Alzheimer’s disease. When you sleep, especially during the deepest stages of sleep, the spaces between your brain cells actually expand, allowing cerebrospinal fluid to flow through and flush these waste products out. It’s essentially a deep clean for your brain.

Studies have shown that even one night of poor sleep can lead to increased levels of beta-amyloid in the brain. A study published in the Proceedings of the National Academy of Sciences used brain imaging to demonstrate that a single night of sleep deprivation resulted in a measurable increase in beta-amyloid build-up, particularly in brain regions associated with Alzheimer’s disease.

More recently, a 2026 study published in Nature Communications provided some of the strongest evidence yet that this glymphatic clearance system works actively during sleep in humans — not just in mice, which is where much of the earlier research had been done. The study found that normal sleep significantly enhanced the overnight clearance of Alzheimer’s-related proteins into the bloodstream, compared with sleep deprivation.

Over years, the thinking goes, chronically disrupted sleep could allow these waste products to build up. The science is still evolving, and researchers are careful to point out that shift work alone doesn’t cause dementia — there are lots of other factors at play, including genetics, lifestyle, and overall health. But the evidence is building that long-term disruption to our sleep patterns is something worth paying attention to.

A Balanced View: Criticisms of Why We Sleep

I want to make sure that everyone reading this gets a completely balanced view. I enjoyed the book and think it would be a worthwhile read for the Dementia Life community, but it would be wrong of me not to tell you that the book is not without criticism. I want to make sure that you get as close to the whole picture as possible, and even I will have missed some things or interpreted something differently to you. We all know that every dementia journey is different, and the information and guidance that helps people will be different depending on the person. Please bear this in mind when taking the decision to read the book or taking any action based on what you’ve read here.

So, in the interests of balance, here’s what you should know.

Statistical errors and overstated claims

In 2019, an independent researcher named Alexey Guzey published a detailed, chapter-by-chapter critique of the book. Guzey argued that Walker had made a number of factual and statistical errors, even within the first chapter alone. He claims to have spent over 130 hours fact-checking that single chapter and found what he considered to be significant inaccuracies in how the data was presented.

One of the more serious allegations was that Walker appeared to have omitted a bar from a graph when reproducing research data, which made the findings look more clear-cut than the original source suggested. Andrew Gelman, a well-known statistician at Columbia University, discussed Guzey’s critique and suggested that the omission of data from the graph entered what he described as “research misconduct” territory. UC Berkeley conducted an inquiry and concluded the errors were minor and unintentional. Walker published corrections and acknowledged the need to revise the book.

Alarmism and sleep anxiety

Perhaps the criticism most relevant to our community is that the book’s tone may cause unnecessary anxiety around sleep. Some sleep professionals reported that patients who had previously slept well developed insomnia and sleep-related anxiety after reading the book. Sleep coaches described seeing people who naturally slept well on less than eight hours become fearful that they were damaging their health, tried to force more sleep, and ended up sleeping worse as a result.

This is important for anyone caring for a loved one with dementia. If you’re a carer reading this and you’re already struggling to sleep, the last thing I want is for this blog — or the book — to make that worse. The goal here isn’t to frighten you. It’s to gently encourage you to prioritise rest where you can.

The eight-hour debate

Walker strongly advocates for eight hours of sleep per night. However, other researchers in the field have pushed back on this as a one-size-fits-all recommendation. Sleep researcher Jim Horne, among others, has argued that not everyone needs eight hours and that individual sleep needs vary. The NHS and most health bodies recommend 7–9 hours for adults, acknowledging that the right amount depends on the person. Bill Gates, while broadly endorsing the book, also noted he wasn’t fully convinced by Walker’s claims about the strength of the link between sleep and Alzheimer’s disease.

Walker’s response

To his credit, Walker has acknowledged errors and published corrections. He posted detailed responses on his blog addressing many of the specific criticisms, and a revised edition of the book has been produced. He has also described the process of correcting errors as part of good scholarly conduct. The criticism was discussed on the BBC’s More or Less programme, which gave both sides a fair hearing.

None of this means the book isn’t worth reading. The core message — that sleep matters for our health, including our brain health — is well supported by a broad body of research that goes far beyond Walker’s book. But it’s worth going in with your eyes open and treating it as one perspective, not the definitive word.

What This Means If You’re Caring for Someone With Dementia

I really don’t want this to be alarmist. I don’t want you reading this to suddenly decide to quit your job or worry that if you have a night of bad sleep you’re going to get Alzheimer’s. The reason for writing this is much simpler than that: it’s a reminder to look after yourself and put a focus on your self-care, especially if you’re looking after a loved one with dementia.

Looking after a loved one can be terrifying, stressful and all-consuming. This can wreak havoc with our sleep patterns — the ever-churning mind, wondering if you’re going to get a call saying they’ve wandered off through the night. We get lots of stories from people in our group about getting calls at 2am, or their spouse going through some intense sundowning. I just want this blog to be a gentle reminder to do something that is just for you when you can. An afternoon walk, a cup of chamomile tea in the evenings, or even just picking up a book for an hour before bed.

Look After Yourselves

I think about my mum working those night shifts, doing it for years so she could look after us during the day. I think about all of the night shift workers in care homes right now, looking after people with dementia while potentially putting their own health at risk. And I think about the carers reading this who haven’t slept properly in months because they’re listening out for a door opening or a phone ringing.

None of us can go back and change the sleep we’ve lost. But we can start paying attention to it now. Not with guilt — there’s enough of that going around already. Just with a quiet acknowledgement that sleep isn’t a luxury. It’s not laziness. It’s one of the most important things your body and brain need to function.

So tonight, if you can, put the phone down a bit earlier. Let someone else take the late shift if that’s possible. And if it’s not — if tonight is another broken one — then be kind to yourself about it. You’re doing something incredibly hard, and the fact that you’re still showing up is enough.

Look after yourselves. You matter too.

A Note From Jack

I want to make sure that everyone reading this gets a completely balanced view. I enjoyed Why We Sleep and think it is a worthwhile read for the Dementia Life community, but the book is not without criticism and I think it’s important you know that.

I’ve done my best to present the research and the criticisms fairly, but I am not a scientist, a doctor, or a sleep researcher. I will have missed things, and I may have interpreted something differently to how you would. We all know that every dementia journey is different, and the information and guidance that helps one person will be different for another.

Please bear this in mind when deciding whether to read the book or when considering any changes to your own routine. If you have concerns about your sleep or your health, please speak to your GP.

This article is written from my perspective as a carer and the founder of Dementia Life. It is not medical advice.