Dr Michael Mosley on 4 Weeks to a Better Sleep

Article | Issue: Apr 2024

A good night’s sleep is essential for a healthy brain and body. So why do so many of us struggle to sleep well? In 4 Weeks to Better Sleep, Dr Michael Mosley explains what happens when we sleep, what triggers common sleep problems and why standard advice rarely works.

Read on for an extract …


Deep sleep and brain cleaning


When I was young, I loved reading stories from Greek mythology and one of my heroes was the super powerful Heracles (known as Hercules by the Romans). Heracles, who was the son of Zeus, was told he could be made immortal if he successfully carried out 12 apparently impossible tasks (‘the labours of Heracles’).

The least glamorous of these challenges was to clean out the Augean stables, in a single night. The Augean stables were notorious because they housed more than 3000 cattle and hadn’t been cleaned for years. You can just imagine the stink. Yet Heracles succeeded in scouring the stables of decades of accumulated dung, in the allotted time of a single night, by diverting two rivers through them.

The reason I bring up this story is that, overnight, something similar takes place inside your head. A network of channels in your brain, known as the glymphatic system, opens up and pumps cerebrospinal fluid through it while you are in deep sleep. Like the rivers in the Augean stables, this fluid flows through your brain tissue and washes away the toxic waste that has built up there during the day.

That’s the good news. The bad news is that, as we get older, we tend to get less deep sleep, which means that our brains are not as good at washing away the toxins. Young people typically get a couple of hours of deep sleep a night. When you get to my age (66), you are lucky if you are getting 30 minutes.

This matters because it is the accumulation of toxic proteins in the brain, such as beta amyloid and tau, that appears to drive Alzheimer’s disease, and in humans there is a very clear link between poor sleep and the development of dementia. Or another, more positive way of looking at this is that getting decent sleep can protect you against the risk of slowly losing your mind. There is even evidence that getting a good night’s sleep can help people who are already at high risk of developing dementia slow down progression of the disease.

In a recent study, published in May 2023, researchers from UC Berkeley’s Center for Human Sleep Science recruited 62 older adults to take part in a short trial. Before they started, the participants (who were all healthy adults without obvious signs of dementia), were asked to have a positron emission tomography (PET) scanner, to measure just how much beta-amyloid they had in their brains.

4 Weeks to a Better Sleep by Dr Michael MosleyMany of them, despite appearing healthy, already had increased levels of beta-amyloid. This group were asked to sleep in a lab while researchers monitored their sleep waves with an electroencephalography (EEG) machine.

After spending a closely monitored night’s sleep in the lab, the participants were asked to do a memory task involving matching names to faces.

It turned out that despite having high amounts of beta-amyloid deposits in their brain, the people who had managed to get lots of deep sleep performed better than expected in the memory test, and far better than the volunteers with the same amount of amyloid deposits, but who had slept worse.

The researchers say this adds to existing evidence that deep, slow-wave sleep can help protect your brain, and especially your memory, even if you already have a build-up of toxins in your brain. As one of them put it, you can think of deep sleep as being like a life raft, keeping your memory afloat, while the toxins try to drag it down into the watery depths of Alzheimer’s disease

To maximise your chance of getting more deep sleep, it is essential that you stick to a regular sleep schedule, stay mentally and physically active during the day, create a cool and dark sleep environment and minimise screen time before bed. A warm shower before turning in for the night has also been shown to increase the quality of deep, slow-wave sleep. And do try to get to bed before midnight, since your brain gets the most deep sleep during the first half of the night

Eating the right foods has also been shown to have a positive impact in boosting deep sleep.



Deep sleep and memory


As well as giving your brain a good spring clean, deep sleep is when your brain sorts out your memories and shifts the useful ones into deep storage.

During an average waking day, an awful lot happens to you. You listen to the news, read a book, go to work, talk with friends, go on social media, listen to music. In other words, you load your brain with a myriad of potential memories. Some are useful, but others can be happily discarded. It is while you are asleep (particularly in deep sleep) that your brain decides which memories it wants to keep and which to discard

It’s a bit like sorting out photos and videos on your phone. Storing images requires a lot of memory, so when your phone starts to get full, you have to edit them. Removing dud videos and photos leaves space for new ones.

Even compared to a modern computer, your brain can store an extraordinary amount of data; a recent estimate puts its storage capacity at around 1000 terabytes, which is a billion megabytes. A computer with that capacity could store around 2 billion books or 500,000 films.

Yet while you have an awesome capacity to remember things, you don’t want to store more junk up top than necessary. So, during the night, the memories that are considered important are shifted from the hippocampus (the short-term storage area of the brain) the safety of the prefrontal cortex (the long-term storage area of the brain – think of it as your hard drive). The memories left behind in short-term storage are gradually deleted.

That’s why, if you are a student, getting a good night’s sleep before an exam is so important. Staying up late and cramming is self-defeating because all those last-minute facts being madly forced in will soon be gone. You might think: ‘I’ll cut back on sleep during the week and then make up for it at the weekend.’ Unfortunately, it doesn’t work like that, because memories need to be consolidated within 24 hours of being formed.

A dramatic fall in the amount of deep sleep we typically get as we age may also explain why our ability to remember things gets worse as we get older.

In a recent study, researchers from the University of California, Berkeley,2 asked 18 healthy young adults (mostly in their twenties) and 15 healthy older adults (who were mostly in their seventies) to come into the sleep lab to take part in a memory test. Before going to bed, they were asked to memorise pairs of words, and were tested to see how well they did.

They were then attached to an EEG machine, which measured their brainwave activity while they slept. The next morning, they were tested again to see how many of the word pairs they could recall.

The researchers found that the older participants got 75% less deep sleep than the younger participants, and their ability to remember word pairs was 55% worse.

Brain scans also showed that, overnight, the youngsters were much more efficient when it came to shifting memories from the short-term storage of the hippocampus to the long-term storage of the prefrontal cortex.

One encouraging finding was that applying ‘transcranial direct current stimulation’ – a small electric buzz to the surface of the brain-enhanced deep sleep in the older participants and improved their ability to do well in the memory test. There are easier ways to enhance deep sleep than giving your brain electric shocks.


REM sleep and emotions

As we’ve seen, deep sleep is vital for cleaning out our brains and sorting our memories. REM sleep, which occurs later in the night, is also important for tidying and organising our memories; but it has the additional role of helping resolve our emotional issues.

Although we dream at other points in the night, REM sleep is when we have our most vivid dreams, and it is these dreams that help us process and deal with bad memories and experiences. All of which helps explain another very odd finding: during REM sleep most of our muscles are paralysed. This is probably so that, while in the grips of an intense, dramatic dream, we don’t thrash around and hurt ourselves. We do go on breathing, taking short, shallow breaths, but apart from that, the only part of us that is obviously moving is our eyes.

If you look at someone in REM sleep, you will see that, underneath their eyelids, their eyes are flicking madly to and fro. No one knows why this happens, but one theory is that it reflects the sort of eye movements you might make while watching a film. Dreams have been called the cinema of the mind, so perhaps the eye movements are simply a sign that you are following the action

So how does REM sleep help us process our emotions? Well, it is all to do with the amygdalae, the two almond-shaped groups of cells located deep in the brain that play a key part in regulating emotions. Let’s first look at how they work while we are awake.

I am mildly claustrophobic and, when I am in a confined space, I start to feel a sense of rising panic. That is because my amygdalae have triggered the release of ‘fight or flight’ hormones, such as adrenaline, and this in turn makes my heart rate, blood pressure and breathing shoot up. I feel nervous, sweaty and sometimes nauseous. There is a part of me that knows nothing bad is going to happen, but most of me just wants to escape from the situation.

Since the release of ‘fight or flight’ hormones plays such a big part in generating fear responses, I was fascinated to discover that REM sleep is the one time of day or night when links to these stress-inducing chemicals in the brain are switched off. This means that, while the dreams we have during REM sleep can be scary and disturbing, they are nothing like as bad as they would be if you were having them while you were awake.

Looked at this way, dreaming during REM sleep is a form of psychotherapy, where you revisit unpleasant memories and events but remain calm. This allows you to process your emotions and defuse them.


The Spider Dream

While writing this book, I asked lots of people about their sleep and their dreams. The following story, which someone told me, is a great example of a therapeutic dream: ‘When I was young I had a fear of spiders; it wasn’t terrible but I had to leave the room if I saw one. Then one night I had a dream in which I was sitting on a chair in a dark room. From the chair I could see a door. There was a light under the door and I noticed that small spiders were crawling through the gap under the door. Slowly the gap under the door got bigger and bigger and as it did larger and larger spiders started coming through. For some reason I wasn’t scared, I was just curious to see how big they would get. Then I woke up. The oddest thing is that after I had that dream, I wasn’t scared of spiders any more. In fact the next time I saw one I was able to pick it up without shrieking.’



Michael Mosley is a science presenter, journalist and executive producer. He is also the the author of the international bestselling books The Fast 800, The Clever Guts Diet, The Fast Diet, Fast Exercise and The 8-Week Blood Sugar Diet.

He recently presented Inside Porton Down: Britain’s Secret Weapons Research Facility for BBC Four and E-Cigarettes: Miracle or Menace? for BBC Two.

Visit Dr Michael Mosley’s website

Read an extract from Fast 800 Keto by Dr Michael Mosley

Author: Dr Michael Mosley

Category: Medicine

Book Format: Paperback / softback

Publisher: Simon & Schuster Australia

ISBN: 9781761425929

RRP: $34.99

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