It’s deep sleep you really need – and here’s how to get much more

DURING my countless wretched hours spent trying, and failing, to fall asleep, I’ve often wondered: Why do we need to sleep at all? Well, after years of intense research into the weird and wonderful world of the sleeping brain, I have a pretty good idea.

And it is quite astounding. Just about everything you rely on your brain to do while you are awake is only possible due to complex processes that happen while you’re asleep.

According to anthropologists, the evolution of our subconscious brain workings is part of the reason human beings have risen to the top of the animal kingdom.

It turns out the best stuff happens during what scientists call deep sleep, which occurs about an hour into falling asleep. So rather than fretting about the number of hours you get, it’s far better to improve the quality of the sleep you do have.

And, contrary to popular thought, the way to do this is not by drinking mugs of hot milk or listening to whale music.

You’ll find more of the remedies that don’t work in the panel on the next page – and some that do later on.

But first, I want you to join me on a magical, mysterious tour inside our sleeping brains.

Have you ever wondered why, just before falling asleep, you feel as though you’re falling off a cliff or a bridge and suddenly kick out your leg? Or if there’s any physiological point in dreaming?

Here, I’ll explain everything you’ve ever wanted to know about what happens when we sleep – and why each stage is so important.

Let’ s start with the three distinct states: light sleep, deep sleep and rapid eye movement (REM) sleep.

We sleep in roughly 90-minute cycles through the night, flipping between one state and another. After about an hour of light sleep, you’ll slip into deep sleep, when you are hardest to rouse. Involuntary twitches are common between these two states, as the brain transitions from one to the other.

Deep sleep occurs during the first half of the night, and the second half of the night is dominated by REM sleep.

We’ll get to REM sleep – which is where dreams usually occur – a bit later. But deep sleep, which totals a couple of hours each night in young, healthy people, is where most of the brilliant stuff happens. Millions of neurons in the brain are firing all at once, pausing, then firing again. This process ensures that lots of important repair work, all over t he body, gets done. Your pituitary gland – a gland below the base of the brain – starts to secrete more growth hormones, which are vital for cell growth and healing. Deep sleep also helps you fight infections by creating more cytokines, a type of protein that regulates your immune system. Another essential role of deep sleep is washing away toxins that have built up in your brain throughout the day. Your brain does this via a network of channels, known as the glymphatic system. These channels open up and pump cerebrospinal fluid through your brain tissue while you are in deep sleep. As we get older, sleep becomes more fragmented – although it’s not totally clear why older people sleep less well. It means our brain, and the glymphatic system, becomes less able to complete this ‘washing’ process.

Scientists have suggested that this may be one of the reasons the risk of Alzheimer’s increases as we age, because broken sleep means there is less opportunity to wash away toxic proteins in the brain that are responsible for the disease.

STORAGE SYSTEM SORTS OUT OUR MEMORIES

HAVE you ever wondered why, out of the hundreds of sights, sounds and tastes that happen to you everyday, you only remember a select few?

The answer lies with your sleeping brain – which is rather like a sophisticated sorting office. An hour or so into deep sleep, your brain begins deciding which memories it wants to keep and which to discard, leaving space for new ones.

Memories considered important are shifted from the hippocampus (the short-term storage area) to the safety of the prefrontal cortex, for long- term storage. The memories left

behind in the hippocampus are deleted. It’s like sorting out photos and videos on your phone and getting rid of the duds to free up space. One recent estimate puts the brain’s storage capacity at 1,000 terabytes, which is a billion megabytes.

A computer with that capacity could store around two billion books. Scientists believe this holds some of the answers as to why we become more forgetful as we age. Studies show that the less deep sleep we get – remember, the older we get, the less we sleep – the more forgetful we are.

Researchers at the University of Berkeley measured the sleeping brain activity of twenty-somethings and over 70s. They found that the older volunteers got 75 per cent less deep sleep than their younger counterparts. When they were tested on memory tasks, the over 70s performed much more poorly than the twenty-somethings. In fact, as soon as we hit 50, the amount of deep sleep we get dramatically reduces. And by the time you get to my age – 63 – you’re averaging 30 minutes nightly.

HOW DREAMING HELPS US ALL COPE WITH TRAUMA

THE second half of the night is when we enter the state everyone wants to know about – dreaming. Or, more specifically, the peculiar state of repetitive eye movement, or REM. If we’re going to dream, this is when we’re most likely to do so. If you ever get the chance to, watch somebody while they’re in the second half of sleep – it’s rather extraordinary. You’ll notice their breathing becoming short and shallow. They may seem more bonded to the bed, as the muscles become paralysed. Underneath the eyelids their eyes begin flicking madly to and fro.

Sleep scientists think this is probably a sign that we’re in the middle of a vivid dream. It’s thought that these strange eye movements allow us to change from one scene to another, a bit like watching a film.

But dreams aren’t just for our entertainment – they play a crucial role in helping us to work through painful memories. This is also why most of our muscles are paralysed during REM sleep. If you are in the grips of an i ntense, dramatic dream, we don’t want to be thrashing around and hurting ourselves.

So how does REM sleep help us process our emotions? It is all to do with our brains’ emotion centre, the amygdala – the two almondshaped groups of cells located deep in the brain. When we are awake and encounter stressful situations, the amygdala triggers the release of ‘fight or flight’ hormones such as adrenaline. This causes your heart rate and blood pressure to shoot up, breathing gets rapid and you feel nervous, sweaty and sometimes nauseous. But during REM sleep, the amygdala switches off this reaction. 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 awake. It means you can revisit unpleasant memories, but remain calm, which allows you to process your emotions and defuse them. And different dreams give us clues to our underlying emotions. Our brains then try to work through it at a time with physical symptoms paused.

Anxiety is a particularly common feeling to crop up in dreams. If you’ve ever dreamt your teeth are falling out, you’re falling off a cliff or high building, or speaking in a public space without clothes on, you’re probably feeling anxious.

My most common anxiety dream is driving too fast along a narrow road and then plunging down a cliff to my death. My wife tells me I sometimes drive too fast – perhaps my dreams are telling me I should listen to her. If you are plagued by dreams such as these, it suggests there is a lot of stress in your life that you might want to address.

But dreams can have a positive effect, too. Research has shown that a sleep rich in REM increases our ability to come up with novel ideas and solutions to problems.

There are lots of lovely stories about people who have had their eureka moments while they slept.

Paul McCartney says the tune for Yesterday came to him while he was asleep, and the Rolling Stones’ Keith Richards came up with the opening verse to Satisfaction.

WHY ROUTINE, EXERCISE (AND SEX) ARE CRUCIAL

SO HOW can you improve the amount of deep sleep, to reap all its benefits? First, work out how much of this high-quality sleep you are getting, by calculating your sleep efficiency. Use a wearable sleeptracker, such as a Fitbit, to precisely record the amount of time you spend asleep, and keep track of how many hours you spend in bed. Then, convert hours into minutes. If total time in bed is eight hours and 30 minutes, that’s 510 minutes

If total time asleep is six hours and 10 minutes, that’s 370 minutes.

Then, divide the first by the second. In this case, your sleep efficiency is 370/510 = 72.5 per cent.

A score above 85 per cent is good, but less than 80 per cent suggests you are struggling. If you are in bed for eight hours each night, but only sleep for six, then your sleep efficiency is 6/8, or 75 per cent, which is poor.

Thankfully, there are sciencebacked ways to improve this.

If your lack of deep sleep is having a significant effect on your mood, memory and ability to concentrate, you may want to try sleeprestriction t herapy – which I explained earlier.

Otherwise, the key to improving your sleep efficiency is to establish a good routine. That starts with getting up at the same time every day. You should aim to get at least 30 minutes of morning light as soon as you can – this will help reset your circadian clock, the time keeper in your brain that tells you when to sleep and when to wake up.

Also, exercise, at any time of day, will help you sleep. Studies show that resistance exercise such as press-ups and squats are particularly effective for improving deep sleep. I try to do 40 of each when I get out of bed in the morning.

There’s something else that might help, too – sex. Australian studies have found that intimate moments result in significant reductions in stress hormones such as cortisol, which can inhibit deep sleep.

Fast Asleep: How To Get A Really Good Night’s Rest, by Dr Michael Mosley, published by Short Books, is out now.