The golden 90 minutes of deep sleep and how to get it

Deep sleep

There was a time when I would celebrate the clocks going forward combined with a bank holiday Monday lie-in. I would make sure my alarm was off the night before and sleep as much as possible the next morning expecting to feel well-rested. I wouldn’t make plans until midday the next day, and instead stay under the covers until I felt energised enough to get up.

That was before my sleep tracker taught me about deep sleep. Despite being asleep for eight hours at a time, apparently, I wasn’t getting enough of it. The statistics told me I was getting anything between 6-12 per cent or an average of one hour 17 minutes, when the ideal amounts are 20-25 per cent or 1.4-2 hours according to The Sleep Foundation.

Deep sleep is thought to be the most restorative stage for the brain, when the body removes potentially harmful materials from it. A study published in the journal JAMA Neurology in October last year found not getting enough deep sleep could have serious long-term effects on our cognitive health. The research from the Monash School of Psychological Sciences and the Turner Institute for Brain and Mental Health in Melbourne, Australia, showed that a lack of deep sleep could even increase our risk of dementia.

My biggest health fear is losing the use of my brain. So, I enlisted the help of a sleep expert to see if they could help me sort out my deep sleep issues.

Sleep stages explained

During deep sleep, growth hormones are released – promoting tissue repair and muscle growth, while the immune system renews. The brain also clears out toxins accumulated during waking hours. A lack of deep sleep has been associated with mood problems, impaired immunity and increased risk of chronic conditions (like dementia).

“If you’re lucky, you’ll next get into stage 3 deep sleep,” says Bostock. Deep sleep, also known as slow wave sleep (SWS) or stage 3 sleep is a crucial phase of the sleep cycle when the body undergoes various physiological processes which are essential for physical and mental restoration.

“The brain starts to pulse, you get a greater circulation of cerebro-spinal fluid, the body releases toxins and about 95 per cent of growth hormones are produced during this time.” Growth hormones stimulate growth and cell reproduction and is essential to mood and cognition. “There’s no doubt that deep sleep is restorative and we tend to get more of it in the first half of the night,” Bostock asserts.

In the second part of the night, you get more REM sleep which is more similar to wakefulness than other stages. “REM sleep is an active time for the brain, and great for innovation, creativity and emotional regulation,” says Bostock. Each cycle repeats every 90 minutes.

“People often assume they should go through these stages and not wake up in between,” says Bostock. “But our ancestors evolved to be able to wake up in between sleep stages, check everything is okay and go back to sleep again. If we’re in a familiar environment then we might not even notice but the older we get the more time we spend awake during sleep. So don’t get too stressed if you wake up.”

The sleep scientist weighs in

First, I needed to stop freaking out over my tracker and take more note of how I feel, Bostock advised. She would be my deep sleep coach for a few weeks during the experiment.

Research studies comparing various trackers shows they range from 50-60 per cent accurate for comparing sleep stages. They’re better than nothing but getting too obsessed about your sleep is one of the worst things to make insomnia worse, there’s even a name for it: orthosomnia.

I took Bostock’s advice and put it to the test to see if it improved my deep sleep. As well as my tracker then, I would use a simple sheet of paper to record how I felt every day.

“You have quite rigid beliefs around sleep like, ‘I need nine hours to feel great’,’’ she says. “I want you to challenge these and see if you feel alright with less sleep the next day.

“You’re getting 6-17 per cent deep sleep right now. But anything from 15-25 per cent deep sleep as an adult is actually pretty normal,” she adds. “So you’re not failing, but there are certain things you can do to try and increase that.”

My deep sleep experiment

“If light sleep wasn’t useful you wouldn’t spend half of your night in stage 2 sleep,” says Bostock. “Light sleep is still having an impact on your health. But it’s possible to do small things to impact the amount of deep sleep you get, though the changes will be subtle, small and probably slow but every bit counts,” says Bostock. “If we can try and get you a little bit more deep sleep each night, over time that will impact how you feel.”

Sleep hygiene advice tells us to sleep in a dark room, drink herbal tea before bed, have a hot bath and if we wake up in the middle of the night, get up and do something else, like the ironing, until we feel tired. I had read advice like that so many times, it seemed more tired than I was. I hate ironing. So Bostock and I decided on making five key changes that she felt would be most impactful for my deep sleep but that I felt were easy enough that I’d actually do them.

What the numbers said

The results were a surprise as I slept a little less but my deep sleep improved by 2 per cent. I also felt much better.

So during my quest for deep sleep what made a difference?

Keep a regular sleep schedule (even on bank holidays)

Your body runs on a 24-hour clock and all your organs and cells operate on this so sleep consistency is not only great for our sleep but also great for the rest of our bodies. “Massively long lie ins are tempting, but if you lie in for two hours on a Saturday and Sunday and you try to get out of bed on Monday at 6am, it’s like you have just flown in from Dubai,” says Bostock. “You’re giving yourself a type of jet lag we call social jet lag.

“If you do nothing else to improve your sleep, wake up at the same time everyday, including weekends. That allows the circadian rhythms that run within your body to be in sync and operate on the same time zone.” I was allowed to change my sleep time by 30 minutes to an hour but it’s better to stay consistent.

Don’t snooze

“Pressing snooze is counterproductive, and makes it harder to wake up,” says Bostock. It was making me more drowsy. According to a study published in the Journal of Physiological Anthropology in 2022 that found pressing snooze prolonged sleep inertia for up to 20 minutes. Sleep inertia is that groggy feeling you get when you wake up.

Anna hitting snooze
Hitting snooze can leave you feeling groggy in the morning - Heathcliff O'Malley


“The more hours you are awake and the more things you do, the more you burn this fuel called adenosine triphosphate or ATP,” says Bostock. “When you break down ATP it produces a waste substance called adenosine which makes you feel very tired – that builds sleep pressure which is essential for falling asleep naturally. So the more physical activity you do, the more you will feel the desire to sleep.”

Wake up to light

“Bright light at the start of the day is a strong cue for the body to wake up. Light lands on receptors in the back of the eye which signal a master clock in the brain which tells us to get alert and get the body moving in the morning.You could just switch on the light in the bedroom as soon as you wake up.”

Avoid caffeine after midday (or give it up)

“Cutting out caffeine or avoiding it after midday is one of the changes that makes a huge difference to people,” says Bostock. “Caffeine works by temporarily blocking sleep pressure [tiredness] by interfering with the adenosine receptors in the brain so you don’t feel sleepy.”

How do I feel afterwards?

It’s now 20 days after the experiment started. I’m still waking up at the same time each day (7am) and going to bed around the same time (11pm) give or take an hour on weekends. That was tough at first, but now I feel so much more focused and alert during the day and only really get a gnawing tiredness around 9.30pm. “That’s what we would expect,” says Bostock. “You’re building up sleep pressure so you feel tired enough in the course of a day to want to sleep at bedtime. I frankly don’t care what your tracker says, if you feel energised during the day and sleepy at night, that’s a win.”

Every little cell in my body wants to sleep in at the weekend but I make myself get out of bed by 8am (an hour later than my usual wake time of 7am). I do feel clearer during the days, with more overall energy and lost that constant morning tiredness I used to get. I keep my phone on the dressing table, about 4 metres away so when the alarm goes off, I have to get out of bed. It’s brutish but beneficial.

I stifled a well-deserved yawn when I heard the advice to cut down caffeine. But I wanted this to work so, two days before the experiment started, I gave up the two to three strong coffees and the eight cups of tea I would usually have daily. The withdrawals left a jackhammer drilling into various bits of my skull for 48 hours but after that subsided. On stressful days where my caffeine intake slipped and I had the odd afternoon coffee, I woke up restless and fitful mid-morning. I think the change to my caffeine intake was one of the most powerful.

My mood has improved immeasurably and I now (for once) believe all the things I’ve read about the mental health benefits of sleep – and the benefits of the simple changes you can make to get more of the deep variety. I’m sticking with these five changes and will hopefully continue to increase my deep sleep.

If you struggle to sleep, I recommend you try them. No camomile. No ironing.


Can't sleep? This surprising tip may help

Read more