Whether it's a routine to improve sleep hygiene or a trick to fall asleep faster, most of us are pretty interested in how we can rest better without taking hours out of our day.
Of course, we all know that eight hours is the recommended amount (whether we get it or not), but as it turns out, if you're looking to learn how to sleep better, then it's more important to focus on the type of sleep you have, rather than how much of it you have.
Core sleep is the name of the game. Here, woman&home speaks to certified sleep experts, including clinical psychologists and GPs, to reveal what this type of sleep is, when we fall into it, and how to get more of it.
What is core sleep?
Core sleep, which usually takes place during the first several hours after you fall asleep, is the type of rest responsible for making your body function well. "It helps you feel your best mentally and physically," says Dr Chris Mosunic, a clinical psychologist, sleep specialist, and the chief clinical officer at Calm.
During core sleep, the body starts to restore its basic functions, which is "why sometimes even a six-hour night can feel strangely okay," he says.
"During core sleep, your emotional regulation systems cool down, giving you the capacity to deal with stress and boosting your immunity through cellular repair," he says. "It can also improve your memory through improved consolidation and processing, and help you maintain your metabolic health by balancing insulin and appetite-related hormones like leptin and ghrelin."
However, it's not a specific stage like rapid eye movement (REM) or deep sleep. According to research published in Biological Psychiatry, core sleep is "composed of stages three and four of non-REM sleep" and it's "obtained during the first three sleep cycles" of the night.
"It actually refers to multiple sleep stages of around three or four cycles, and these cycles alternate between light and deep periods of sleep," says Sandhya Bhattacharya, a psychotherapist and Counselling Directory member.
Stages of the sleep cycle
- Stage 1 (non-REM sleep): This is a stage of light sleep when you first drift off and (all being well), it only lasts for a few minutes.
- Stage 2 (non-REM sleep): Here, the heart rate slows down and the body temperature drops, getting you to the ideal temperature for sleeping.
- Stage 3 (non-REM sleep): This is often referred to as 'deep sleep' or 'slow-wave sleep'. It's essential for feeling physically restored when you wake up.
- Stage 4 (non-REM sleep): When this study was published, non-REM sleep was divided into four stages. It's now only divided into three.
- Stage 4 (REM sleep): This is the stage of sleep where dreaming happens. It plays an important role in cognitive function, memory consolidation, and emotional wellbeing.
- Throughout the night, the body cycles through these four stages every 90 minutes.
How much core sleep do you need?
The average adult needs around four to six hours of core sleep every night to hit the most vital stages of rest and protect their baseline functioning, says Dr Mosunic. "While eight hours of sleep is the common recommendation, what really matters is the quality and composition of those core sleep hours," he notes.
If you're overtired or go to bed late, your body will often prioritise deep and REM sleep to compensate. But if your core sleep is constantly disrupted and you're often in this overtired state, you'll find it harder to recover from daily activities and focus during the day.
"The minimum gives you a survival baseline, it's not a long-term strategy for thriving," says the doctor.
How to get more core sleep
- Create consistency: "Going to bed and waking up around the same time each day helps your brain anticipate when to start producing melatonin, so aim for a general bedtime window," says Dr Mosunic.
- Protect the first four to six hours: This is all about sleep hygiene. "To help minimise anything that could interrupt the start of your sleep, silence your phone, turn on white noise, and use blackout curtains. You could also let anyone living with you know if you’re going to bed early so they know to keep it down," he says.
- Cut back on caffeine: "Caffeine has a half-life of about five to six hours, which means your afternoon coffee could still be buzzing through your system at bedtime," he says. To avoid the impact, switch to caffeine alternatives like peppermint tea.
- Practice mindfulness: "Practice psychological relaxation techniques prior to sleep," suggests Dr Hana Patel, an NHS GP and resident sleep expert at Time4Sleep. This could include some light movement as well - Tai Chi for sleep, for example.
Is light sleep important?
Core sleep is obviously very important, and the focus is often on prioritising REM and deep sleep, but light sleep is still essential. "It's crucial to the sleep cycle, both in moving towards core sleep and emerging from it," says Bhattacharya.
Without light sleep, you can't move into deep or REM sleep, and if you like to nap to restore your energy levels, then it's even more important, notes Dr Patel.
"When we nap, our bodies still undergo the same stages of sleep at night that make up a sleep cycle. However, there is much less time to cycle through these stages. A short nap, where you may only spend a little time, if any, in deeper sleep and REM sleep, can make you feel refreshed when you wake up," she says.
