We spend between a third and a quarter of our lives asleep, so it’s important to our lives. Originally thought to be a passive activity, studies now show that when we’re asleep, our brain is engaged in a number of activities that have important implications for our health and well-being. This means sleep isn’t simply the absence of wakefulness, but an active and metabolically different state. As such, it needs to carry equal standing alongside balanced nutrition and adequate exercise as essential components for achieving and maintaining good health.
What is sleep?
There are two main types of sleep that our brains cycle through: REM (rapid eye movement) and non-REM sleep. First, we’ll enter non-REM sleep, which typically involves four stages: the first occurs just as we doze off, the second is light sleep (when our body temperature drops and our breathing and heart rate regulate) and the third and fourth involve deep sleep. The majority of stages three and four takes place during the first third of the night, making the time you go to bed an important determinant of getting a good night’s slumber.
Although we originally believed REM sleep, which occurs after stage four, to be the most important, research now suggests that the early stages of sleep are just as essential for learning, memory, restoration and repair. As we cycle into REM sleep, our eyes start to move rapidly behind our eyelids, and brain waves are similar to those when we are awake. Our breath rate increases and our body will become temporarily paralysed as we dream – if you wake during REM sleep, you’re 80% more likely to vividly recollect your dreams.
Sleep cycles repeat about four or five times during the night, but with progressively less time spent in the initial sleep stages and more time spent in REM sleep.
Why is sleep important?
If you’ve ever risen after a poor night’s sleep, you’ll be well aware of how it makes you feel: tired, irritable and with a less-than-clear-thinking brain. Getting a good night’s sleep is important to energise us through the following day, but also for our brain to work well.
A good night’s sleep improves our brain’s ability to adapt to inputs – it helps us learn better, process memories more accurately, develop young brains and clear our brain’s waste products more efficiently.
That said, a good night’s sleep doesn’t just impact how we learn and remember, it also has important consequences for our immune function, metabolism and hormonal balance. Poor sleep can make us more prone to infection and illness, disrupt our blood sugar balance and lead to high blood pressure, increase depressive states and make headaches and migraines worse.
The stages of deep sleep are especially important, because they enable the brain to process and file memories, deal with anxiety and initiate repair and restoration.
How much sleep do I need?
How much sleep each of us needs depends on our own unique characteristics – gender, genetic make-up, life stage – as well as environmental and behavioural factors. The following are guidelines and relevant for healthy individuals who do not suffer from a sleep disorder.
Children (three to five years): 10-13 hours regularly per night
Children (six to 13 years): 9-12 hours regularly per night
Helping your child reach their guideline number of hours on a regular basis is associated with better outcomes, including improved attention, behaviour, learning, memory and emotional regulation. This may be partly explained by the fact that younger children spend a greater length of time in the deep sleep stages three and four.
Adolescents (14-17 years): 8-10 hours regularly per night
This group is one that is at risk of sleep deficits, that’s because they are more likely to be exposed to artificial light in the hours preceding bed; this, combined with the hormonal shifts of puberty, may predispose them towards an evening chronotype, making them less likely to benefit from morning daylight and the positive influences that has on circadian rhythms. Add to this the demands of a school timetable, and it’s easy to see how sleep deficits can arise. Sticking rigidly to a fixed bedtime, although unpopular, will support REM sleep.
Young adults (18-25 years): 7-9 hours regularly per night
Younger adults, similar to adolescents, may require more sleep, especially if they are recovering from sleep debt. They too may be influenced by late-night use of electronics, lack of physical activity and over-consumption of caffeine.
Adults (25-65 years): 7-8.5 hours regularly per night
Adults have the additional demands of work worries, social commitments and family dynamics to contend with – all of these may influence their ability to fall asleep and stay asleep. During our younger adulthood, fragmented sleep often involves waking from REM sleep; this tendency protects the important deep sleep stages. However, this protective mechanism declines with age, resulting in disturbances to non-REM sleep, too.
Older adults (from 65 years): 7-8.5 hours, regularly per night
As age increases, we find it harder to fall asleep and stay asleep. At this life stage, we may also experience a circadian shift towards a morning chronotype, which means earlier bed and rise times. For the elderly, sleep duration may appear good, but it tends to be sleep quality that is affected by frequent waking.
Is quality sleep more important than quantity?
Although we tend to focus on the amount of time we perceive we’ve been asleep, there are other relevant factors that determine how beneficial our sleep may be. By asking yourself the following questions you may help clarify just how restful your sleep is:
- Efficiency – how much of the time in bed do you actually spend asleep?
- Timing – are your bedtime and wake times appropriate to allow you to reach your recommended sleep time?
- Consistency – is there any variability to your sleep from night to night?
- Satisfaction – how rested and restored do you feel next morning?
In addition to this, your sleep quality will be dependent on adequately completing the required cycles and stages of sleep; this requires your brain to consolidate and organise the cycles satisfactorily across the night.
What are the downsides of getting too little or too much sleep?
Sleeping less than 7 hours regularly per night is associated with weight gain, obesity, diabetes, heart disease, stroke and depression. It’s also likely to increase our chances of illness, put us at greater risk of accidents, heighten the sensation of pain and result in poor physical and mental performance.
This applies to children and young adults too; they are likely to experience decreased glucose tolerance and insulin sensitivity, increased evening cortisol and disruptions to the hormones (ghrelin and leptin) that control appetite.
Growth hormone is released around the clock, but it is at night that it peaks, typically during the first 90 minutes of sleep. If we stay up late and delay sleep, we don’t experience the growth hormone peak that night – if we do this on a consistent basis, it may affect growth and development and result in decreased muscle mass and exercise capacity.
Is a sleep tracker helpful?
Fitness trackers and smartphone apps are becoming increasingly popular – they assess sleep duration and, in some cases, sleep quality. The algorithms used on these devices are proprietary, and evidence suggests they may underestimate sleep disruptions and overestimate sleep duration and quality. That said, many users find them helpful because they highlight the importance of sleep and provide some form of indicative measure.
Tips for a quality night of sleep
Creating the right environment and easing yourself towards restful sleep during those important minutes before you head to bed can make all the difference. Here are some tips to help promote a restful night:
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- Try some sleep supportive foods
- Have a warm bath leading up to (but not immediately before) bedtime – sleep is accompanied by a decrease in core body temperature, and warming up in the hours before bed appears to help promote sleep and improve its depth
- Make your bedroom a quiet and relaxing space, and keep the room temperature at a comfortable 16-19C
- Set a bedtime that is early enough for you to enjoy your recommended hours of sleep
- What you wear in bed influences both how quickly you fall asleep and how deep the sleep you enjoy – at cooler temperatures (17C), wool nightwear works best, while at hotter room temperatures (22C), consider cotton
For more tips, check out our guide on improving sleep hygiene.
Sadly, there’s no magic number for the ideal duration of sleep – it depends on many factors unique to each and every one of us. Plus, a truly restorative slumber involves smoothly transitioning through the sleep cycles. This means the best measure has to be the amount of sleep that allows you to wake refreshed, well-rested and able to perform well the following day.
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