How many hours sleep do you really need?

How many hours sleep do you really need?

18 January 2022

Dr Monique Hope-Ross and Dr Paul B Chell


We willingly give up our sleep, something quite unique to humans. What does your pet do when you are out? As you toil for their supper, they will be fast asleep, enjoying the comforts of your home! Animals have a natural rhythm, and this tells them when to sleep and when to wake; unlike humans, animals listen to their circadian rhythm. And wild animals don’t, unlike humans, get metabolic diseases!

It has been considered an elite activity to be able to work, live and play with little sleep, in fact quite macho. Sleep is for wimps etc! Aristotle Onassis famously said “don’t sleep too much. If you sleep 3 hours less each night for a year, you will have an extra month and a half to succeed in.” Onassis died at the age of 69. The tide is turning on this opinion and there is an increasing realisation that that those of us who don’t sleep enough, end up paying for this with our health.

The world is giving up its sleep and during the recent pandemic, our sleep has been severely curtailed, even without long COVID. 1 2 3 4 We are not sleeping enough and have lost approximately 20% of our sleep in the recent past. Sleep poverty affects our health, our immunity, and even our weight! And some simple steps will help us improve our sleep and boost our resistance to COVID. Understanding what makes us sleep, how it matters and the importance of the quality of sleep will help us to take the necessary steps to better sleep.

A planet in space Earthrise

Why do I need to Sleep?

We are rhythmical beings, responding to the rotation of the earth around the sun and on its axis, the light-dark cycle of life. We evolved to be part of this cycle and our bodily processes are cyclical. Sleep is a big part of the cycling of these processes. Some things happen at night when we are asleep and some things happen during the day; your body doesn’t like to digest food at night, and a full stomach makes it hard to get to sleep. Digestion is a daytime activity, and it conflicts with vital reparative night-time activities. And this conflict has metabolic consequences, with insulin resistance, leptin resistance and weight gain.

Your body is busy focussing on helping you to be the best during the day and it doesn’t have time for maintenance when it is busy thinking, moving and exercising. Growth, repair and maintenance happen at night and if you miss the repair cycle at night, it becomes harder and harder to be at your best. Lack of repair means accelerated ageing, poor immunity, insulin resistance and you become more susceptible to diseases, both infectious diseases such as COVID, as well as metabolic diseases such as by diabetes. A poorly maintained body is an old body! Small wonder that people age differently!

Sleep is needed for Repair, Growth and Regeneration

Sleep is the time when you regenerate after your day. Repair and growth ready you for the following day. After an hour of lifting weights, it is during the following night’s sleep, that growth hormone organises the repair process. Then your damaged muscles grow back bigger and stronger. But you do need to sleep for the growth!

Sleep is needed for Memory

Your brain needs to sleep too, as it consolidates memory at night. Your brain processes the day’s events, catalogues the goings on, and sends memory files from short-term storage to long-term storage memory files. Sleep less and you will have a poor memory and a higher risk of developing dementia.

How much Sleep do I need?

Those who sleep less, live shorter lives, an undeniable scientific fact. But just how many hours of sleep do we need? Sleep scientists are much closer to agreement on this. The consensus is that you need to sleep between 7-9 hours per night. Of course, there are some people who are outside these norms, but ideally a minimum of 7 hours is the sweet spot, and you should aim to make this 7 hours your minimum sleep time.

Alarm bells should ring if you regularly sleep less than 6 hours a night. The risk of insulin resistance, obesity and cardiovascular diseases increases, and your memory may not be as good as it could be. Lack of sleep disturbs your metabolism and is strongly associated with weight gain.

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What does Quality of Sleep mean?

Not just does the amount of sleep matter, but the quality of sleep is also important, as different things happen in the different cycles of sleep. There are four different stages or cycles of sleep, and you move smoothly from one stage to the next. Each cycle lasts for about 90-120 minutes, and in health there are normally 4 cycles per night.

The cycles are composed of varying combinations of both REM (rapid eye movement) and non-REM (non-rapid eye movement) sleep. If you lose two hours of sleep, you lose an entire cycle! REM sleep is deep sleep when dreams occur. During REM sleep, your muscles go limp. That’s why, unlike most animals, sleeping in trees is a bad idea!

The amount of non-REM sleep and REM sleep in each cycle is carefully allotted, throughout the night. The proportion of REM versus non-REM sleep changes within each cycle and later in the night the amount of REM sleep increases. The right amount of REM sleep is critical for memory and lack of REM sleep badly affects memory. And that’s a big problem when sleep is shortened. Losing two hours sleep in the morning robs you of vital REM or memory building sleep.

The quality of sleep means appropriate cycling of the REM and non-REM sleep throughout the four nightly cycles.

Alcohol reduces REM sleep significantly. Thus, alcohol robs you of the restorative type of sleep, with failure of memory processing. Delirium tremens, seen in alcoholics who stop drinking abruptly, is due to spill over of dreams to the waking state, secondary to a long-term lack of REM sleep. 2

What gets you to sleep?

Sleep is the final crescendo of the world’s greatest orchestra, a well-oiled machine with key players having specific timing and roles. Get one note out of place and the whole piece disintegrates. The master clock, melatonin and our body clocks are all key players in your sleep orchestra. Body clock harmony is the key. Dyssynchronous body clocks mean fractured, poor sleep: a disharmonious and sad melody.

Melatonin is the starting Gun of Sleep

Our good friend melatonin, called the ‘hormone of darkness’ chimes the sleep bell. Melatonin, is the trigger for sleep, and tells you that it is time to go to sleep.5 In the early evening, after dusk, the level of melatonin starts to build up and when it reaches a certain point, the brain dictates that sleep is now to be generated. And then you fall asleep. As you sleep and the night turns to dawn, the level of melatonin drops and cortisol starts to increase, which increases your heart rate, your blood pressure and temperature, preparing you for the day and then you wake up. When you wake up, the circulating melatonin has disappeared.

Chart showing Melatonin over a 24 hour period

The whole process starts again in early evening, with a rise in melatonin. But melatonin calls the time and then your brain generates sleep. Synchronous body clocks are the key to this magical scenario.

Melatonin is made in the pineal gland, a gland deep in your brain and it is then released into the blood stream. It is made from tryptophan, an essential amino acid, that we can’t manufacture. We can find tryptophan in good amounts in eggs, milk, chicken, turkey, cheese, tuna, nuts and seeds. You need to eat tryptophan every day to supply this essential building block of melatonin and don’t forget that you need tryptophan to make your happy hormone serotonin too!

The Master Clock

The Master Clock controls the timing of your body clocks. The master clock is set by morning daylight. Every single morning, your master clock, resets each of your 31 trillion body clocks. And because of this, all your clocks chime in synchrony.

And the master clock is instrumental is setting up your sleep for that night. It stimulates the timely production of melatonin to get you to sleep. It stimulates growth hormone to do the night-time building and repairs, and cortisol release in the early morning to help you to get up and face the day.

Should the body clocks chime at a different time to the master clock, things don’t happen in the right order and body processes become disordered. This spills over into sleep, causing problems getting to sleep, and staying asleep. Clock dyssynchrony is a cause of much ill-health, including insulin resistance, obesity and associated with long COVID.

Those people who have regular good quality sleep are the lucky ones, rewarded by good health. If you don’t sleep well, can anything be done? The answer is definitely YES. No one doubts that they can get fitter by following a good fitness programme and the same is true of sleep. Sleep hygiene and attention to small details, will help to improve your sleep significantly, and this will reap dividends in terms of your metabolism, weight and health.6

Read more tips in our blog post: How to Sleep Better

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The information on this website is not intended to constitute medical advice, nor is it intended to replace or conflict with the advice given to you by your doctor or other health professional. Before embarking on the plans set out on this website, you should discuss them with your doctor, especially if you have any medical condition or if you are taking any medication. The author and publisher disclaim any liability directly or indirectly from the use of the material in our books and on our website by any person.

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