How many hours sleep do you really need?

How many hours sleep do you really need?

Published: 18 January 2022

Updated and medically reviewed: 29 October 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 are fast asleep, enjoying the comforts of your home! Animals have a natural circadian rhythm, and this tells them when to sleep and when to wake up; unlike humans, animals listen to their circadian rhythm and they benefit from this with better health.

It was 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” but Onassis died at the age of 69. So much for that. 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.

Sleep under 6 hours and you will have a shorter life

We have lost approximately 20% of our sleep in the recent past. The world is giving up its sleep and during the recent pandemic, our sleep was 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 to improve both our sleep and our health. 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
Figure 1. Eathrise, courtesy of NASA

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. Digestion is a daytime activity, and repair is a night-time activity, it is difficult for us to do both at the same time. Late-night eating conflicts with your natural circadian rhythm, making it hard to get to sleep and preventing vital repair processes. This conflict between day-time and night-time activity has health consequences, which leads to the development of insulin resistance, weight gain and other metabolic diseases.

Your body is busy focussing on helping you to be your 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 many metabolic diseases such as by obesity and diabetes. A poorly maintained body is an old body! It is 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 a weight lifting session, when you are asleep that night, growth hormone organises the muscal repair and regeneration of your muscles. Your damaged muscles grow back bigger and stronger. But you do need to sleep for this to happen!

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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Seven hours is the minimum sleep needed for health.

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 4-5 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 of sleep, with severe health consequences!

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 with each cycle. Early in the night non-REM sleep predominates and later in the night this reverses with an increased amount of REM sleep as the night goes on.

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.

REM sleep is deep sleep when dreams occur. During REM sleep your muscles go limp. That's why sleeping in trees is a bad idea! 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. If one note is out of place, the entire piece disintegrates. The master clock, melatonin, adenosine and your body clocks are all key players in your sleep orchestra. Body clock harmony and a healthy circadian rhythm is the key. Dyssynchronous body clocks mean fractured, poor sleep: a disharmonious and sad melody.

Melatonin is the starting Gun of Sleep

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. It 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 you can’t manufacture yourself. You 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 your body clocks chime at a different time to your 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

Please read: 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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We're here to share information about how to lose weight quickly, become healthier and leaner, stay lean, feel better and live longer.

Please read: 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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