Why Sleep Is Important

Why Sleep Is Important

13 min read

Dr Suresh Khirwadkar

Sleep is important. Very important. It is important for all manner of reasons, some that are obvious - if you don't sleep you feel tired. Others that are perhaps less well known - DNA repair.

That's right. Sleep is where you repair your body. DNA repair. Cellular repair. Repairing wounds, both physical and mental.

How much sleep do we get?

Humans on average, like many other animals, spend approximately one third of their life asleep. By the time you make it to 90 years old, you will have spent roughly 30 years of it asleep! That's quite a lot of time spent on something that was for a long time thought to be a passive process that merely 'happened'.

Given the amount of time we spend doing it, it's amazing we spend such little time studying it or trying to perfect it.

We spent countless hours in the gym, working on our diet, working on our mental health and other physical health issues, as we should, but then often we completely neglect our sleep.

How much should we get?

There is no set figure, though studies demonstrate that sleeping for fewer than 5 hours a night is associated with adverse outcomes. Too much sleep can also cause issues, though there is no obvious figure for this.

It is estimated that over two thirds of us will suffer from sleep issues in our life, in fact as many as 80% of us might struggle with our sleep. This can range from mild insomnia to severe nacrolepsy.

Despite there being no set time that is thought to be optimal, it is estimated that we should be aiming for between 7-9 hours of sleep on average to wake feeling refreshed. Some groups will need less or more than this.

Why do we need sleep?

Despite all of our advances in modern medicine, this is not terribly well understood. We all know the downsides of not sleeping, but few will know the benefits of a proper night's sleep. Sleep is important for a number of reasons beyond the obvious not feeling tired:

  • DNA repair
  • Cellular repair
  • Wound healing
  • Hormone regulation
  • Hunger management
  • Immune system regulation
  • Memory and concentration
  • Brain and muscle development

What happens if we don't get enough sleep?

You will feel tired. We all know this of course, but progressive nights of poor sleep will lead to worsening fatigue and tiredness, ultimately resulting in reduced ability to concentrate and poor memory. Decision-making ability will also be affected, as are reactions and our ability to think clearly.

In fact, being awake for around 17 hours is the equivalent of having a blood alcohol level (BAL) of around 0.05 (the legal limit in Australia). Being awake for 24 hours is the equivalent of a BAL of 0.1 - i.e. if you were to drive it would be like you are over the limit. Wow. I wonder how many of us know that?

Other issues from poor sleep include:

  • Lower immune system
  • Fatigue and lethargy
  • Weight gain
  • Increased risk of injuries
  • Worsening of mental health
  • Increased appetite
  • Memory impairment
  • Increased risk of chronic diseases

There is a concept coined The Sleep Debt that refers to the 'debt' we raise when we are awake. One that must be repaid with sleep. If we do not repay that debt, then like any debt it accrues interest. Unlike your home loan though this one accrues that debt at an alarming rate, and eventually the body will ring it in and demand payment.

If you do not repay it with sleep, then it will take from you in other ways - all the ways we have already outlined.

How does poor sleep increase the risk of weight gain?

Sleep is important for regulating numerous hormones with the body, and some of these also are heavily involved our regulation of body weight, fat levels, and appetite.

Leptin is a hormone that is primarily regulated through sleep, and is involved in the feeling of satiety - i.e. it makes you feel fuller quicker. It has other roles as well. Poor sleep leads to disordered leptin levels within the body and can lead to over-eating, and thus, weight gain.

Cortisol - we discussed this briefly in the Insulin Resistance article - but cortisol is highly involved in weight regulation within the body, as well as immune function. A disordered cortisol level is highly associated with weight gain, obesity, hypertension, heart disease, type 2 diabetes, and numerous other chronic diseases. In fact shift workers are at quite an increased risk of chronic diseases, possibly through disordered cortisol levels due to shifting sleep patterns.

Ghrelin - a hormone that causes hunger. Disordered sleep leads to disordered release and regulation of Ghrelin, which can lead to increased hunger levels and reduced satiety (the feeling of fullness).

Poor sleep is very strongly associated, if not causative for weight gain and obesity.

Whilst it could be a confounder, studies have demonstrated it is more likely that it is further compounded because many individuals that have poor sleep also have other poor health behaviours such as lack of exercise, poor diet and nutrition, worse mental health and more stress - which leads to further weight gain. Which leads to further weight issues.

It is for this reason that when I see patients for weight loss I also discuss and assess their sleep and make a plan for fixing their sleep issues, as without this, weight loss is very difficult and not likely sustainable in the long term.

What is normal sleep?

We normally have 5 states of sleep

  • Stage 1 - Very light sleep
  • Stage 2 - Light / transitional sleep
  • Stage 3 - Deep sleep
  • Stage 4 - Deepest sleep
  • Stage 5 - REM sleep (where we dream)

This is one cycle.

Most people will have 4-5 cycles per night.

Whilst they are all important, the most important stage is perhaps REM sleep, and we know that not enough REM sleep will incur a cost, usually in the form of disordered thinking, memory impairment and poor concentration the following day.

What leads to poor sleep?

There are many reasons why you might suffer with sleeping difficulties, and it is important to speak to your doctor to discuss your issues. There could be a genuine medical issue such iron deficiency, restless leg syndrome, or obstructive sleep apnoea. These are relatively easy to diagnose and usually straightforward to manage.

if you think you might have sleep apnoea (e.g. if you stop breathing over night or make lots of funny noises over night) then please fill out a Epworth Sleepiness Score and STOPBANG questionnaire - on my files page

There may also be more serious issues that could affect your sleep such as mental health issues, particularly trauma or severe anxiety and you must see your doctor to discuss these.


Despite many people using alcohol to help them sleep, unfortunately there is a negative association with alcohol and sleep. Despite a drink of alcohol is often used to help somebody to get to sleep (a nightcap) - all because alcohol can induce sleep a little earlier - it can have a serious negative effect on the quality of sleep.

Evidence shows that having a drink in the hour before sleep can disrupt stage 2 - light sleep. Even alcohol within 6 hours of sleep can have a negative effect.

Of course the more alcohol we have, the greater the effect will be, to the point where if you have had too much alcohol you may fee that you haven't even slept - because basically your brain hasn't really.

Alcohol can also cause a rebound wakefullness - i.e it can make you wake up, and reduce your ability to return to sleep.

Exercise and inactivity

There is a complex relationship between sleep and exercise, one that still is not well understood. Evidence shows that usually exercise in the daytime will improve sleep, and exercise in the evening will reduce sleep. However for individuals who are used to this pattern, or those who are highly active otherwise, the reverse may be true - they may get better sleep if they exercise in the evening.

Exercise during the day time has also been shown to extend the deep stages of sleep (3-5), likely leading to a 'better quality' sleep.

Excessive exercise has the converse effect and can reduce the quality of sleep, as well as quantity. There are no clear guidelines on what is considered excessive for this purpose though.


Not specifically a condition in its own right, more of a symptom, insomnia is defined as difficulty getting to, or staying asleep, waking up during the sleep cycles usually for 3 months or more. Short term, or transient insomnia may be diagnosed prior to 3 months.

It can be triggered by any number of issues, but transient insomnia is usually caused by

  • stress
  • temporary illness
  • alcohol excess
  • caffeine
  • excitement
  • travel
  • environmental factors (e.g. hot/cold)

For short term, non-chronic insomnia, medications may be an appropriate treatment as long as other factors are excluded, however for chronic insomnia (2 weeks or longer) medications are usually not the first line treatment as they do not address the underlying issues causing poor sleep. They also have side effects, and can be associated with adverse outcomes for the patients. In fact Benzodiazepines, often given to help sleep, are associated with an increased risk of sudden premature death in 18-55 year olds, and a risk of medication overdose and Dementia in older patients.

For chronic Insomnia, the first line therapy that is recommended is Cognitive Behavioural Therapy for Insomnia (CBTi). This is often delivered in digital format, so you may see it expressed as dCBTi.

It is often delivered electronically as CBTi practitioners are relatively few and far between as it quite a specialised area.

There are a few online providers of this, but I particularly recommened ThisWayUp which at time of writing was available free. It can also be prescribed by myself as part of a consultation and patient can access it free of charge this way.

Sleep apnoea

We touched on this briefly above, but there are 2 types:

  • obstructive
  • central

Obstructive Sleep Apnoea (OSA)

This is a condition in which sufferers tend to stop breathing at random intervals whislt asleep, or at least they struggle with their breathing whilst asleep. It occurs because the airway has become obstructed, hence the name obstructive sleep apnoea.

It is usually worse when patients are over weight, particularly if they are carrying a lot of weight on their chest or around their neck (neck circumference > 40cm is a point on the STOPBANG questionnaire), and is usually worst when laying on the back.

Patients with OSA may also move around a lot at night time, or kick or thrash in bed. This can also be due to Restless Leg Syndrome.

Central Sleep Apnoea (CSA)

Similar, but diferent to OSA. In CSA it is not so much a physical obstruction like in OSA, more so the brain is not sending proper signals to the body and it 'forgets to breath'. This condition is not particularly helped with weight loss and requires positive airway pressure (e.g. CPAP mask).

Restless Leg Syndrome (RLS)

A condition characterised by repeated, sometimes painful movement of the legs at night time, but it can occur at any point in the day. It can be very unpleasant, sometimes painful, and occurs typically when sitting or laying down. Moving the legs may temporarily relieve the urge to move the legs.

It is diagnosed usually from clinical symptoms in a consultation with your doctor, but may be subtle and so sometimes a 'trial of treatment' may be suggested. A positive trial of treatment can be then confirm the diagnosis.

If you suspect your have RLS you should consult your doctor as you may have other health issues such as iron deficiency or nerve problems that may be the cause.

How does light affect sleep

Both positively and negatively. The effects of light on sleep are still poorly understood and further reserarch is required. We do know that blue light can have an impact on sleep, in both quality and quantity, as can non-blue light, but the relationship is complex.

It is a whole topic in itself so I cannot do it justice here, but briefly:

  • Blue light within a few hours may significantly reduce the ability to get to sleep and stay asleep
  • Blue light in the morning may aid waking and can improve the sleep - wake cycle
  • Strong bright light in the morning, day time and early evening usually has a positive effect on sleep and is often recommended for patients with insomnia - e.g lightbox therapy
  • Getting an hour a day of bright sunshine, even daylight on an overcast day will do, can improve your sleep

How do you treat sleep problems?

It very much depends on the cause of the sleep issue, and this is why if you have sleep problems for more than a few weeks you should consult your doctor. We have touched on some of the treatments already, but broadly speaking:

  • Reduce alcohol
  • Reduce evening caffeine
  • Increase day time exercise
  • Increase morning, day time and early evening bright light
  • Reduce evening / night time blue light (e.g. night mode on devices)
  • Sleep hygiene training
  • Sleep Stimulus Control training
  • CBT for insomnia (CBTi)
  • Sleep environment review (considered in Sleep hygiene / sleep stimulus)
    • Ensure a proper temperature in the bedroom/sleep environment
    • Keep the bed/bedroom for sleep/sex only
    • Appropriate thickness of bed covers and sheets
    • Comfortable sheets
    • Body temperature regulation (and why pyjamas are useful vs sleeping naked)
    • Control noises
    • Minimise light in the bedroom at night

Sleep can be a particular problem for many patients, and I would urge you to consult with your doctor if you have difficulties sleeping, particularly if they are continuing for more than 2 weeks as this can have significant complications for your health.

For patients wishing to consult with me I would recommend if possible bring an Epworth Sleepiness Score and a STOPBANG questionaire with you to save time, though that is not required.

If you have not already done so, I would also recommend that you read my article on insulin resistance and weight loss as sleep is particularly important for these as well.

Dr Suresh Khirwadkar is a Lifestyle GP specialising in all aspects of Lifestyle Medicine, Weight Loss, Primary Care, Skin Cancer and Psychology. He did his undergraduate and post graduate training in the UK, currently practices in Australia and holds MBChB, BSc (HONS), MRCGP, FRACGP
Copyright 2022 Dr Suresh Khirwadkar
Disclaimer: Results are not guaranteed and can vary. Please speak to your Doctor about the most appropriate treatment for your medical conditions