Cookies on the Bupa website

We use cookies to help us understand ease of use and relevance of content. This ensures that we can give you the best experience on our website. If you continue, we'll assume that you are happy to receive cookies for this purpose. Find out more about cookies



The science of sleep

We spend about a third of our life asleep but have you ever thought about why you sleep? And how much you should be getting?

Here we explain the science behind sleep to give you a better understanding of this most fundamental of needs.

Slippers by a bed


  • Why do I need to sleep? Why do I need to sleep?

    Sleep is a bit of a mystery. We still don’t fully understand why we need to sleep and this has long been the subject of debate. There are several theories but the two that seem to stick are that sleep:

    • allows your body to replenish energy stores and repair itself
    • gives you the chance to save energy

    Sleep may also aid learning and give our bodies time to organise all the memories of the hundreds of events we experience every day.

    Did you know...?

    We know much more about the effects of not getting enough sleep. It’s associated with less concentration and feeling tired and irritable, as well as depression. This suggests sleep is important for our brains to work properly.

    Bupa Health Assessments

    Find out how a Bupa health assessment can help you understand your health and identify future health risks

  • How much sleep do I need? How much sleep do I need?

    The amount of sleep we need changes as we get older, and it’s also a personal thing – some of us need more than others. As long as you’re feeling refreshed and alert the next day, you’re probably getting enough.

    Although there is no magic number of hours, here’s a general guide for how much sleep you need.

    Stage of life Hours
    Babies 17
    Toddlers 12 to 14
    Children 9 to 12
    Teenagers 9
    Adults 8
    Older adults 8

    Did you know...?

    It’s common for teenagers to stay up late and complain about feeling too tired to get up for school but there may be some biological theory behind this. Some teenagers get a condition called delayed sleep phase disorder in which their body clock doesn’t work properly. They have a natural inclination to go to bed late and wake up later than is considered normal.

  • Why do I fall asleep? Why do I fall asleep?

    You might not have given much thought to what causes you to fall asleep but there are various chemical processes in your body at work. Some of these keep track of how long you’ve been awake and when you need to sleep. Others determine what time of day is best to sleep. These processes interact with each other and with your environment to make you feel sleepy at about the same time every day.

    You also have an internal body clock, which is governed by daylight. Cells in your eyes detect this and stimulate your body to produce a light-sensitive chemical called melanopsin which makes you feel awake in the daytime. As it gets darker, less of this chemical is produced and instead your body produces something called melatonin which makes you feel sleepy.

    Did you know...?

    Your internal body clock isn’t fully developed when you’re first born. This goes some way to explaining the sleepless nights many new parents know only too well. It develops it in the first few months of your life and then you gradually adjust to sleeping more at night than during the day.

  • An overview of your health

    Find out how a Bupa health assessment can help you understand your health, identify future health risks, and offer practical advice for a healthier you.

  • What happens when I go to sleep? What happens when I go to sleep?

    You pass through different phases of sleep in regular cycles during the night. The two main phases are:

    • rapid eye movement (REM) sleep
    • non-rapid eye movement (non-REM) sleep

    You move through stages of non-REM sleep then into REM sleep and back again. Each full cycle takes about one to two hours.

    The sleep cycle

    Click on the image to enlarge it.

    The sleep cycle

    Did you know...?

    Active dreams and nightmares can start to be a real problem for toddlers. It’s a good idea to take some practical steps to try to prevent your child having nightmares. So, for example, it might sound obvious but make sure your toddler doesn’t watch anything frightening on television before they go to bed.

  • Why can't I sleep? Why can't I sleep?

    It’s normal to wake up during the night every couple of hours for a minute or so. You won’t usually be aware of these brief interruptions to your sleep. But if you’re disturbed by something when you wake up – maybe your partner snoring – it may make it harder to go back to sleep. These breaks in your sleep may also become more noticeable if you’re feeling anxious about something.

    If this becomes a regular problem and you start to get insomnia, you’ll feel tired during the day. For tips on how to tackle this, see our article How to get a good night’s sleep.

    Did you know...?

    We get less deep sleep as we get older so can wake more easily after the first three to four hours of sleep. Other health issues may also have an impact on the amount and quality of sleep you get. For example, if you’re in pain from osteoarthritis.

  • Resources Resources

    Headspace This tool describes itself as gym membership for your mind using meditation and mindfulness techniques. You can start off with free 10-day introduction to meditation and then choose to subscribe for access to more exercises covering a range of topics. You can use it on your phone or computer, depending on what suits you best.
    Mental Health Foundation The Mental Health Foundation is a charity that carries out research and offers information about many areas of mental health. If you have problems with your sleep, this page is for you. It has details of some reasons that are behind having trouble sleeping and suggestions of things you can try to help yourself sleep better.
    Mind The charity Mind has information to support people with a mental health condition and those who care for them. Their sleep content has tips on practical things you can do to help yourself if you’re not sleeping well.


    • Khan S, Heussler H, McGuire T, et al. Melatonin for non-respiratory sleep disorders in typically developing children (protocol). Cochrane Database of Systematic Reviews 2011, Issue 5. doi:10.1002/14651858.CD009141
    • Normal sleep, sleep physiology, and sleep deprivation. Medscape., published 22 October 2013
    • Sleeping well. Royal College of Psychiatrists., published July 2014
    • Insomnia. BMJ Best Practice., published 21 January 2015
    • Sleep problems in childhood and adolescence: for parents, carers and anyone who works with young people. Royal College of Psychiatrists., published January 2012
    • Gradisar M, Crowley SJ. Delayed sleep phase disorder in youth. Curr Opin Psychiatry 2013; 26(6):580–85. doi:10.1097/YCO.0b013e328365a1d4
    • Pineal gland and circadian rhythms. PatientPlus., reviewed 6 September 2013
    • Iwata O, Okamura H, Saitsu H, et al. Diurnal cortisol changes in newborn infants suggesting entrainment of peripheral circadian clock in utero and at birth. J Clin Endocrinol Metab 2013; 98(1):E25–32. doi:10.1210/jc.2012-2750
    • Clinical practice guideline on sleep disorders in childhood and adolescence in primary care. Ministry of Health Social Services and Equality., published 2011
    • Geriatric sleep disorder. Medscape., published 23 September 2014
  • Has our information helped you? Tell us what you think about this page

    We’d love to know what you think about what you’ve just been reading and looking at – we’ll use it to improve our information. If you’d like to give us some feedback, our short form below will take just a few minutes to complete. And if there's a question you want to ask that hasn't been answered here, please submit it to us. Although we can't respond to specific questions directly, we’ll aim to include the answer to it when we next review this topic.

    Let us know what you think using our short feedback form
  • Related information Related information

  • Author information Author information

    Reviewed by Rachael Mayfield-Blake, Bupa Health Content Team, August 2015.

About our health information

At Bupa we produce a wealth of free health information for you and your family. We believe that trustworthy information is essential in helping you make better decisions about your health and care. Here are just a few of the ways in which our core editorial principles have been recognised.

  • Information Standard

    We are certified by the Information Standard. This quality mark identifies reliable, trustworthy producers and sources of health information.

    Information standard logo
  • HONcode

    This site complies with the HONcode standard for trustworthy health information:
    verify here.

    This website is certified by Health On the Net Foundation. Click to verify.

What our readers say about us

But don't just take our word for it; here's some feedback from our readers.

Simple and easy to use website - not alarming, just helpful.

It’s informative but not too detailed. I like that it’s factual and realistic about the conditions and the procedures involved. It’s also easy to navigate to areas that you specifically want without having to read all the information.

Good information, easy to find, trustworthy.

Meet the team

Nick Ridgman

Nick Ridgman
Head of Health Content

  • Dylan Merkett – Lead Editor
  • Graham Pembrey - Lead Editor
  • Laura Blanks – Specialist Editor, Quality
  • Michelle Harrison – Specialist Editor, Insights
  • Natalie Heaton – Specialist Editor, User Experience
  • Fay Jeffery – Web Editor
  • Marcella McEvoy – Specialist Editor, Content Portfolio
  • Alice Rossiter – Specialist Editor (on Maternity Leave)

Our core principles

All our health content is produced in line with our core editorial principles – readable, reliable, relevant – which are represented by our diagram.

An image showing or editorial principals

                  Click to open full-size image

The ‘3Rs’ encompass everything we believe good health information should be. From tweets to in-depth reports, videos to quizzes, every piece of content we produce has these as its foundation.


In a nutshell, our information is jargon-free, concise and accessible. We know our audience and we meet their health information needs, helping them to take the next step in their health and wellbeing journey.


We use the best quality and most up-to-date evidence to produce our information. Our process is transparent and validated by experts – both our users and medical specialists.


We know that our users want the right information at the right time, in the way that suits them. So we review our content at least every three years to keep it fresh. And we’re embracing new technology and social media so they can get it whenever and wherever they choose.

Our accreditation

Here are just a few of the ways in which the quality of our information has been recognised.

  • The Information Standard certification scheme

    You will see the Information Standard quality mark on our content. This is a certification programme, supported by NHS England, that was developed to ensure that public-facing health and care information is created to a set of best practice principles.

    It uses only recognised evidence sources and presents the information in a clear and balanced way. The Information Standard quality mark is a quick and easy way for you to identify reliable and trustworthy producers and sources of information.

    Certified by the Information Standard as a quality provider of health and social care information. Bupa shall hold responsibility for the accuracy of the information they publish and neither the Scheme Operator nor the Scheme Owner shall have any responsibility whatsoever for costs, losses or direct or indirect damages or costs arising from inaccuracy of information or omissions in information published on the website on behalf of Bupa.

  • British Medical Association (BMA) patient information awards

    We have received a number of BMA awards for different assets over the years. Most recently, in 2013, we received a 'commended' award for our online shared decision making hub.

Contact us

If you have any feedback on our health information, we would love to hear from you. Please contact us via email: Or you can write to us:

Health Content Team
Battle Bridge House
300 Grays Inn Road

Find out more Close

Legal disclaimer

This information was published by Bupa's Health Content Team and is based on reputable sources of medical evidence. It has been reviewed by appropriate medical or clinical professionals. Photos are only for illustrative purposes and do not reflect every presentation of a condition.

The information contained on this page and in any third party websites referred to on this page is not intended nor implied to be a substitute for professional medical advice nor is it intended to be for medical diagnosis or treatment. Third party websites are not owned or controlled by Bupa and any individual may be able to access and post messages on them. Bupa is not responsible for the content or availability of these third party websites. We do not accept advertising on this page.

For more details on how we produce our content and its sources, visit the 'About our health information' section.

ˆ We may record or monitor our calls.