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Monday’s medical myth: you need eight hours of continuous sleep each night

We’re often told by the popular press and well-meaning family and friends that, for good health, we should fall asleep quickly and sleep solidly for about eight hours – otherwise we’re at risk of physical…

Waking up in the night is perfectly normal. planetchopstick

We’re often told by the popular press and well-meaning family and friends that, for good health, we should fall asleep quickly and sleep solidly for about eight hours – otherwise we’re at risk of physical and psychological ill health.

There is some evidence to suggest that those who consistently restrict their sleep to less than six hours may have increased risk of cardiovascular disease, obesity and diabetes. The biggest health risk of sleep deprivation comes from accidents, especially falling asleep while driving.

Sleep need varies depending on the individual and can be anywhere from 12 hours in long-sleeping children, to six hours in short-sleeping healthy older adults. But despite the prevailing belief, normal sleep is not a long, deep valley of unconsciousness.

The sleep period is made up of 90-minute cycles. Waking up between these sleep cycles is a normal part of the sleep pattern and becomes more common as we get older.

It’s time to set the record straight about the myth of continuous sleep – and hopefully alleviate some of the anxiety that comes from laying in bed awake at night.

So what are the alternatives to continuous sleep?

The siesta

The siesta sleep quota is made up of a one- to two-hour sleep in the early afternoon and a longer period of five to six hours late in the night. Like mammals and birds, humans tend to be most active around dawn and dusk and less active in the middle of the day.

It’s thought the siesta was the dominant sleep pattern before the industrial revolution required people to be continuously awake across the day to serve the sleepless industrial machine. It’s still common in rural communities around the world, not just in Mediterranean or Latin American cultures.

Our siesta tendency or post-lunch decline of alertness still occurs in those who never take afternoon naps. And this has less to do with overindulging at lunchtime and more to do with our circadian rhythms, which control our body clock, hormone production, temperature and digestive function over a 24-hour period.

Night Heron

Bi-phasic sleep

Historical records also suggest that a segmented or bi-phasic sleep pattern was the norm before the industrial revolution. This pattern consists of an initial sleep of about four and a half hours (three sleep cycles of 90 minutes each) followed by one to two hours of wake and then a second sleep period of another three hours (another two sleep cycles).

During the winter months, northern Europeans would spend nine or ten hours in bed, with two to three hours of it spent awake, either in one long mid-night period or several shorter wake periods across the night.

The bed was the cheapest place to keep warm and was considered a place of rest as well as sleep. A few hours of wakefulness certainly wouldn’t have been considered abnormal or labelled as insomnia.

Can’t sleep? Don’t worry

These days we expect to have close to 100% of our time in bed asleep, dozing off within minutes and not waking at all until the alarm sounds. Unfortunately this myth sets us up for worry if we find ourselves awake in the middle of the night. And this worry can lead gradually to the development of insomnia.

Humans can sleep on very different schedules, with little difference in wakeful competence. International sleep researchers have trialled a number of different sleep schedules: sleep for 20 minutes every hour; one hour sleep every three hours; ten hours sleep every 28 hours. Participants survive easily on all these schedules despite their impracticality in our 24-hour world.

The best quality sleep is obtained during our circadian low phase – when body temperature and metabolic rate are at their lowest. For most people, this occurs late at night. But just like other species, humans can be opportunistic sleepers and satisfy our need for sleep when we get the opportunity.

There’s no doubt that the eight-hour solid sleep myth is a relatively recent cultural imposition. And although it satisfies our modern lifestyle, it does have its disadvantages.

Some have lamented the loss of wakefulness between sleep cycles as a valuable time of contemplation or creativity.

But probably the greatest negative impact of the eight-hour sleep myth is its power to create insomniacs out of good sleepers who experience normal awakenings across the night.

Join the conversation

12 Comments sorted by

  1. Susan McCosker

    Former school teacher

    In line with the idea that all adults need eight straight hours of sleep, we also have an idea that babies and toddlers need a certain amount of sleep, and if they aren't getting it then there is a problem that needs fixing!

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  2. Daryl Adair

    Associate Professor of Sport Management at University of Technology, Sydney

    Nearly a year ago I was diagnosed with sleep apnea. I now have a CPAP machine that keeps my airways open during the night. It does not bother me at all. And I wake up refreshed. I feel ten years younger - mentally and physically. Although some people may need less sleep than is commonly assumed, the quality of that sleep is (obviously) paramount. This does not contradict your article at all; it just adds another dimension to discussions about quality (as opposed merely to quantity) of sleep.

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  3. Dale Bloom

    Analyst

    Having carried out shift work for many years, I found the worst time was from about 4.00 am to about 5.00 am. The body would often seem to shut down during that time, (i.e. The eyes could be open, but physically the body could be semi-asleep). By about 6.00 am, I would be fully awake again.

    I am wondering if this is true for most other people, and if so, that period of time may be an important period for safety reasons in many companies.

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    1. Grendelus Malleolus

      Senior Nerd

      In reply to Dale Bloom

      Dale, there has been quite a lot of work over the years looking at hours of the day and wakefulness and there are certainly a number of studies that suggest thwt the period of early morning is indeed associated with decreased alertness. This study: http://oem.bmj.com/content/53/11/767.full.pdf shows a graph that includes that 4-5am period, and guess where the least alertness was experienced - right in that zone.

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  4. Katrina Grant

    Art Historian

    Thanks for this, I have always woken up several times a night and either stay awake or fell asleep again, the idea that I am sleeping in 90 minute cycles make perfect sense.

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  5. Russell Walton

    Retired

    Very reassuring, when I asked my GP, I was was informed 8 hrs overnight was the optimum. I'm nearly 70 and sleep 5-6 hrs at night with the occasional afternoon siesta.

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  6. Dianna Arthur

    Environmentalist

    I agree with the siesta, unfortunately, employers don't and in fact view working long hours as preferable - while not taking into the equation the quality of the work done.

    As someone who has fibro myalgia I am very sensitive to the above lack of logic.

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    1. Dianna Arthur

      Environmentalist

      In reply to Dianna Arthur

      In addition to my comment above. Before I became ill with FM, I was one of those early morning risers. I practically leapt out of bed, took the dog for a run, had a hearty breakfast and was generally regarded as an irritating git.

      Oh happy days. Now I can never get enough sleep.

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  7. Ben Moore

    Lecturer, Hawkesbury Institute for the Environment, University of Western Sydney

    It's reassuring to know that we're "like mammals"!

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  8. Alex A. Sanchez

    Post-Doc in Clinical Psychology

    Another factor that is not discussed in the article is age. As we age, it becomes more difficult to sleep for long, uninterrupted periods. While 8 hours of sleep may be the idea for developing bodies and minds, the older adult body does not have the same physical requirements and a varied sleep schedule may be more appropriate.

    One reason that 8 continues hours is recommended may come from research (I don't have a source off-hand) that suggests memory is markedly improved during the day after the subject has had over 7 continuous hours of sleep the night before. Again, this is a benefit appropriate for a young developing brain (and school-aged kids), and not necessarily a practiced expert with a specialization.

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    1. Judith Olney

      Ms

      In reply to Alex A. Sanchez

      I find I need around 7 hours sleep per 24 hours, although I have my most refreshing sleep between 5am and 8am. This has always been the case for me, but unfortunately it is not ideal for many jobs in our society. When having to wake early for work I found that I was chronically sleep deprived, and my overall health suffered greatly. Going to bed earlier in the evening often made this worse, and was no help at all.

      There is also the perceived 'morality' of sleeping in the morning and being up later…

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