Research also shows that we are not aware of our own level of impairment.
In the long term, short sleep can lead to health problems.
Those who get less than six hours' sleep a night have a higher risk of putting on weight, developing type 2 diabetes and heart disease, and suffering a stroke.
Fortunately, our national surveys of New Zealanders have shown that most of us do get between seven to nine hours' sleep on average.
Concerning, though, is that about a quarter of New Zealanders get six hours or less sleep each night.
Myth 2 - You can catch up on lost sleep at the weekend
Weekdays are full with work, family and social commitments, and sleep is often sacrificed.
Many of us aim to catch up on any lost sleep at the weekend.
However, research shows this is not as achievable as we think.
Missing out on sleep during the week leads to a continual decline in functioning.
Sleeping in on Saturday or Sunday leads to an improvement in this functioning, but we don't seem to return to the optimal levels we experience when we are getting seven to nine hours' sleep - even after two to three days of catch-up at the weekend.
Depending on how short we have been cutting our sleep, this can mean we start the next week with a sleep debt - and arrive at work behind the eight ball.
Myth 3 - Blasting cold air in your face will keep you awake if you're feeling sleepy while driving
There are plenty of strategies that we try to keep ourselves awake when driving.
These might include turning up the radio or blasting cold air in our faces. What we know is that these strategies work in the short term, but are not an effective way to keep yourself awake if you're feeling really sleepy.
The golden rule is, if you are too sleepy you will fall asleep uncontrollably. So the best strategy is to start your trip in the best possible position.
Get a full night's sleep before you go, drive during daylight hours to be most alert, and stop and take regular breaks.
If you are feeling drowsy while driving home from work, consider a short 20- to 40-minute nap before you head home and drink a cup of coffee 15 to 30 minutes before you leave to give yourself a brief caffeine kick. If sleepiness becomes overwhelming, stop as soon as you can and take a nap, or find another way to get where you're going.
Myth 4 - Waking up during the night means you're not getting good quality sleep
There is definitely a myth that waking up during the night means that your sleep is abnormally broken.
In fact, it is quite normal to wake overnight.
Historically, individuals would experience a longer sleep period following the natural day and night cycle, with a two-to-three hour period of wakefulness in the middle of the night between two sleep periods, without any impairment.
Importantly, people still obtained approximately eight hours' sleep in total each night.
In today's society, it is quite normal to wake one to three times overnight, roll over and go back to sleep.
Waking more frequently than this may mean there is something in your sleeping environment that is causing you to wake, or you may have a medical issue that is disrupting your sleep.
If you suspect the latter, have a chat with your GP.
Myth 5 - Older people need less sleep
Our sleep changes substantially across the lifespan.
As any parent will know, young infants need much more sleep than adults and have a mind of their own when it comes to a sleep routine.
As we progress through childhood, adolescence and adulthood, our sleep structure and timing continues to change.
The most dramatic changes are seen between birth and the end of adolescence.
While the sleep of older adults may be more broken and the structure of their sleep slightly different to younger adults, in general older adults still need seven to nine hours' sleep a night to function at their best.
Curiously, although older adults show clear impairment when they don't get enough sleep, they appear to be slightly more resilient to sleep loss than younger adults.
Myth 6 - The sleep habits of teenagers are the result of laziness
It is no secret that teenagers like to go to bed late and sleep in as much as they can each morning.
These habits are often attributed to laziness, but are actually a result of biological changes in the way the circadian body clock functions in teenagers.
In adolescence, our internal body clock shifts later relative to the natural day and night cycle, resulting in a biological preference for later bed and wake times.
The practicalities of this mean that teenagers are unable to fall asleep when they want to and find it difficult to get out of bed in the morning.
This, combined with increasing independence, social activity and school demands, can lead to short sleep on school nights.
Approximately 21 per cent of New Zealand teenagers do not get enough sleep - about eight or nine hours each night, compared with their biological sleep need, which is approximately nine to 10 hours.
Our studies on New Zealand teenagers have also highlighted that there is a large discrepancy between bed times on school nights (10.30pm) and weekends (midnight).
In the short term, insufficient sleep in teenagers leads to poor academic performance - poor memory, information processing and attention span - poor mood, and increased risky behaviour.
In the long term, it may lead to increased weight and cholesterol, as well as behavioural sleep habits that continue into adulthood.
Myth 7 - We don't know anything about the functions of sleep
It may be easier to justify cutting sleep short when it doesn't appear to have any particular function.
Many of us will have heard that it is more putting the body and brain into hibernation mode so that we can "rest".
This view is now quite outdated.
The brain is very active during sleep, and some parts of the brain more so than during wakefulness.
Experimental and large population studies have highlighted that sleep is crucial for good health and optimal functioning.
Some processes are unique to sleep and cannot happen at any other time.
For example, connections between neurons are strengthened during sleep.
We consolidate memories and optimise our capacity for learning during sleep, and our brain is flushed of harmful proteins that can lead to long-term damage.
Myth 8 - Drinking alcohol in the evening will help you sleep
Alcohol certainly helps us get off to sleep easily but is ultimately harmful to our sleep.
Any of us who have overindulged in alcohol will recall sleeping like a log in the first portion of the night, but then experiencing a fitful night of frequent awakenings, racing heartbeats, stomach upsets and, potentially, bad dreams.
Alcohol changes the structure of our sleep, such that we have very little REM (rapid eye movement) sleep while we are processing alcohol.
The downside to this is that we experience a "REM withdrawal" and once we have processed all alcohol, our sleep is predominantly made up of REM sleep.
REM sleep is a sleep stage associated with variable sympathetic nervous system activity, which leads to broken sleep, as well as frequent changes in the body's processes such as heart rate and breathing.
There's a simple rule when it comes to alcohol; the more we put in our body and the closer to bedtime we consume, the more it affects our sleep.
Myth 9 - The early bird gets the worm
Aside from the obvious metaphor about beating the pack, this might also be interpreted as giving you more opportunity to get things done and, therefore, succeed.
However, in relation to sleep, this would only be true if the early bird also got enough sleep the previous night and the early bird is truly a natural early bird.
It is important to note that cutting your sleep short by waking early does not give you an advantage.
Natural early birds consistently go to bed and wake earlier, rather than setting the alarm to wake early, than the average person.
However, there is no evidence that those who wake earlier function better than those who wake at more usual times.
How can you work out your natural sleep need and timing?
Choose a two-week holiday period, and sleep in an ideal environment without any alarms.
You'll likely catch up on sleep in the first week.
Your sleep habits in the second week are likely your natural sleep habits.
Myth 10 - Using smartphones and tablets before bed has no effect on your sleep
Using devices with bright light emitting screens before bed can make it hard to fall asleep when you want to and affect the quality of your sleep.
Light in our external environment provides information for our circadian body clock about what time of day it is.
Bright light reminds our body clock that it is daytime, which logically does not promote sleep.
Unfortunately, the electronic devices that we are so fond of emit bright light that contains a significant proportion of blue wavelength light.
Blue light happens to have a much stronger influence over our body clock and studies investigating the impact of blue light have shown that it has a profound effect on the timing of our sleep.
Studies have shown that using bright light emitting e-readers for just 30 minutes in the two hours before bed can shift bed times approximately one hour later.
Having a smartphone in the bedroom overnight can lead to additional disruption.
Notifications from smartphones can wake you up and the bright light that we expose ourselves to while checking text messages and emails in the wee hours of the morning may lead to difficulty falling back to sleep and changes in our sleep structure.
Sweet dreams - Dr Karyn O'Keeffe shares 10 tips to improve your sleep
1 Aim for seven to nine hours of sleep each night to function at your best and stay well.
2 A regular bed and wake time - even on weekends - can be extremely helpful for promoting good quality sleep and helping you get off to sleep when you want to.
3 If you must nap during the day, keep them short and sweet so you don't affect your night time sleep or leave yourself groggy when you wake. You should aim for 20 to 40 minutes from the time you put your head down.
4 Keep alcohol and caffeine intake to a moderate level. Avoid consuming alcohol in the two to three hours and caffeine in the five to eight hours before bed.
5 Going to bed hungry may lead you to wake often during the night. A light snack before bed can be helpful. An overly full stomach at bedtime may lead to discomfort and awakenings overnight.
6 Regular exercise is a great way to improve the quality of your sleep and helps establish a regular sleep routine. Exercising in the late afternoon or early evening is best. Try to avoid intense exercise in the two to three hours before bed.
7 Light shines through our eyelids while we sleep and can lead to poor quality sleep. Block out as much light as you can with good quality curtains, and make sure all your lamps are turned off at bedtime.
8 It's amazing the damage a little noise can do to your sleep. Make sure your radios, TVs, computer, tablets and mobile phones are turned off before bed.
9 We get off to sleep easiest and get the best quality sleep when the bedroom is reserved for sleep and sex.
Avoid bringing work and recreational activities into bed with you.
10 Being exposed to bright light just before bedtime can make it hard to get off to sleep when you want to.
Dim the screens on your tablets, computers and mobile phones in the evening. Ideally, try not to use them in the two hours before you go to bed.
Dr Karyn O'Keeffe, PhD, is a Research Fellow at the Sleep/Wake Research Centre, Massey University. She began her career as a clinical sleep physiologist and transitioned in research and lecturing on sleep and circadian science. Her research interests include managing fatigue in healthcare professionals, treatment provision for sleep disorders, and improving sleep health for the general population.
How we learn in our sleep
Ever dream about important things you learned during the day?
There's a straightforward reason for it: scientists have shown how our brains "back up" memories during sleep, just like a computer hard drive does with data.
This is thanks to the hippocampus, a brain structure that sits symmetrically in both sides of the brain.
Each hippocampus is about 7cm long in an adult human and looks a little like a giant cashew nut.
It is the brain area where memories are initially stored and, as a result, if you damage both your hippocampuses you will lose the ability to store new memories.
Professor David Bilkey, a lecturer and systems neuroscience researcher at the University of Otago, and his research group look at how the hippocampus stores memories, how those memories are communicated to and from other brain areas, and what happens to the hippocampus in disorders such as schizophrenia, where there is memory dysfunction.
An experiment with rats, carried out in the early 2000s by noted MIT neuroscience researcher Professor Matthew Wilson, demonstrated links between non-dreaming sleep and memories of the maze they had run the day before.
It showed that when the animal was in slow-wave sleep, the hippocampus generated small bursts of activity that seemed to be a rapid playback of experiences that it had had during the day.
"It was proposed that this might be the way that the brain transferred new memories from the hippocampus into other parts of the brain for long-term storage," Professor Bilkey said.
"Since that time there has been a lot of work aimed at testing this proposal."
It was known that other parts of the brain were activated in synchrony with the hippocampus when it generates these "playbacks", a finding that supports the idea of memory transfer or "back-up".
Scientists also knew that selective disruption of these playback events during sleep results in poorer memory.
"Exciting recent work indicates that these bursts of hippocampal activity are not just replays of prior experience but that some of them are simulations of what an animal might experience in the future," he said. "This suggests that sleep might function to not only consolidate memory, but also to allow the brain to try out behaviours that might be useful in some future scenario."
Although researchers could not actually see these events happening in the human brain, they knew that the basic structure and functionality was similar across the species.
"There is a lot a recent work showing that sleep in humans, and particularly slow-wave sleep, is very important for strengthening or 'consolidating' memories."
- Jamie Morton
