All your sleep-related questions answered
Hands up if you get eight hours sleep in one solid chunk through the night? If you do, you're probably not a politician, a shift worker or a new parent, all of whom might be getting by on less sleep, daytime sleeps or broken sleep.
So if your sleep is not 'normal', should you be worried? We put some questions to Dr Leigh Signal, senior research fellow at Massey University's Sleep/Wake Research Centre.
Q: Do some of us need less sleep than others?
A: Most of us still need eight hours sleep a night. But some people appear to be naturally short sleepers. There are also a group of people who seem to cope better than the rest of us when they go without sleep. Certain genes have been linked to this ability to cope with sleep loss.
Q: Some researchers are saying seven hours sleep is the new eight?
A: While sleep is an emerging field of research, most of the science suggests that seven hours sleep each night is not enough to sustain your performance over seven days.
The 'health effects' of sleep are a bit different again. When we do large population studies, we see adverse effects on health when people sleep either more than eight hours or less than seven.
Q: Why do some of us wake up at 3am every night?
A: Most of us wake up once or twice an hour - we just don't remember it. It's incredibly normal to wake up at 3am - we've just developed this idea that it's not okay.
Historically, humans would sleep when it got dark and wake up a few hours later, do what we needed to do, then go back to sleep for a couple more hours. Now we think we need one solid block of sleep, so we're making our bodies do something they're not designed to.
If you do wake up at 3am, don't stress about it - it's natural. But try to make up for the loss of sleep by having a nap in the afternoon if possible.
Q: How much sleep do you need to miss in order to be functionally impaired?
A: Reducing sleep by just two hours a night can affect how someone functions and feels the next day. We can see effects in responding to everyday tasks and maintaining attention.
For example, one New Zealand study showed profound effects on driving, with the outtake being if you're feeling sleepy then you are not safe to drive. The more hours' sleep you lose a night, the more striking the effects will be.
Q: Which part of your health is most affected by lack of sleep?
A: When healthy young people are deprived of sleep, we very quickly see changes in immunity.
One study involved restricting young men's sleep to four hours a night, over four nights, before giving them the flu vaccine. They then had two more nights of sleep restriction before their response to the flu vaccine was tested.
It was found that they produced half the antibodies to the vaccine compared to people who were not sleep-deprived. We also see changes in the body's ability to metabolise glucose and appetite hormones - less sleep makes you hungrier. Sleep doesn't affect just one aspect of your functionality - healthwise it goes right across the board.
Q: Is there a problem with getting too much sleep?
A: People who sleep more than eight to nine hours have been shown to have poorer health outcomes. But at present we don't know why this is.
It might be that they have an illness that causes them to sleep for longer periods in the first place. So it's hard to tell whether an existing medical condition, or excess sleep, contributes to the outcomes.
Q: Is it the quantity or the quality of sleep that counts?
A: Both matter. If you don't get the normal cycles of NREM (Non Rapid Eye Movement) and REM (Rapid Eye Movement) you'll feel worse the next day - moodier, irritable, not good at making decisions and slower in responding.
NREM is when brain activity slows down; REM is the vivid dreaming stage of sleep when the brain is busy like it is when you are awake. The whole cycle of NREM and REM takes around 90 minutes and you repeat that cycle through the night. It's important to get enough of both NREM and REM sleep. If you're woken from NREM early in the night, it might feel like you haven't slept at all.
Q: Are there true night owls who really hit their straps late at night? And is it a problem that they sleep by day?
A: A small proportion of the population is very evening-orientated, and they find it impossible to go to bed earlier. Their internal biological clock (circadian clock) is hardwired like that.
We all become slightly more evening-orientated in our teenage years, and then more morning-orientated in our older years. So across the course of our lives, our circadian clock can change.
If you're a true night owl or a morning type, it will be very difficult to go against your natural rhythms - don't force yourself to sleep when you can't.
But do note, we are designed to sleep by darkness - at night - and it's important to get a good quality sleep.
Regardless of the time of night you go to sleep, "don't be duped into thinking you can get away with less sleep," says Signal.. What's important is prioritising sleep - making time for it in your day and planning around it.
Sleep is not a nice-to-have - it's essential to daily functioning.
And getting a pre-sleep routine in place is also important. The bedroom is no place for bright light or the blue light that comes from tablets and phones, she says. If you care about a good night's sleep, keep the gadgets out of sight and blissfully out of mind.
Happy sleep to you, Stuff readers.