Hunter-gatherers seemed to get away with around six hours of sleep a night, but how do modern humans fare with that much shut-eye?
We’ve all wondered whether we’re getting enough sleep. You wake up feeling sluggish and try to shuffle to the kettle before somebody engages you in conversation. Eight hours of sleep a night may be a luxury you can’t afford. But is six hours really that bad?
While hunter-gatherers may have only averaged just 6.4 hours of sleep a night, experts say that this simply doesn’t cut it for most modern humans.
The US National Sleep Foundation recommends adults have 7-9 hours of sleep each night. They have a good reason for saying this, but it’s not a rule that will apply to everyone.
Recommended sleep hours
The recommended amount of sleep is, as per the Sleep Foundation…
| Age range | Recommended hours of sleep |
|---|---|
| 4-12 months | 12-16 hours (including naps) |
| 1-2 years | 11-14 hours (including naps) |
| 3-5 years | 10-13 hours (including naps) |
| 6-12 years | 9-12 hours |
| 13-18 years | 8-10 hours |
| 18 years and older | 7 hours or more |
Does everyone need the same amount of sleep?
No, not every person will need the same amount of sleep each night.
“Not only do some people need more sleep than others, but sleep requirements change throughout the life course,” Alice Gregory, a professor of psychology at Goldsmiths, University of London and author of Nodding Off, explains to BBC Science Focus.
“For example, a toddler will need roughly 11-14 hours of sleep, whereas older adults need around 7-8 hours per night. It is also the case that sleep requirements can vary under certain circumstances – during periods of illness, for example.”
Read more:
- What does sleep do for the brain?
- How hidden ‘overtiredness’ is ruining your sleep – and how to fix it
- Can’t stop your brain racing at 3am? Try these suggestions from a GP
Can I get by with six hours of sleep?
Whether you can get by on less than the National Sleep Foundation recommendations for your age group – and none of them drop as low as six hours – comes down to the body you’re born into.
“For some individuals, obtaining six hours of sleep per night may be enough,” Gregory says.
“In addition to the sleep length recommendations, the National Sleep Foundation emphasises individual differences and notes that slightly less or more sleep than the published recommendations may be appropriate for some people.”
There are some short sleepers who have been dealt a good genetic hand and can do perfectly well on around six hours of sleep. But the emphasis here is on ‘some’. And if we’re talking less than six hours, then the likelihood of it being healthy drops considerably.
Matthew Walker, a professor of neuroscience at the University of California, Berkeley, talked about people getting less than six hours on the BBC Science Focus Instant Genius podcast in 2021, and it’s not good news.
“We know that the number of people who can survive on less than six hours of sleep and show no impairment in either the brain or the body, rounded to a whole number and expressed as a per cent of the population, is actually zero,” Walker said.
How much sleep do I need?
Sleep researchers have been trying to figure out how much sleep we need, which is where the National Sleep Foundation recommendations come from. Gregory said that’s the place to start if you’re concerned.
“If you think you are not getting an appropriate amount of sleep, you might want to gradually adjust your sleep length,” Gregory said.
“You may want to slowly increase the amount of sleep you get if you struggle to wake up in the morning, need lots of caffeine to get going or are sleepy and performing poorly during the day.”
In short, if you feel like you haven’t got enough sleep and you wake up feeling lethargic, you’re shut-eye has likely been too short. However, if you’re able to wake up without an alarm, and in a reasonably good mood – and not craving caffeine – you’re likely getting enough.
While it may seem obvious when we haven’t slept enough, it’s worth also noting that our brains can overestimate our ability to function on less than sufficient sleep.
On the Instant Genius podcast, Walker said: “Your subjective sense of how well you’re doing when you are not getting enough sleep is a miserable predictor of objectively how you’re doing when you’re not getting sufficient sleep.”
Walker uses the analogy of a drunk diver who’s had a few drinks at a bar and thinks they’re fine to drive home. Objectively, they aren’t.
“That’s the problem with sleep deprivation as well, we don’t know that we are insufficiently slept when we are not getting sufficient sleep,” Walker adds
Can you die if you don’t get enough sleep?
Not getting enough sleep is associated with a range of health issues, from high blood pressure to heart attacks. While prolonged sleep deprivation is known to be fatal, even losing an hour from our sleep cycle can potentially have a big impact.
A 2014 study published in the journal Open Heart found a 24 per cent increase in the number of heart attacks on the day after we lose an hour of sleep in the spring due to Daylight Saving Time.
The researchers couldn’t say for sure why Daylight Saving Time may be increasing heart attack risk, but the day after the time changes is a Monday, and the hour loss may have compounded other factors such as the stress of going back to work and a change in our sleep cycle at the beginning of the week.
About our expert
Alice Gregory is a professor of psychology at Goldsmiths, University of London and author of several sleep books, including Nodding Off (Bloombury, 2018), The Gift of Sleep: 50 Tips for a Good Night’s Rest (Laurence King Publishing, 2023) and The Sleepy Pebble and Other Stories (Flying Eye Books, 2019).
Read more:
- Why do I always find things to do late at night?
- Getting a good night’s sleep may help to protect you from heart disease and stroke