We spend around one-third of our lives asleep. Though, up until 30 years ago or so, scientists knew fairly little about what really happens when our heads hit the pillow.
But thanks to research, we now have a much deeper understanding of sleep, and with that comes a variety of fascinating facts.
With this in mind, we’ve put together 20 interesting facts about sleep; covering what it looks like for us, as well as in the animal world. We hope you enjoy them!
1. Some people dream in black and white, while others dream in colour
Some research has found that older adults tend to dream in black and white, while younger people dream in colour.
This study looked at the dreams of two age groups (25 and younger, and 55 and above). It found that many of the participants over 55 had black-and-white dreams, while the younger age group dreamed in colour – never or rarely experiencing black-and-white dreams.
Researchers have linked these differences to the impact that television has had on our sleep experiences. For example, dreaming in black and white is largely linked to childhood exposure to black-and-white television, and vice versa.
Our article, 10 fascinating facts about dreams, has more information and interesting facts.
2. Falling asleep should ideally take 10 to 20 minutes
3. 4% of UK adults sleepwalk
While sleepwalking is most common in children, plenty of adults do it too. Studies show that around one in five UK adults sleepwalk, which is equal to over 10 million people.
Like other sleep disorders, sleepwalking tends to run in families and it’s thought that having a parent or sibling who sleepwalks makes you 10 times more likely to sleepwalk yourself.
Environmental factors – such as stress or lack of sleep – can also play a role, as well as conditions like fever, acid reflux, nighttime asthma, and sleep apnea.
4. Dolphins and whales only fall half asleep
Scientific research has found that marine mammals like dolphins and whales only ever fall half asleep. Each side of their brain takes turns to rest to allow them to come up for air.
While half asleep, marine mammals may be less responsive, but amazingly, will keep swimming and can still monitor their environment to a certain extent.
5. It’s impossible to sneeze during REM sleep
Throughout the night, our body goes through different stages of sleep. REM (rapid eye movement) sleep is the stage where dreams usually occur.
To prevent us from acting out our dreams, our muscles enter paralysis as a safety mechanism. As a result of our muscles not actively functioning, it becomes impossible to sneeze during this stage of sleep, and only our breathing and eye muscles are left operating.
Other urges that are generally suppressed during sleep include hunger, thirst, and hiccups.
6. Sleep deprivation is similar to being drunk
According to studies, the effects on our reaction time, vigilance, multitasking, and hand-eye coordination after 18 hours of being awake are similar to having a blood-alcohol level of 0.05%, and 0.08% after 20 hours. In the UK, the blood-alcohol limit is 0.08%.
As a result, sleep deprivation can be as dangerous as drink driving.
7. Noise can wake us up, but smells can’t
Research has revealed that noise can wake us up from sleep, but smells can’t. For example, in this study, neither the smell of peppermint nor noxious pyridine (a component of coal tar) woke participants up.
This is one of the reasons why fire alarms were invented.
8. Women may need more sleep than men
According to research, women need around 11 minutes more sleep than men because their brains are more active and need more time to recover.
Sleep is the time for our brains to go into repair mode and, as stated by neuroscientist Jim Horne, women “do lots at once, are flexible, and use more of their actual brain than men do.”
9. Tigers and human babies need the same amount of sleep
Research has shown that human babies and toddlers need around 16 hours of sleep a day for body and brain development. This is the same amount of sleep as a fully grown tiger, which needs to conserve energy and rejuvenate to stalk, sprint, and kill.
While this may seem like a lot, some animals sleep even more. The koala is recognised as the sleepiest animal in the world – spending between 18 and 22 hours a day asleep.
10. Different nap lengths offer different benefits
On the whole, naps have been shown to reduce drowsiness and boost alertness. However, research has found that different nap lengths offer different benefits in terms of mood, alertness, and performance.
For example, studies have shown that micro naps (as short as six minutes) can improve memory and napping for 10-20 minutes can help to boost confidence and alertness.
Meanwhile, creative thinking and emotional processing skills rely on REM sleep, which typically appears in naps lasting at least 60 minutes.
11. We forget 90% of our dreams 10 minutes after waking up
Studies of brain activity have revealed that people aged 10 and over dream between four and six times per night.
However, five minutes after waking from a dream, it’s estimated that we forget 50% of its content – increasing to 90% five minutes later. Though, some people rarely remember dreaming at all.
12. Sleeping immediately after learning something may improve your ability to remember it
Sleeping helps to boost our memory, and REM sleep in particular is one of the most crucial stages of sleep for consolidating memories. As a result, research has shown that sleeping immediately after learning something may improve your ability to remember it.
For example, in this study participants were randomly asked to study unrelated word pairs at 9am or 9pm before returning to be tested on their memory 12 hours later. It found that the participants’ memories were superior after the 9pm study, which was followed by a good night’s sleep, as opposed to a day’s wakefulness.
13. Sea otters hold hands while they sleep
To prevent themselves from floating away from one another, sea otters hold hands while they sleep.
14. Afternoon slumps are a real thing
There’s a scientific explanation behind why many of us start to feel a bit sleepy between 2-3pm.
Research shows that most people experience higher levels of the stress hormone cortisol in the morning and blood pressure typically peaks around midday, before starting to drop in the afternoon and evening. This, paired with post-lunch blood sugar fluctuations can leave a lot of us experiencing an afternoon slump.
On the other hand, peak alertness sets in around 2-3 hours and 8-9 hours after we first wake up.
Why not check out our article 18 tips to avoid an afternoon slump to learn more?
15. Lack of sleep can cause overeating
Getting a good night’s sleep promotes the healthy production of hormones like leptin and ghrelin, which are needed to regulate our appetite.
A lack of sleep can lead to an imbalance of these hormones and leave us feeling more peckish during the day.
For example, this study found that people who are sleep-deprived eat an average of 385 extra calories per day. In line with these findings, other studies have drawn a significant link between a lack of sleep and obesity.
16. Social jet lag is a real thing
Social jet lag is defined as staying up later and sleeping in later on the weekends than you do during the week, as a result of your social calendar.
Changing the hours that you sleep day-to-day affects your circadian rhythm and can leave your body feeling like it’s in a different time zone.
As a result, studies have revealed that social jet lag affects the body in a similar way to travel jet lag, which, for many people, will explain why they often feel tired returning to work on a Monday morning.
17. Somniphobia is the fear of sleep
Somniphobia is a phobia where people fear sleep.
People with somniphobia may obsessively worry throughout the day about having to go to sleep; for example, due to fear of having nightmares or sleepwalking.
While somniphobia and sleep anxiety both involve feeling anxious, the two conditions differ. While people with sleep anxiety may worry about getting enough sleep, those with somniphobia often experience a more intense fear that something bad will happen to them when they fall asleep.
18. Humans are the only mammals that willingly delay sleep
All other mammals realise how important sleep is for their health and, wherever possible, won’t allow it to be compromised.
Humans, on the other hand, whether due to social plans, technology, or other commitments and pastimes, often put sleep off.
19. New parents miss out on the equivalent of 50 nights of sleep in their baby’s first year
Studies have found that new parents get an average of 4 hours and 44 minutes of sleep per night in the first year of their baby’s life. This is 59% less than the recommended eight hours per night.
Over the course of one year, this is equivalent to losing 50 nights of sleep.
20. Elephants sleep less than any other mammal
The popular phrase “an elephant never forgets” really doesn’t line up with science at all.
The REM stage of sleep is where memories are processed. And while humans spend around 20-25% of their time asleep in REM per night (around 90 minutes for 7-8 hours of sleep), research has found that elephants only go into REM sleep every three to four days – and even then, only sleep for around two or three hours at a time.
Final thoughts…
Sleep is essential for our health and it can be interesting to build a better understanding of what goes on once we close our eyes.
For more sleep-related content, head over to the sleep and fatigue section of our website. Here, you’ll find everything from tips to beat insomnia to how to find the right pillow and mattress for you.
What are your favourite facts about sleep? Do you have any other facts that you’d like to share? We’d love to hear from you in the comments below!