WHY DO WE SLEEP?
A good night’s rest is an essential part of life, but getting enough can be hard. We take a look at the science behind snoozing and how you can sleep easy
WORDSFRANCES DANIELS
DID YOU KNOW? Your dreams gradually increase in duration as the night progresses, with morning dreams lasting the longest
It takes up a third of our lives and seems to be a non-negotiable part of being human, but what exactly is sleep and why is it essential?
Sleep is often defined as a state of rest, and it does appear that way from the outside.
However, our brains and bodies are working overtime. During sleep, the brain and body go through a schedule of events known as sleep cycles. We typically go through six cycles per night, and each one is made up of four stages. Stage 1 is the period when you first doze off, and it lasts up to seven minutes. Stage 2 lasts for up to 25 minutes and is accompanied by muscle relaxation, a slower heart rate and a cooler body temperature. Next up is Stage 3, commonly known as deep sleep as it’s difficult to wake up during this stage. It lasts up to 40 minutes and is essential for body recovery and growth.
The final stage is rapid eye movement (REM) sleep, because the eyes move quickly even though they’re shut. REM doesn’t occur until you’ve been asleep for at least 90 minutes and lasts up to an hour. Brain activity increases during REM sleep, so you’re more likely to experience vivid dreams in this stage. These sleep stages are vital for both mental and physical health, which is why many sleep experts subscribe to the restorative theory as an explanation for why we sleep. The restorative theory argues that we sleep so the brain and body can prepare for the next day, which is why processes such as muscle growth and tissue repair mostly occur during sleep. Sleep is also needed for memory consolidation, a learning process that turns short-term memories into long-term memories. These are needed to form our understanding of the world, which explains why children and teenagers need more sleep than adults. However, this theory raises a question: if sleep’s sole purpose is to rejuvenate the brain, then why do brainless creatures, such as jellyfish, sleep?
Another theory for why we sleep is the energy conservation theory, which argues that sleep is needed to reduce a person’s demand for energy and food at night. This explanation supports another sleep theory that evolutionary scientists have advocated for – the inactivity theory. This suggests that sleep evolved as a way to save energy for daylight hours, when it’s light and food is more accessible. Evolution favoured our prehistoric ancestors who were active during the day and inactive during the night, meaning they weren’t wandering blindly in complete darkness and vulnerable to nocturnal predators.
Other evolutionary reasons for sleep include the default sleep theory, which argues that sleep is the default state and we actually evolved being awake, and the threat simulation theory, which not only explains why we sleep, but also why we dream. Threat simulation theory suggests that dreams are an evolutionary trait that present us with images of potential threats to prepare us for them in real life. However, the most famous and enduring theory for why we dream was presented by Sigmund Freud, the forefather of dream interpretation. Freud believed that our dreams express our unconscious desires, and we can uncover our deepest thoughts and feelings by decoding them. There is also evidence to suggest that dreaming helps regulate emotions and form memories, but many sleep experts today say that dreams are just a meaningless byproduct of brain activity. The truth is that nobody knows exactly why we dream or sleep, but there’s plenty of science that explains why it’s important…
The most common thing to dream
about is your teeth falling out © AdobeStock / Shutterstock / Alamy
Going without sleep for over 96
hours can cause hallucinations
Nodding off isn’t always easy. Insomnia, a disorder where you struggle to fall or stay asleep, affects a third of people in the UK. Insomnia can happen for a wide range of reasons, depending on the type. Primary insomnia is usually caused by stressful life events, such as money troubles or starting a new job, but secondary insomnia is caused by an underlying health problem. Medical conditions that can cause insomnia include depression, anxiety or sleep apnea, but plenty of other health issues can trigger sleep problems, too. Sometimes medications to help these conditions list insomnia as a side effect, especially antidepressants and medicine for high blood pressure. Insomnia can also be caused by lifestyle habits, such as drinking too much coffee or alcohol, having a sedentary desk job, travelling or an irregular sleep schedule. Even your environment can cause insomnia. Living in a city with high levels of noise or light pollution can affect your sleep, as can a hot or humid home or uncomfortable bed. It’s only when we are deprived of sleep that we see how important it actually is for our livelihoods. Insomnia isn’t just characterised by a lack of sleep, it’s also characterised by mood swings, trouble concentrating and an increased risk of developing health conditions or having an accident.
Did you know?
Jet lag symptoms are worse when flying east
While sleeping is essential to survival, there are plenty of people who’ve tried to cheat slumber. Arguably the most famous case of sleep deprivation is Randy Gardner, a teenager who, back in 1963, decided to see how long he could stay awake for a science fair. He managed to go 11 days and 25 minutes without sleep, but suffered from hallucinations by day four. While Gardner’s experiment broke a world record, his feat was overtaken just two weeks later by another ambitious student who stayed awake for 11 days, 2 hours and 30 minutes. Many more record-breaking stunts followed, with the last record holder going 18 days, 21 hours and 40 minutes without sleep.
DID YOU KNOW? Research has found that a bedtime between 22:00 and 23:00 reduces the risk of developing heart disease
NIGHTMARES VERSUS NIGHT TERRORS
Nightmares and night terrors are two sleep issues that are often used interchangeably, but they couldn’t be more different. A nightmare is an unpleasant or frightening dream that occurs during REM sleep, usually in the early hours of the morning. Both children and adults can have nightmares and they can be triggered by lifestyle factors such as stress, depression or trauma. We sometimes remember our nightmares upon awakening, which can be unsettling, but recurring nightmares can be treated with counselling or meditation.
On the other hand, a night terror is a type of parasomnia (abnormal movement during sleep) that’s similar to sleepwalking. Night terrors occur during deep sleep, so you have no memory of them upon awakening. While it’s possible for adults to experience night terrors, they’re most common in children. There’s no treatment for night terrors, but the good news is that most people grow out of them.
After 1997, Guinness World Records refused to keep monitoring sleep-deprivation records for two reasons: it didn’t want to encourage unhealthy behaviour, and there’s no way to accurately monitor these attempts. Since Gardner’s experiment, researchers discovered ‘microsleeps’, which are defined as lapses into sleep that last mere seconds. It’s likely that Gardener and his successors all lapsed into microsleeps, they just didn’t realise it.
There’s also been a number of experiments throughout history that have explored the effects of sleep deprivation. In 1894, a downright cruel experiment was conducted on ten puppies, who were kept awake for 24 hours a day. By day five, all the puppies had died, and the biochemists concluded that sleep deprivation killed the puppies much quicker than starvation did. Another experiment, conducted in 2015, saw scientists infect healthy participants with a common cold virus. A week later, they found that those who slept fewer than five hours a night were more likely to get sick than those who slept for seven hours or more. The conclusion? Sleep deprivation weakens the body’s natural defence system.
WHAT IS APNEA? Obstructive sleep apnea affects your breathing while asleep. Here’s how it causes insomnia
CAFFEINE CRASH
Our body is full of cells called receptors, which send the brain signals. When a sleep-inducing chemical called adenosine connects to these receptors, it signals to the brain that it’s time to sleep. Caffeine, meanwhile, is a stimulating chemical that looks so similar to adenosine that it tricks the receptors to connect to it instead. When this happens, it causes alertness instead of sleepiness. However, while caffeine takes its spot, adenosine begins to build up. When caffeine eventually wears off, the built-up adenosine reclaims its spot by connecting with the receptors, causing a sudden feeling of tiredness known as a ‘caffeine crash’.
In general, 1 out of 20 people has nightmares every week
© Alamy / Getty
1 OBSTRUCTION When muscles in the throat relax too much during sleep, they collapse and block the upper airway.
2 LESS OXYGEN The obstructed airway means less oxygen reaches the lungs and brain, causing breathing to repeatedly stop and start.
3 BRAIN REACTION The brain reacts to the lack of oxygen through frequent awakenings throughout the night, causing coughing or gasps for air.
4 SNORING A common symptom of sleep apnea is snoring, as the blocked airway causes throat tissues to vibrate against each other.