We spend a third of our lives fast asleep, yet scientists are only now beginning to understand the phenomenon that has us yawning and stretching once at least every 24 hours.

While processes like eating, drinking and mating have been understood thoroughly through science, sleep still remains a bit of a biological mystery that has eluded scientific judgement.

What happens when we don’t sleep?

Do you know that the Guinness Book of Records has banned voluntary sleep deprivation records, because of how dangerous it has proven to be in the past? Getting no sleep leads to the quickest reduction of health(1) and increases risk for cancer, mental health issues, metabolic syndrome and cardiovascular disease.

You might have noticed yourself how your ability to perform cognitive tasks involving learning, memory or concentration nosedives after an all-nighter. Sustained wakefulness for 17 hours leads to a decrease in performance equivalent to a blood alcohol level of 0.05%, akin to having consumed two glasses of wine.

Insufficient or poor-quality sleep impacts oxidative stress(2) which leads to a domino effect of occurrences that lead to neuronal death; one of the parts in the body that is extremely sensitive to neurons is the hippocampus in the brain, responsible for learning, emotions and memories.

Recent research(3) by the Rochester University team has found that the brain has a “sewage system” (called the glymphatic system) that kicks in during deep sleep; glial cells shrink in size by up to 200% to allow cerebral spinal fluid to flow in and wash out the “metabolic detritus” of wakefulness.

This “sewage system” never kicks into place when deep sleep isn’t achieved, and research has shown that a lack of sleep may be linked to risk factors for obesity and Alzheimer’s disease, as well

How much sleep is required?

There is no definite number of hours that works for everybody across age groups, but on an average, most adults need seven to nine hours of sleep to be well-rested and productive the next day. Toddlers and babies tend to sleep more, which may boost growth and development, while the elderly generally experience lighter sleep once they’re in their 60’s, and often deal with sleep interruptions

Sleep disorders are rampant today, with 50 to 70 million Americans reporting having one(4). Insomnia is the most common sleep disorder, with short-term issues reported by about 30% of adults and chronic insomnia by 10%, while others face sleep problems due to anxiety. Sleep apnea is another common sleep disorder which affects more than 18 million American adults.

Jim Horne from Loughborough University’s Sleep Research Centre puts it simply, “The amount of sleep we require is what we need not to be sleepy in the daytime.”

What are the different stages of sleep?

There are basically two types of sleep: rapid eye movement or REM sleep and non-REM sleep, which constitutes of three different stages. This is the sleep cycle you go through every night:

Non-REM Sleep

Stage 1 of non-REM sleep constitutes the transition from wakefulness to sleep. There’s light sleep, a slowing down of your heartbeat, breathing and eye movements and slight muscle twitching. 

Stage 2 of non-REM sleep is marked by a period of light sleep preceding deeper sleep. Your muscles relax further, your eye movements stop and body temperature drops. 

Stage 3 of non-REM sleep constitutes the deep sleep that leaves you feeling well-rested the next day. Occurring during the first half of the night, your heartbeat and breathing are at their lowest levels during this stage of sleep, and it may be difficult to wake you up. 

REM Sleep

REM sleep first occurs about 90 minutes after falling asleep.  Your eye movements are rapid, with your eyes darting from side to side behind closed eyelids. Most dreaming takes place during this stage, although some can also take place in non-REM sleep. Your arm and leg muscles are practically paralysed, so you don’t act out your dreams, and your breathing becomes faster and slightly irregular, with your heart rate and blood pressure increasing to almost the levels they work at when you are awake. In the second half of the night, the majority of the sleep we get is REM sleep.

What are the biological mechanisms involved in sleep?

There are two internal biological mechanisms at work that regulate sleeping and wakefulness – circadian rhythm and homeostasis. 

Circadian rhythms – Most living beings have an internal timing device or a biological clock that is based approximately on a 24-hour cycle. Your circadian rhythm responds to environmental cues such as light and temperature, and that’s how it controls your biological clock and tends to cause you to wake up in the morning and fall asleep at night. 

Sleep-wake homeostasis controls the drive for sleep by reminding the body of the need for sleep after a certain amount of time; it also regulates sleep intensity. This mechanism too responds to exposure to light, and is influenced by other factors such as medications, jet lag, stress and diet. 

What are the four pillars of sleep?

Matthew Walker, professor of neuroscience at UC Berkeley and expert on sleep, has concisely spelt out the four pillars of sleep in his podcast with Peter Attia:

  • Regularity (or consistent sleeping and waking timings)
  • Continuity (or number of sleep interruptions per night)
  • Quantity (in total, and in each stage of sleep)
  • Quality (stimulants such as caffeine or alcohol can have an effect on quality of sleep)

Simply put-

Sleep is essential for survival – especially quality sleep at the right time. It is a complex process that is important to brain functions(5) and affects almost every type of tissue and process in the body – from metabolism to the immune function(6). 

Most people find it difficult to respond quickly in rapidly-changing situations or focus when they’re sleep-deprived, as sleep helps you create or form pathways in the brain that allow you to learn or create memories. 

For a deep dive into the various sleep stages, sleep cycles and the corresponding brainwaves, listen to this podcast by Peter Attia, MD,  in conversation with Matthew Walker, Ph.D. on sleep. We look at several other issues related to sleep in our other articles in the series, including common sleep disorders and their possible causes , an enquiry into whether sleep deprivation escalates the risk of certain diseases and whether technology can provide us with some sleep solutions.