July 13, 2024

I, Science

The science magazine of Imperial College

Sleep is vital for our bodies to function. Yet as our lives become more hectic, many of us dip in to sleep time for those extra hours. But Ravi Shankar explores why this may not be such a good idea.

Woman asleep on laptop

If you’re reading this late at night on your smartphone – stop. Please switch off your phone and get some sleep. The vast majority of us, who struggle to find some shuteye at night, inevitably find solace by perusing our iPhone or Android devices, either for work or leisure. It’s become a common occurrence in our hectic modern-day lifestyles. Needless to say social media has played an instrumental role in this too. But what effect is this having on us, mentally, emotionally, and physically?

Recently, it has come to my attention that the modern day grind, regardless of whether we are studying or working, rides roughshod over a critical aspect of our wellbeing: sleep. One morning, quite recently, I was waiting for my connecting train to go to work. I came across a gentleman asleep on the platform bench with a cup of espresso in one hand and in the midst of replying to his emails on his phone in the other. Out of courtesy, I gently woke him and inquired if the approaching train (which was incidentally mine) was also his. He nodded and frantically gathered his things. “We have a crucial board meeting this morning and I’ve hardly slept over the past few days.” We very seldom neglect our eating or drinking habits, knowing very well that getting through the day’s work would otherwise be a challenging task. So why does our sleep take a hit like this?


A recent study, conducted by a panel of leading doctors and scientists at the National Sleep Foundation in the US, revealed the recommended hours of sleep depending on our age. For adults aged 20 and above, such as yours truly, 7-8 hours is the minimum recommended sleep duration. In light of this study, the term “sleep debt” was coined by the neuroscience community – let’s do some simple sleep math to illustrate this.

graph showing how few hours people sleep during the work week and how many they sleep on the weekends

For the sake of argument, let’s assume that you had to forgo two hours of sleep every night last week to meet an important deadline on Friday. To compensate, you sleep an additional four hours over the weekend. Come Monday morning, after your kick-start cup of coffee, you may feel bright-eyed and bushy-tailed. But this apparent vim and vigour is short-lived as you are still in sleep debt by six hours – almost an entire night of sleep (see figure above). If the following week is anything like the previous, you may find yourself getting increasingly fatigued, mentally and physically, if this habit ensues.


illustration of human brain

On average, an adult human spends approximately a third of their lifetime (~25 years) sleeping. Yes, a surprising figure isn’t it? Over the past few centuries, rapid advances in modern medicine have helped us to make ground-breaking discoveries in neurology. However, scientists and medical experts are still trying to ascertain exactly what happens in our body when we enter this subconscious state of sleeping. Sleep can be broadly separated into two key stages: non-rapid eye movement (NREM) and rapid eye movement (REM).

A typical sleep cycle has been experimentally measured to last approximately 90 minutes, proceeding in cycles of NREM and REM, with 4-5 cycles per night. Around 75-80% of our sleep cycle falls under the initial NREM category. During this time, the brain emits pulses of electrical signals known as ‘sleep spindles’. It is during this stage that we enter our deepest sleep. Gradually, our brain activity begins to slow down, our breathing, heart rate and temperature drop, and we become progressively more difficult to wake up. Failing to acquire sufficient NREM sleep seriously impairs our judgements and ability to make simple decisions and recollections; this stage is important for transferring short-term memories to long-term storage. Incidentally, it is during this period of deep sleep that we experience peak hormone release for cell repair and regeneration.

This is often why we feel tired and lethargic upon waking up if we kept tossing and turning the previous night. We didn’t recover with deep sleep. After the NREM stage, our brain activity picks up slightly as we subsequently enter the REM stage. The underlying role of REM sleep remains somewhat unclear. However, the consensus is that this is when we experience our most vivid and emotional dreams. Our dreams in the NREM stage typically tend to be more concept-based and pertain to events or actions that occurred prior to sleeping. This cycle is repeated multiple times throughout the night, with our REM stage getting progressively longer each time.


Girl stretching in front of windowBut if this cycle acts on a loop, why do we then naturally wake up after sleep? The answer is simple: our body runs and maintains its own self-operated clock. Aside from environmental stimuli, there are two key processes that regulate our sleeping patterns. Firstly, the circadian process is responsible for managing our governing body clock, which helps us keep to a 24-hour schedule. This clock is in a region of the brain known as the suprachiasmatic nucleus (SCN), which promotes sleep and wake during different part of the day.

Secondly, there is the so-called homeostatic process. Through this process, a range of ‘sleep-promoting’ chemicals (or specifically neurotransmitters) accumulate in our brain when we are awake and when we are asleep, these are gradually removed. Once a critical threshold is reached towards the end of our sleep, the core of our brain is instantaneously flooded with an army of ‘wake-promoting’ neurotransmitters to deliver a message: rise and shine! A good analogy for this process would be flicking a light switch on when a room becomes too dark and vice versa.


In the same way that leaving light on for prolonged periods needlessly consumes power, losing sleep and forcing ourselves to stay awake drains us of valuable energy required to perform our daily tasks. Not only can this lead to impaired productivity and immunity in the short term, but we would be making ourselves more susceptible to serious illnesses, such as diabetes and heart disease. Indeed, it can be difficult at times to get enough sleep. I for one have fallen prey to sleep debt on numerous occasions when trying to meet tough deadlines during my time at Imperial College. But when the opportunity arises to sleep on time, please take it. Work is important, but our health should always take priority. With that, I wish you all, regardless of which corner of the world you are in or what time you’re reading this, a peaceful sleep tonight. Sweet dreams.

Ravi Shankar is studying for a PhD in the Department of Chemical Engineering at Imperial College London

Banner image: sleeping woman, Predrag Sepelj