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The Need for Sleep
We know that sleep is important for the regular functioning of our bodies. But to our ancestors, sleep made them vulnerable to attacks from wild animals and predators. So this begs the question, why do we sleep?
25 August, 2021

For many years scientists have been researching a phenomenon that we still cannot fully understand – sleep. We know that sleep is important for the regular functioning of our bodies. But to our ancestors, sleep made them vulnerable to attacks from wild animals and predators. So this begs the question, why do we sleep?

Our brain controls our thoughts, memory and speech, movement, and the function of many organs in our body. During the day, our brain is working to keep our body functioning properly while also creating memories for all the experiences we encounter. At night while sleeping, the brain strengthens these memories so that mammals (mainly humans) don’t forget them. Recent studies however suggest that during sleep, the brain also prepares itself for the next time humans wake. It thus acts like a dry sponge ready to soak up new information that cannot absorb new memories if it gets waterlogged.

To understand why sleep is important we need to understand what sleep is. Sleep is the natural and reversible periodic state of many living things that is marked by the absence of wakefulness and the loss of consciousness. In simple terms, it’s a state of torpid inactivity. There are 4 stages of the sleep cycle. Awake time is a natural break in sleep, light sleep guides you into deeper stages, deep sleep focuses on restoring your body and REM (rapid eye movement) sleep re-energizes your mind. 

Stage 0 of the sleep cycle is the awake time phase. This is the time spent in bed before and right after falling asleep. It also includes brief awakenings during sleep. Stages 1 and 2 are known as light sleep, wherein muscles relax, respiration slows, heart rate decreases and body temperature drops. At this stage, sleep begins or transitions between cycles and waking up is easier. The next stages 3 and 4 are known as deep sleep, where blood pressure drops and the body promotes muscle growth and repair. The blood flow to muscles is increased, growth hormone is released and tissue growth and cell repair occur. Studies have shown that in this stage the brain flushes waste and shows long, slow brain waves. Waking up is more difficult and you are disoriented if awoken. The last stage is (REM) sleep. During REM sleep our brain is almost as active as when we are awake. Respiration and heart rate increases, temperature regulation is switched off and vivid dreams occur. The body becomes immobile to stop you from acting out your dreams. This cycle is beneficial for memory, learning and problem-solving. 

On average one sleep cycle lasts 90 minutes and typically every time you sleep your body goes through four to five sleep cycles. Data shows that overall, your body spends the majority of the night in light sleep i.e. about 45-55%  of the sleep cycle. The amount of time you spend in REM of the deep cycle can vary between individuals but on average deep sleep is 13-23% of your sleep cycle and REM sleep is 20-25%.

Sleep disruption or lack of sleep can have short-term and long-term consequences. Short term consequences can cause irritability, decreased creativity, increased stress, decreased accuracy, tremors, and memory losses. Long term consequences can instead include hypertension, dyslipidemia (abnormal amount of lipids), cardiovascular disease, weight-related issues, type 2 diabetes, and colorectal cancer. 

Throughout your life, you may have been told different recommended hours to sleep depending on how old you were. Different age groups require different amounts of sleep and sleep at different times.

Babies and toddlers tend to sleep most of the time, around 11 – 17 hours a day. This is mainly to let their body grow and develop. During adolescence, the body’s circadian rhythm is reset, resulting in teens and young adults typically staying and waking up later. The recommended hours of sleep for this population group is 8 – 10 hours. Younger adults are recommended to get 7 – 9 hours a night whereas older adults are recommended 7 – 8 hours as per the National Sleep Foundation.

Sleep is thus an essential function that allows your body and mind to recharge.

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