What is sleep? The science of sleep﻿: Part 2

Image of the moon in a black sky

We spend around a third of our lives asleep, but why? In the past, people have thought that sleep was simply a hindrance, a wasted time of day when you couldn’t get anything done. More recently, scientists have started to understand what actually happens to our brain and body when we sleep and why getting a good night’s sleep is so vital.

In Part 1 of this blog post we looked at the different stages of sleep and how these sleep stages repeatedly cycle around every 90 minutes throughout the night. We looked at the importance of REM (Rapid Eye Movement) and NREM (non-REM) sleep, how sleep changes as we age and how our bed and bedroom affect how we sleep.

In this second part, we will look at the drivers for sleep, how caffeine affects sleep and how you can help yourself to get a better night’s sleep.

Drives for sleep

There are two main factors that control when we sleep: our circadian rhythm and our homeostatic sleep drive.

Our circadian rhythm

Our circadian rhythm is our own internal 24 hour clock. This is the clock inside us which tells our bodies when it is time to sleep, when it is time to wake, when it is time to eat, when to be alert and or drowsy and regulates our hormones and temperature. Our body temperature increases during the daytime and falls at night. Most people don’t even notice their own circadian rhythm until they go abroad on holiday to a different time zone, when it goes wrong… For example, if your body is used to being on “UK time” but you are now in America, then your circadian rhythm will tell you that its time for bed and make you very sleepy, when the local clocks tell you it it is the afternoon and time to explore the city!

Image of New York City through a single lens of a pair of glasses.

Our circadian rhythm is mainly regulated by sunlight. Just like flowers that know when to open their petals to the sunshine, our bodies use the sun to know when it is daytime. This means that you can boost your circadian rhythm by making sure that you get outside to get some natural sunlight, ideally in the morning. This is a great way to fight jetlag. However, some electronic devices can interfere with this process. Devices such as phones and tablets produce “blue light” which is the same frequency light as our brain uses to identify day and night, so when we use them in the evening we are telling our brains that it is the middle of the day – and that we should not be going to sleep anytime soon. In fact, our circadian rhythms make us naturally produce a hormone called melatonin in the evening to tell our bodies to start going to sleep, but the blue light from tablets and phones suppresses this natural production of melatonin – stopping us being able to go to sleep easily.

“Blue light” from tablets and phones suppres our natural production of melatonin – stopping us from being able to go to sleep easily. Switch off devices at bedtime.

The homeostatic sleep drive

The longer we are awake, the greater our “drive” for sleep. This is known as our homeostatic sleep drive. If we have been awake for a very long time (such as staying up very late into the early hours or the morning) then this drive for sleep will keep increasing. In contrast, when we take a nap we reduce our homeostatic sleep drive. This means that an afternoon nap will make you feel refreshed, but also reduce your drive for sleep that night – that is why you might struggle to fall asleep in the evening if you took a nap during the day.

Naps are great, but remember that they count towards your total sleep time for the day.

How does caffeine affect sleep? 

Caffeine stops our brains from being able to recognise our homeostatic sleep drive. Even if we are very tired, as we have not slept for a long time, when we drink caffeinated drinks or eat chocolate, the caffeine stops our brains from being able to tell that we actually need sleep. Most importantly, caffeine has a 5-7 hour half life, meaning that 5-7 hours after a cup of coffee, half of the caffeine will still be in your system. It is best to limit caffeine to the morning, to give you the best chance of getting to sleep at night.

Spring cleaning your brain

During sleep your brain gets flushed with cerebrospinal fluid to “spring clean” it. It is suggested that when we do not sleep enough our brains clog up with waste products that have not been removed (including amyloid plaques) which could be linked to diseases such as Alzheimers. 

Your bedroom temperature

In the last article we looked at how your bedroom should be a place of relaxation and a haven for promoting sleep and that your bed should be supporting your back properly to keep you comfortable and asleep during the night. Further, as we fall asleep our body temperature naturally drops. Therefore, if our bedroom is too hot, then your body temperature will struggle to drop which will hinder sleep. Make sure that your bedroom is cool enough and that your bed does not make you too hot. Consider sleeping with a window open, or making sure that your mattress and covers allow air to circulate instead of making you too hot and sweaty.

In this two part blog we have explored what sleep is and the science behind how you can make real changes to help you sleep better. We hope that you have learned something and wish you a peaceful night’s sleep.


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