Science

Sleep science: Part 1 – Why sleep matters, and how to measure it

Rhian Male, MSc

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TABLE OF CONTENTS

Sleep is important. So much so, we spend about a third of our lives doing it. Many of us experience the odd night where we sleep less well, which can affects how we feel the next day. For some, trouble with sleep – like difficulty falling asleep, or waking often during the night – can become a frequent problem.

In part one of this series, we’ll explain why sleep is so important. We’ll delve into why we do it, and the consequences of not getting enough. We’ll describe the science behind what happens when we sleep, and explore ways to measure and track how well we’re sleeping.

In part two, we’ll focus on how sleep patterns differ, common issues some people experience, and set out some tips for optimising sleep.

In part three, we’ll explain how digital interventions can help with sleep, plus the recent efficacy study that evaluated Unmind’s Sleep Tools.

Sleep is important because it has biological and psychological functions

We spend much of our lives sleeping. In fact, sleep isn't just a human thing – almost all animals do it. Though animals vary in the amount they need (depending on things like body size, habitat, predators and food supply), sleep is essential for survival. 

So what happens while we’re sleeping that helps us to survive?

First, sleep has biological effects on our bodies. Some examples are that it helps the body with growth, repair and conserving energy, it reduces levels of inflammation, and it helps remove toxic substances made when the body breaks down food, chemicals, drugs or body tissues. 

For humans in particular, sleep also has important psychological functions. For example, sleep aids processing and forming of memories, learning, and processing and regulating emotions.

Sleep is a major public health issue

Though some people describe themselves as ‘good sleepers’ – falling asleep quickly, and consistently getting enough sleep to feel at their best the next day – sleep is a major public health issue.

A large US study found that 35% of adults don't get enough sleep. This has been a growing problem over recent decades, for various reasons, including:

  • Increasingly long working hours, expectations and balancing different areas of life (like work, family, hobbies, and necessary life admin) that eats away at available sleep time.
  • The negative impacts of mental and physical health problems on sleep, problems which are very common. That said, this is a two-way issue. Sustained insufficient sleep can also increase the risk of developing some physical and mental health problems. Some examples include chronic pain and obesity (as, for example, sleep affects our levels of hormones that suppress or increase our appetite).

So, in conclusion, optimising sleep is really important for maintaining our physical and mental health, and it’s something many of us could gain from working on. 

Sleep and wakefulness are induced by different areas of our brains, and our sleep consists of four different stages

Have you ever wondered what sleep actually is and how it works?

Sleep is a behavioural state, where we’re less active, low in attention to what’s going on around us, and where we may dream. Our brain’s activity is different compared with when we’re awake, and so is our heart rate, blood pressure, body temperature and breathing. 

But how does our body know it’s time to sleep and how do we switch from being awake to being asleep? One theory is that we have two systems that keep track of when it’s time to sleep. 

  • First, we have our circadian rhythm. These are physical, mental and behavioural changes that follow a roughly 24-hour cycle (our ‘biological clock’), which responds to light and dark in our environment. 
  • Second, we have an accumulated need for sleep (a ‘sleep drive’), based on how many hours we’ve been awake for. 

These two systems influence multiple areas in our brains, which in turn work to either induce sleep or wakefulness. For example, when light is absent, one of these centres in the brain (called the pineal gland) produces a hormone named melatonin, which helps induce sleep.

Our sleep happens in four consecutive stages – two stages of light sleep, followed by deep sleep, then REM (or 'rapid eye movement') sleep, where we tend to dream. Each night we go through 4-5 cycles of these four stages. Earlier in the night, the duration of deep sleep is at its longest, while we spend more time in REM sleep later in the night. 

In clinical settings sleep can be measured using questionnaires or in a sleep lab 

Because optimising sleep is important – and many people aren't getting enough sleep – there are many settings where people are keen to measure sleep. There are different ways of doing so, each with their own pros and cons.

First, sleep is measured in clinical settings. This can reveal things like the nature of sleep difficulties someone is experiencing, their severity and how they impact day-to-day life. When measured over time, this can show how well any sleep interventions are working. 

This often involves using sleep questionnaires, like the PROMIS sleep disturbance and sleep-related impairment measures. These ask you to rate various aspects of your sleep on a five-point scale – like how much difficulty you have getting to sleep, and staying awake during the day.

Sleep questionnaires are convenient and cost-effective, and can reveal when someone’s symptoms meet diagnostic criteria for a sleep disorder. They’re also great for use in research. That said, they’re somewhat prone to error as they’re subjective

For diagnosing less common sleep disorders, clinicians may use a method called polysomnography. This involves making objective recordings of factors like someone’s brain waves, eye movements and muscle activity over the course of a night’s sleep, in a lab. But, as you might guess, that’s expensive and resource-intensive. 

You can measure your own sleep using a sleep diary or wearable device

You might be interested in measuring your own sleep – even if you’re not experiencing significant trouble sleeping. There are a couple of ways you can track your sleep patterns over time, and look out for things that affect how well you sleep.

  • One fairly simple, non-costly method is to keep a sleep diary. This means noting down things like what time you went to bed, your activity levels, caffeine intake and any naps taken, plus how much sleep you get each night, and how many times you woke up in the night. 
  • Another currently popular method is using commercially-available wearable devices on your wrist/ankle, with inbuilt sensors which detect movement. These are user-friendly (and fun), but as they’re indirectly measuring sleep they may not be precise. Some devices can also measure environmental factors like light levels and temperature. 

In part two, we’ll take a look at the variations in different people’s sleep patterns and how factors like age and particular stages of life affect our sleep patterns. We’ll also describe some of the difficulties people can have with sleep, as well as setting out some tips for optimising sleep. 

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