Understanding the connection between sleep and health
We’re now broadening our research to look at other health conditions, using our unique data-driven approach to tackle some of the biggest health challenges we face today, including cancer, heart disease, and dementia.
Together with our study contributors, we’ll be investigating how our lives shape our health, immunity, and wellbeing, based around five interconnected strands of health:
Social and health habits
What happens to your body when you sleep?
When we sleep, we go through several sleep cycles made up of four stages.
Stage 1: Dozing off
Your body and brain start to slow down and relax.
You’re easy to disturb and wake up during this stage.
Stage 2: Light sleep
Body temperature falls, muscles relax more.
Breathing, heart rate, and brain activity slow down.
Stage 3: Deep sleep
Your body and muscles relax even further.
There are specific patterns of brain activity known as delta waves in this stage.
Deep sleep is the most important type of sleep for feeling rested and staying healthy.
It’s harder to wake someone up in deep sleep.
Stage 4: Rapid eye movement (REM) sleep
During REM sleep your brain activity increases, almost similar to being awake, while your muscles are temporarily paralyzed.
We have our most intense dreams during REM sleep, and it’s important for learning and memory.
As the night progresses, you have less deep sleep and more REM sleep.
After a phase of REM sleep, you may briefly notice yourself waking up before starting another cycle.
The overall length of each sleep cycle, and the time we spend in each stage, changes throughout the night, and varies from person to person. Your sleep pattern can also differ from one night to the next depending on things like stress, activity, and drinking alcohol.
How much sleep do you need?
The recommended amount of sleep depends on your age. Recommendations for healthy adults are between 7 and 9 hours of sleep per night, while babies, children, and teenagers need more. However, individual requirements are personal and as with nutrition, there’s no one-size-fits-all solution for sleep.
Even though the ideal amount of sleep can vary person to person, as many as 1 in 3 of us don’t get enough. Given how important sleep is, there’s a growing concern around the prevalence of sleep problems and what they mean for our health and how we function during the day.
If you’re struggling with feeling sleepy during the day, check out our tips for boosting your energy.
How does your sleep affect your health?
Like food, sleep is essential for health. Skip a night’s sleep and you'll start to feel foggy and confused, similar to being drunk. You might also get cranky and irritable, feel wobbly on your feet and struggle to communicate.
A further day or two with no shut-eye and you could experience hallucinations and mini-blackouts, known as microsleeps, putting you at high risk of having an accident. An infamous 1989 study even showed that rats would die if they were continuously sleep-deprived, although this is unlikely in humans (except for people with a very rare genetic condition called fatal insomnia).
But you don’t have to miss a whole night’s sleep to have a negative impact on your mental and physical health. Even one or two nights of bad sleep accumulate to make our bodies respond differently to stress and brains underperform. Whether you’re struggling to get through a meeting-heavy work day or noticing out-of-character behavior from tired children, poor sleep leads to harder days.
This only gets worse the longer bad sleep persists. There’s a growing body of research showing that not getting as much sleep as you need over a prolonged period of time (known as chronic sleep deprivation) has wide-ranging effects on the body and brain.
Lack of sleep affects us physically, making us more susceptible to high blood pressure, high cholesterol, heart disease, type 2 diabetes, and many other issues. It also has an impact on mental health and agility, increasing the risk of depression and leading to faster cognitive decline as we get older.
Having poor sleeping patterns is also linked to stress, although it’s hard to disentangle whether a lack of sleep causes stress, if stress leads to problems sleeping, or a bit of both.
How can we study the connections between sleep and health?
Researchers use a range of tools to investigate and study sleep.
The most detailed data on what’s happening when someone sleeps is collected in a sleep lab. Also known as a sleep clinic, this is a mock bedroom in a hospital or research center. People with suspected sleep disorders go to a sleep lab in the evening - bringing their pajamas and toothbrush with them - and sleep there overnight while sensors take measurements of their heart rate, breathing patterns, movement, snoring, oxygen levels, and brain waves.
A less accurate, but easier way to collect data is actigraphy. This is a device similar to a smartwatch and measures rest and activity over time. Here at ZOE, we’ve used actigraphy in our PREDICT studies to explore the impact of sleep on metabolism and health.
We can also use large surveys and questionnaires to study sleep and health. Last year, more than a million of our app contributors responded to our detailed diet and lifestyle questionnaire, helping us to measure just how many people experienced changes to how long they slept during the pandemic.
What has ZOE discovered about sleep and health?
Over the past few years, our research has revealed important insights into sleep and its effects on our health, particularly our metabolism.
It’s been known for some time that sleep quality and sleeping patterns have an impact on blood sugar control for people with type 2 diabetes. However, our PREDICT study showed for the first time that this connection holds up in the general population too.
We found that having a poor night’s sleep or an irregular weekly sleep pattern is associated with a less healthy blood sugar response to breakfast the following morning. Even a small change in someone’s normal sleep pattern, such as staying up late for one night, could affect their metabolism the next day.
Our research also backs up the benefits of an early bedtime. People who generally had a later bedtime, getting less sleep before midnight, were less able to control their blood sugar the next morning, even if they slept in. By contrast, going to bed earlier and getting more sleep before midnight led to better blood sugar control the following day.
We’ve also used the ZOE COVID Study app to find out how the pandemic disrupted people’s sleep, with some people sleeping for longer each night and others for less. We also found that sleeping well and more often is mildly associated with lower anxiety and depression levels. But with 37% of people reporting sleeping less well during the pandemic, it’s clear that many of us struggled to get enough sleep over the last two years.
ZOE's Head of Programs Emily Leeming says "There are a few ways which might be helpful to improve your sleep. Firstly - try and find a sleep routine that works for you, where you are going to bed and getting up at roughly the same time each day and night. Before you go to bed, turn your phone off, blue light exposure is thought to trick your brain into thinking it's still day time. If you're a coffee drinker, try not to drink caffeine too late in the day (after 3-4pm) as it stimulates your nervous system and could be stopping your body from relaxing late at night - or stick to decaf. Caffeine is thought to stay in your system for 6-8 hours."
What do we still need to find out about sleep and health?
Despite all the progress that has been made in recent years, there are still plenty of unanswered questions about the connections between our sleep and our health, immunity and wellbeing. For example: does better sleep improve symptoms of chronic health conditions? How is sleep beneficial for the immune system and what’s the interaction?
Emily Leeming says "having a poor quality or disrupted sleep may mean that the following morning your body struggles to handle its blood sugar levels as well. This might mean while you may feel like reaching for something sweet and comforting for breakfast, choosing a healthy option, such as eggs on rye bread with avocado, might make you feel more energetic during the rest of the day".
ZOE’s large-scale, data-driven approach offers a powerful way to find answers to these questions and more, not just for sleep but across all five strands of health.
Our Wider Health Studies aim to connect each of our personal health journeys to patterns in the wider population, revealing new insights into health and disease that could help us all lead healthier, happier lives.
Together, we’re changing the future of health research. To get involved, simply download the ZOE app, fill in your health profile, and get in the habit of logging daily health reports. We’ll be adding new studies and research activities as we bring them online, so watch this space for updates.
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Explore the ZOE Health Academy to learn more about the science of nutrition, healthy living and immunity.