Sleep matters. Estimated annual economic loss due to sleep problems in the U.S., Canada, UK, Germany, and Japan is approximately $680 billion and the effect on how long we live and the quality of our time is now very clear.
Our body clock and the sleep-wake cycle are what we call the circadian (24h) rhythm and it is crucial to good physical and mental health. During the day, toxins accumulate from physical activity and cell damage. Sleep provides the time needed to clear these toxins and an opportunity for the immune system to be much more active.
Many immune functions operate in tandem with this 24-hour sleep–wake cycle. Hormonal fluctuations support cell growth, tissue repair, and restoration whilst asleep. Whereas being awake is associated with anti-inflammatory activity this ‘inflammatory peak’ happens during nocturnal sleep.
We need sleep to boost our immunity. Sleep enhances immune responses against acute illnesses, such as viruses and because inflammation causes fatigue, immobility, pain, and other aspects of illness, it makes sense to confine inflammation to sleep.
We also know that reduced sleep quality increases the risk of infection and poor infection outcomes. Humans who habitually sleep for less than 5 hours a night (compared with 7–8 hours) are more vulnerable to respiratory infections, and are at increased risk of common illnesses, including cold, flu, gastroenteritis, and other common infectious diseases.
But it doesn’t just boost immunity in the short term, sleep also enhances long-term protection. We know that it regulates factors contributing to the development of chronic diseases such as cardiovascular disease, type-2 diabetes, asthma, reflux, migraines, obstructive sleep apnoea, and Alzheimer’s disease.
A study of 90,000 people in the UK found that those who went to bed between 10 and 11 pm were 25% less likely to develop heart disease than those who regularly went to bed after 12 am.
This may also be because blood pressure (BP) typically decreases during sleep as the nervous system becomes less stimulated and adjusts to the expected pressure of the blood when lying down. Sleep deprivation leads to increased blood pressure, and even half a night of sleep loss can increase BP in people with hypertension or pre-hypertension. Even periods of just 10 days of sleep deprivation lead to raised blood pressure, and people sleeping <6 hours per night are 66% more likely to have hypertension than individuals obtaining between 7-8 hours per night.
So, if we accept that sleep is crucial for immune function and lowering disease risks, you might wonder why this is the case.
Firstly, during sleep deprivation, white blood cells and other markers of inflammation increase to a range associated with the development of cardiovascular disease. We also know that some major markers of inflammation have been found to increase during sleep deprivation and are independent predictors of a first cardiovascular event in apparently healthy individuals.
Secondly, how we use glucose slows down during sleep deprivation, and this increases the risk of insulin resistance and diabetes. The quantity and quality of sleep consistently and significantly predict the risk of developing type 2 diabetes.
During sleep deprivation, leptin(a hormone that tells your brain you’re full) is reduced, whilst Ghrelin, a hormone that signals hunger, is increased. This increases appetite and cravings, especially for higher carbohydrate foods, and is strongly linked to weight gain. Getting more sleep results in better weight loss, regulates appetite, and improves alertness and mood.
There is a clear link between poor sleep and poor mental health, and we know that night owls are more likely to suffer from neurological and psychological problems.
We now know that whilst asleep, we not only lay down memories but also solve problems! We don’t have the cognitive capacity to process everything when we are awake, so we store it and process it when our senses are at rest.
Sleep loss causes more fluctuant mood, increases irritability, reduces empathy, and increases the risk of depression, anxiety, and bipolar disorder. In patients with insomnia, the prevalence of anxiety, panic disorder, PTSD, and depression is raised by up to 31% and research shows that stabilising sleep can improve all these conditions – sleep is a form of therapy.
Why could this be? It seems the tired brain forgets positive experiences more easily than negative ones and is less capable of multi-tasking and ordering tasks, so we tend to hyper-focus on one thing – this may be one benefit (but is not without its risks).
We also see that around 90% of patients with depression complain of sleep disturbance, and sleep problems are much more common in those with anxiety disorders. Moreover, insomnia increases alcohol use as well as socio-economic problems.
The expectation of having 8-9 hours of uninterrupted sleep is a relatively recent invention and is not based on sound science – we used to sleep when it became dark and then awaken during the night, and again at dawn. The National Sleep Foundation has sleep duration guidelines which recommend 9-11 hours for school-age children, 8-10 hours for teenagers, 7-9 hours for adults, and 7-8 hours for adults over 65.
7–9 hours is appropriate for adults to promote optimal health and reduce the risks of diseases such as high BP, diabetes, and obesity. Less than 6 or more than 9 hours increases the risk of cardiovascular disease, diabetes, and obesity – everything else being equal, you are more likely to die if you sleep too little or too much.
People who report sleeping 9 hours or more per night report 15% less physical activity per week than those sleeping 7 to 8 hours per night. So, you move less when you sleep more – makes sense and this may be one reason why these risks increase when sleeping more than 9 hours a night.
And things are changing – in 1959, adults slept 8 hours per night on average. By 2002, this had decreased to 7 hours per night, with more than one-third of adults sleeping fewer than 7 hours.
Current studies show that 43% of adults report that they often stay up later than they should, watching television or using the internet, and 45% report that they sleep less to get more work done.
Reading this article has already improved your sleep! Research indicates that sleep education improves sleep quality and duration – simply learning about sleep helps alleviate symptoms in and of itself. So, pat yourself on the back and read about what else you can do to sleep better.
Download our 30-minute bedtime routine here. 30-minute bedtime routine
The right time to ask for help is whenever you or someone who cares about you thinks you need it. Find the time to get some advice, learn what works, and plug into useful online materials and apps that help with regulating your sleep cycle and improving the chances of refreshing sleep.
Relevant internal links
External resources used for this article
The Role of Magnesium in Sleep Health
Sleep Health Promotion Interventions and Their Effectiveness: An Umbrella Review
Association of Sleep Time With Diabetes Mellitus and Impaired Glucose Tolerance | Sleep Medicine
Role of sleep deprivation in immune-related disease risk and outcomes
How Much Sleep Do You Really Need?
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