Until recently sleep was thought of as a passive process in which our body shuts down our physical and mental functions in order to recuperate from our daily activities.
Advances in sleep science have shown that sleep is far from being passive and is in fact an active and complex process that is crucial in preventing diseases and pathologies, regulating our metabolism, forming memories, maintaining your physical health and wellbeing and removing toxins from the brain.
Given these important functions the consequences of a lack of sleep become apparent as sleep is critical to all the bodies essential processes.
There are four stages of sleep, N1, N2, N3 and REM and each cycle takes approximately 90 minutes to complete. The full sleep cycle takes approximately 7-8 hours so this is the recommended minimum amount of sleep that is recommended so that we are not interrupting the natural sleep cycle.
Each stage in the sleep cycle performs extremely important and distinct physiological and phycological functions.
In the N1 stage the core body temperature begins to drop and the muscles relax. This is a very light sleeping stage where people can be aroused quite easily. People often experience hynic jerks or a sensation of falling which scientists believe is something we have retained from when our ancestors slept in trees as a protection against falling.
The N1 stage is important as a transition into sleep and normally only last about 10 minutes before moving onto stage 2.
In a normal sleep pattern we will spend around half of our time on stage 2. The heart rate drops, muscles relax further and brain wave activity decreases apart from very brief spikes called spindles which are important in organising memories for long term storage. It is thought that an increase number of spindles is associated with intelligence representing the need to store increased amounts of recently acquired information. Disruption to N2 sleep stage may be indicative of sleep apnea, restless leg syndrome, or chronic insomnia.
Phase 3 is a deep sleep stage. Getting to this stage is very important for the body as is evident from the physiological changes that occur in this stage.
There is a reduced blood flow to the brain in order for it to recover and maintain normal body functions. Hormones are released to maintain appetite control, blood flow to muscles increase in order for the muscles to recuperate from the days activity and receive more oxygen and nutrients. The pituitary gland releases growth hormones at this stage which results in growth and repair of muscle bone and various other tissues. This stage is also critical to strengthen and support the immune system.
With all these important functions performed at this sleep stage its clear how important it is for our bodies and how it would suffer from not getting this full stage of sleep as often as possible.
Interestingly, when we are sleeping in an unfamiliar environment our brains will resist the temptation of going into the N3 or deep sleep stage and only one half of the brain is activated for sleep which is another evolutionary response to protect from potential dangers.
The fourth and final sleep stage is the REM sleep stage characterised by rapid eye movement, vivid dreams and paralysis of the body’s muscles. In contrast to the other sleep stages your body temperature rises, blood pressure rises and your heart rate and breathing increase. Whilst the other stages are important for the body it is though that the REM stage is important for the mind. It plays a critical role in brain development as well as being especially important for mood and memory.
What are the effects of sleep deprivation?
Learning & memory
Sleep deprivation has a profound effect on our ability to learn and to retain memories. The hypocampus area of the brain acts like an inbox for our memories and in the N2 phase of sleep memories get transferred from short term fleeting memories to a long term storage that can be recalled at a later date. Brain wave scans on brain activity shows a hive of activity at this area of the brain during the N2 phase of sleep and no activity at all in sleep deprived individuals. Studies have shown a massive 40% decrease in memory and learning outcomes on people who had a good nights sleep versus those that are sleep deprived. (1)
A 2014 U.S, study (2) showed that after daylight saving time in the Spring, and the associated disruption to sleep, raised the risk of having a heart attack the following Monday by 24%. It also showed that when daylight saving time is reversed in the Autumn there is a 21% reduction in heart attacks the next Monday. The cause of this is that day light saving time cause a disruption to the circadian rhythm and subsequently affects the quality of sleep which increases inflammatory cytokine levels raises blood pressure and heart rate and can be a trigger of heart attacks.
Reducing sleep to four hours a night causes an astonishing 70% reduction in our natural killer cells(3) which are crucial for identifying and eliminating unwanted toxins and pathogens and maintaining a healthy immune system. If this is maintained over time it put our bodies in a much weaker position to fight off disease and to remain in a healthy state.
Certain cancers and precursors of cancers have also been linked to a lack of sleep duration(4) (5) and interestingly some cancers such as colorectal cancer have been shown to occur more often in people with very long sleep durations (6) so getting a balance of 7-8 hours sleep is important. The WHO has listed sleep deprivation from shift work as a possible carcinogen.
A crucial aspect of health a wellness in men is their testosterone level. It has been shown that men who sleep five hours or less a night have significantly smaller testicles than those that sleep seven hours or more! They also produce less testosterone, as testosterone is predominantly released during sleep, and can have levels of a man ten years older.(7) We have also seen similar impairments in female reproductive health that is caused by a lack of sleep. Genetic studies (8) have shown that sleep deprivation causes a distortion in activity of 711 of our genes. Those genes that were down regulated or turned off were associated with the immune system and those that were up regulated or turned on were associated with the formation of tumors, stress and long-term chronic inflammation.
The importance of melatonin for sleep
Melatonin is a sleep hormone produced by the pineal gland that regulates the sleep-wake cycle. It is released in response to progressive darkness and results in an increase in sleep propensity at night time. Under normal circumstances it reaches a maximum blood concentration at around 2 or 3am.
Artificial light and in particular blue light from screens have been shown to inhibit the production of melatonin and cause a disruption to the circadian rhythm and natural sleep-wake cycle. Melatonin also plays an important role as an anti-oxidant which protect us from free-radicals that have a role in heart disease, cancer and other diseases. It’s anti inflammatory effects also plays an important role in the immune system. Blue light has been shown to inhibit the production of melatonin from the pineal gland and disrupt the circadian rhythm. Digital screens emit high energy blue light so it is recommended not to use smartphones, tablets or laptops in the hour or two before bedtime or if you are going to use them to use blue light blocking glasses to help prevent this inhibition of melatonin production and to get a good nights sleep. The blue light can inhibit the production of melatonin by up to three hours and your peak melatonin levels will be 50% less. Throughout our history midnight was traditionally the middle of our nights sleep but it has now become the time that we check our facebook and Instagram accounts which is detrimental to getting a good nights sleep due to the blue light exposure. You can get more tips on how to get a good nights sleep here.