SLEEP, THAT GREAT SCULPTOR
To understand why sleep is so important, think of the body as a factory that performs various vital functions. When we fall asleep, our body starts to:
- Restore damaged cells
- Strengthen the immune system
- Recover from the day's activities
- Consolidate memory
Understanding the sleep cycle
Understanding what happens during sleep also means understanding the sleep cycle, which consists of two recurring phases: REM (rapid eye movement) and NREM (non-REM or non-rapid eye movement). Both are fundamental and perform important, but different functions.
NREM sleep normally makes up 75-80% of our total sleep each night. Many of the health benefits of sleep occur during NREM sleep: the growth and repair of tissue, the restoration of energy, and the secretion of hormones essential to our body.
REM sleep typically makes up 20-25% of our total sleep each night. Where most dreams occur, REM sleep is essential for our minds to process and consolidate emotions, memories and properly manage stress.
Quality sleep, with its various phases occurring in harmony, is vital for learning, creativity, interpersonal relationships and for both physical and mental health.
Repeated interruption of REM and NREM cycles during the night – whether due to breathing difficulties or to frequently waking up – compromises vital bodily processes and can affect health and well-being both the following day and over the long term.
What happens if you don't get enough sleep?
If the body does not get an opportunity to sleep properly (going through the full REM and NREM cycles) we start the next day at a disadvantage, putting our health at risk. We compromise cognitive functions such as learning and memory; and we increase the risk of obesity, type-2 diabetes and hypertension, with negative impacts on heart health.
Two systems interact every day for sleep to happen properly: homeostasis, which is responsible for creating our body’s desire to sleep; and circadian rhythms, which organise our sleep time..
Sleep-wake homeostasis is a biochemical system that promotes the accumulation of sleep-inducing substances in the brain. This system works as a timer, generating homeostatic sleep; that is, it exerts pressure on the body to sleep after we have been awake for a certain amount of time. For this reason, the longer a person is awake, the stronger their desire to sleep becomes..
Circadian rhythms are our internal clock, responsible for regulating and coordinating the body's biological processes and alertness levels. This regulation makes it possible to control sleep times according to the light-dark cycle of day and night. In addition to the sleep-wake cycle, circadian rhythms are also responsible for regulating feeding patterns, body temperature, brain wave activity and hormone production during each 24-hour period..
Sleep and its impact on our health
Learning, Memory and Performance
Sleep assists learning and memory through two processes: facilitating voluntary attention, and consolidating memories for effective learning.
Without adequate sleep, exhausted neurons are unable to efficiently receive external stimuli, adequately coordinate information, or access previously acquired memories.
Lack of sleep affects mood, motivation, judgement and perception of events, affecting decision-making.
Chronic tiredness to the point of fatigue or exhaustion means that we are less likely to perform well. Neurons do not fire optimally, muscles are not rested, and organic systems are not synchronised.
Risk of obesity and type-2 diabetes.
During sleep, our body produces hormones that help control appetite, energy metabolism and glucose processing. Insufficient sleep leads to increased production of cortisol (the stress hormone), increased insulin secretion, a deficiency in leptin metabolism (the hormone that signals when you have had enough food) and the production of higher levels of ghrelin (a biochemical substance that stimulates appetite).
As a result, insufficient sleep can lead to weight gain, excessive craving for food, and the desire for higher-calorie foods. In addition, insufficient sleep leaves us too tired to burn the extra calories with exercise.
Heart disease and hypertension.
Even short periods of inadequate sleep can cause an increase in blood pressure.
Insomnia and other sleep disorders such as Obstructive Sleep Apnoea are strong risk factors for cardiovascular diseases.
People with sleep apnoea usually wake up several times a night as a result of airway strangulation while they are asleep, accompanied by brief bouts of hypertension each time they wake up. Over time, this can lead to hypertension, which is an important risk factor for cardiovascular disease.