'Why Sleep Matters’
Sleep is one of the most important aspects of our life, health and longevity and yet, it is increasingly neglected in 21st century society, with devastating consequences. Every major disease in the developed world – Alzheimer’s, Cancer, Obesity, Diabetes – has a very strong causal link to deficient sleep. Until very recently, science had no answer to the question of ‘Why we sleep’, ‘What good it serves’, or ‘Why its absence is so damaging to our health’. Compared to the other basic drives in life – eating, drinking, and reproducing – the purpose of sleep remained elusive.
Sleep is a complex process during which our body undertakes a number of essential activities. It involves low awareness of the outside world, relaxed muscles, and a raised anabolic state which helps us to build and repair our bodies. Primarily, sleep is for the brain, allowing it to recover and regenerate. During sleep, the brain can process information, consolidate memory and enable us to learn and function correctly during the daytime. Whist we sleep, our brain is not only strengthening memories but it is also reorganising them, picking out the emotional details and helping us to produce new insights and creative ideas.
Sleep affects our ability to use language, sustain attention, understand what we are reading, and summarise what we are hearing. If we compromise on our sleep, we compromise on our performance, our mood, and our interpersonal relationships. Sleep also has been shown to protect the immune system.
Animals have evolved to sleep in many different ways. Dolphins can sleep using only one half of their brain at a time. Even hibernating animals have been shown to temporarily cease hibernation, go to sleep, and return to hibernation. Sleep is an inconvenient, time consuming process, but it is so essential that we simply evolved to fit it into our lives.
How Much Sleep Do We Need?
We all need different amount of sleep. In humans, the amount of sleep that you need generally depends on your age. New born babies tend to sleep for an average of 16-18 hours per day, which decreases to about 13-14 hours after one year. Adolescents tend to require more sleep than adults, possibly due to the physiological changes that are happening in the body during this period. Adults will tend to sleep 7-8 hours per day, with older adults sleeping roughly 6-7 hours per day.
Still, it is important to gauge the amount of sleep that we need and to ensure that we get the right amount. There is no set amount of sleep that is appropriate for everyone. Sleeping less than we need to as individuals has negative consequences. Whilst awake, we build up a sleep debt that can only be repaid through sleeping. This is regulated by a mechanism in the body called the sleep homeostat, which controls our drive to sleep. If we have a greater sleep debt, then the sleep homeostat indicates to us that we need more sleep. However, it’s worth highlighting that it’s not as easy as sleeping in at the weekends to make up for sleep lost during the week. Research suggests that it can take up to four days to recover from an hour of lost sleep.
Sleep Patterns
Equally important as the total amount of sleep is the pattern of sleep. Babies and small children tend to sleep multiple times across each 24-hour period, but as we mature into school years and adult life, we tend to sleep in one long phase; daytime sleeping decreases and the person instead tends to sleep throughout the night.
A mechanism called the Circadian Rhythm regulates the pattern of our sleep and waking, and interacts with the sleep homeostat. Most living things have internal circadian rhythms, meaning they are adapted to live in a cycle of day and night. Think of it as a ‘master clock’ that regulates our circadian rhythms. This clock is made up of a group of nerve cells in our brain called the suprachiasmatic nucleus (SCN). The SCN controls the production of melatonin, which is a hormone that makes us feel sleepy. During sleep, melatonin levels rise sharply. The SCN is located just above our optic nerves, which send signals from the eyes to the brain. Therefore, the SCN receives information about the amount of light in the environment through our eyes. When there is less light, such as during the night, it tells the brain to create more melatonin.
Serotonin is another chemical that affects sleep; produced by the brain, insufficient levels of serotonin are also related to mental health problems such as depression and anxiety. Levels of serotonin are highest in the brain when we are awake and active, and the brain produces more serotonin when it is lighter outside. This is why most people feel tired at night-time, and why it is a good idea to turn off the lights when we are trying to sleep. The immune system also influences serotonin, and therefore sleep patterns, which may explain why we need more sleep when we are feeling ill.
Some people function best in the mornings, others best in the evenings, some are somewhere in between.
Sleeping Well
Most people could benefit from improving the quality of their sleep. The phrase ‘sleep hygiene’ is used to describe how lifestyle and environmental factors can affect our sleep. Positive sleep hygiene may help to improve sleep quality, but is not enough to treat chronic insomnia.
Caffeine, alcohol and nicotine are all substances which can impair sleep quality. Caffeine makes it harder to sleep because it stimulates the central nervous system, increasing your heart rate and adrenaline production, and also suppressing melatonin production. It takes as long time for the body to break down caffeine, so drinking coffee during the day can affect sleep at night.
Alcohol can help people to fall asleep, but it also impairs sleep quality during the second half of the night, and it is a diuretic which means that we may need to wake up in the night to go to the toilet, thus disrupting the sleep pattern. However, a rapid reduction in alcohol intake for someone who is a heavy drinker can lead to alcohol withdrawal symptoms, which can lead to insomnia. Alcohol can also contribute to a depressive mood, which in turn can contribute to insomnia.
Nicotine may impair sleep; smokers take longer to enter sleep and gave less total sleep time compares to those who have never smoked. Reducing nicotine intake is unlikely to lead to immediate sleep improvements, but the long-term health benefits are likely to have implications for sleep quality.
Eating habits also have the potential to affect sleeping. It is important not to go to sleep whilst feeling hungry, so eating a light snack before bedtime might be helpful. However, eating large meals shortly before bedtime should be avoided because the body will spend more time digesting before it can sleep. Some foods may have sleep inducing properties, for example, rice and oats may contain small amounts of melatonin, which increases the desire to sleep. Some foods, such as dairy products, contain the amino acid tryptophan which is useful in melatonin synthesis.
Other foods, such as those that contain caffeine or large amounts of refined sugar make sleeping more difficult. A study in the Isle of Wight examining the effects of food additives on health, found that preschool children who received additive-laden drinks were more hyperactive than when they did not have drinks containing artificial colours and preservatives, meaning they had difficulty going down for a nap.
Regular exercise may also help us sleep. It may be that physical fitness with increased metabolism is associated with better sleep patterns. The timing of physical activity is however very important. Exercise earlier in the day is better for people who want to improve their chances of sleeping, since the short-term effects of exercise include an increase in adrenaline production.