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Why we sleep and how it affects your lifespan.

Most of us know that a good night’s sleep is important for our wellbeing, but in a western culture that champions productivity and efficiency many times our sleep time is the last priority or something that we can catch up on later. Humans and mammals spend about one third of our lives asleep, in a state that renders us vulnerable and unable to do more productive things like hunt and feed - if sleep wasn’t absolutely essential animals would have evolved differently.


So why do we sleep? During sleep the glymphatic system in the brain flushes out all the waste produced during the waking hours. Some of these waste products include amyloid-beta and tau proteins. Tau is a protein that is found in patients with Alzheimer’s disease. One of the theories of what causes neurodegenerative disease is that the build up of waste products causes neuroinflammation, which causes damage to the neurons in our brain and leads to cognitive impairment. Poor sleep especially in middle age is associated with an increased risk of Alzheimer’s disease. Patients with neurodegenerative disease also have trouble sleeping which leads to a vicious cycle. Another important function performed in our brains when we sleep is the consolidation of memories and maintaining our ability to correctly interpret facial expressions. Sleep deprived people interpret friendly faces as a threat, and are unable to heal emotionally from traumatic experiences. This is one of the causes of PTSD in war veterans.


Developing brains also need more sleep than adult brains. In a study of more than 8000 children, sleeping less than 9 hours a night disrupted areas of the brain involved in behaviour, memory and learning. These children had a higher incidence of behavioural problems and learning difficulties.


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Why we sleep and how it affects your lifespan
Sleep deprivation causes a rapid decline in health. Acute sleep deprivation, even a week of 4-6 hours of sleep per night, has a significant impact on appetite, performance, mood and cognition. In the long term, chronic sleep deprivation is associated with cardiovascular disease, high blood pressure, Alzheimer’s disease, poor mental health, decreased immune function, and increased cancer risk.

Poor sleep leads to activation of the sympathetic nervous system - our fight or flight response and release of a hormone called cortisol. This leads to an increase in blood pressure and raised heart rate. If this continues for a long time for example in people who are chronically underslept, this increases damage to arteries and explains the increased incidence of heart attacks and strokes. Additionally, the cascade of hormone imbalances resulting from poor sleep increases ghrelin - our hunger hormone, which causes us to be hungrier and make poor food choices like eating junk food.


How many hours should we sleep? 7 - 8 hours a day is recommended, ideally going to sleep at the same time of day. Interestingly, too much sleep (consistently sleeping over 9 hours) is associated with increased mortality.


Sleep deprivation also causes a rapid deterioration in a host of mental health issues including increased anxiety, depression as well as suicide. Sleep and mental health is actually a two-way relationship - people with sleep problems are at an increased risk of developing certain mental illness, and people with psychological disorders are more likely to develop sleep problems.


Establishing good sleep hygiene promotes good sleep quality and duration. The following are some of the key practices and behaviours we should incorporate into our daily routines in order to optimise sleep:

  1. Regularity - try and keep to a daily, consistent sleep schedule (you cannot make up for lost sleep during the week over the weekend).

  2. Light - sleep in a dark room and be sure to get sunlight exposure daily in order to help keep a circadian rhythm.

  3. Temperature - your core body temperature needs to drop to induce sleep - sleep in a cold room. Having a hot bath before bedtime may also help lower your body temperature.

  4. Stimulants - avoid caffeine and alcohol close to bedtime.

  5. Do not lie awake in bed for too long.

  6. Establish a wind-down routine such as meditation.

  7. Remove clock faces to avoid anxiety of not falling asleep.

  8. Remove technology from the bedroom - blue light from phones suppresses the release of the hormone melatonin.






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