The Physiology of Sleep

Relax, this is not a biology lesson but it is worth reading this article so you can understand the relationship of sleep and the effect it has on our body from all perspectives. Knowing these little nuggets of information makes a lot of sense when you are trying to sort elements of our life. Every thing from weight control, stress management and overall happiness can all be tied into our quality of sleep. There are many factors that contribute to our wellbeing. Some are within our control and others are not. Genetics, lifestyle choices, careers, stress, overall happiness in life, relationship status, pain, grudges, and general health all lead to the quality and quantity of our sleep. It is essential for not only our physical and psychological but also physiological well being.

I have included a quick overview of the physiology side of sleep to give you a better understanding of how our body works and the contributing factors to our lives.



Genetics will contribute to our ability to sleep well. The jury is still out on if our DNA makeup predisoses us to insomnia. Scientists indicate some people’s genes increase their stress-reactivity. This increased stress response predisposes them to the likelihood of poor sleep and developing insomnia. Ironically, poor sleep may disrupt the normal function of the genes, leaving many caught in a sleep-deprived vicious cycle. This may be difficult to change although don’t lose heart there are strategies that will help. Hormones are also contributors to how our body behaves. Humans produce certain hormones that contribute to our sleep quality, coping abilities and weight control. Hormones such as melatonin, cortisol, Leptin and Ghrelin are produced by the body and there is an enormous amount of information on the internet supporting why and how these hormones affect us so it is not my intention to bore you with a biology lesson.  Lack of sleep affects the body’s ability to regulate hormone secretions and work optimally. There is however such a thing as to much sleep causing adverse affects on the  body. I will discuss this more in the Sleep habits section

Included in this section is a quick overview so you understand that there is some science behind how our body behaves although the objective of this  is to help you introduce strategies to improve your overall sleep and quality of life.

Circadian Rhythm


The circadian rhythm is our natural 24 hour body clock and controls all of our bodily functions.  Hormones, appetite, body temperature, metabolism, awake/sleep patterns, gastrointestinal regulation, cardiovascular health and overall well being are all regulated by our body clock.

It is regulated by light and dark, temperature and external influences in our daily lives. The circadian rhythm dips and rises at different periods throughout the day and this will alter in each individual. Shift-work, frequent travel and technology all compromise our natural synchronicity which is vital for physical and mental well being


Melatonin is commonly known as the sleep hormone. It is produced by the pineal gland and is dormant during the day. As night falls the pineal gland starts up and begins to produce the hormone. As a result the melatonin levels begin to increase resulting in the feeling of sleepiness. The levels usually stay in the body for about 12 hours although the levels reduce as the night goes on.  The production of this hormone is usually controlled with light and dark although the release times can vary depending on our lifestyles, age or nocturnal habits. Forms of technology such as computer or television screens or bright fluorescent lighting can delay the release resulting in the lack of sleepiness resulting in us going to bed later.


Body Temperature

The circadian rhythm along with our sleep hormone, Melatonin contributes to the natural rhythm of our 24 hour temperature cycle. Our core body temperature fluctuates through the day and greatly affects the ability to initiate sleep and maintain sleep. It is always easier to fall asleep with a cooler body temperature. Our body temperature reduces whilst we sleep. It is also important to ensure you are comfortable in bed with the correct bedding. If you are too warm or too cold, you will not sleep soundly and will more than likely wake often leading to sleep deprivation.

Sleep / Wake Homeostasis – Sleep Drive

Our sleep drive is produced by a natural chemical produced in our brain called Adenosine that helps balance the natural sleep/wake rhythm. It commences being released when we wake in the morning and continues to increase throughout the day creating our need for sleep. This build up during the day results in sleepiness and is an indicator to our body of the time to go to sleep. The Adenosine dramatically falls once the onset of sleep takes place. This is why stimulants such as caffeine in coffee, tea, cola and energy drinks are discouraged from late afternoon as they work as a natural blocker inhibiting or dampening the sleepiness effect, thereby increasing alertness, particularly if you are hypersensitive to the affects of caffeine.


Cycle of Alertness

This is part of our circadian rythm. It is normal to have alertness peaks and lows during the day which are regulated by our circadian rhythm. These peaks and troughs occur at regular times of the day although external stimulus such as the time you ate and the task you are doing at the time can vary these periods for each individual. If you are doing a task that is sedentary such as watching TV or working on a computer in the mid afternoon it is normal to start to feel dozy where as if you were doing something active such as working in the garden or running around at work you may not experience this lull.


Cortisol is produced by the adrenal glands and should be lower at your bed time. The levels slowly decrease as the night draws on.  Higher levels of Cortisol are common in people who display signs of stress although defining stress can be difficult as each person deals with stress in our own way. High levels of stress has been shown to contribute to weight gain and loss of libido or insomnia.

Image ref:

Leptin and Ghrelin

Putting on weight when your sleep deprived?  2 appetite regulating hormones, Leptin and Ghrelin play a vital role in stimulating or suppressing our appetite. Leptin is a hormone produced in fat cells in our bodies and its job is to suppress hunger. Ghrelin is produced in our digestion system and it is designed to stimulate our appetite. If you compromise your sleep, you reduce the levels of leptin produced which then causes an imbalance resulting in stimulating us to eat. The compromised leptin level is out of balance with the level of ghrelin so the brain continues to send the message that you are hungry resulting in over eating and weight gain

It has now been documented from studies the correlation between people who sleep less hours carry a higher body fat or BMI.

Developing the habit: 

Sleep requirements are highly individual. Where one person may cope very well on 4-5 hours sleep a night others may require 7 -9 hours or more to cope with their day. The amount of sleep required and the quality of sleep can change from day to day, depending on factors like stress, lifestyle habits or illness. So trying to give an answer to the question “how much sleep do we need each night?” is like defining how long is a piece of string. The general rule is 7 – 9 hours in adults.

It is recommended to test the effectiveness of sleep on your body to work out how much sleep you, as an individual needs. Try sleeping for 7 hours for a week and note how you feel during the day. Slowly increase it by an hour each week and whichever time frame you feel better on is your sleep number.

Having said that there are definite gauges we can use to measure how much sleep we need to perform at our optimal best. Optimal best encompasses all aspects of our being including our weight. You may display signs in some or all of the indicators below.


  1. Physical:

How are your energy levels throughout the day?  If you exercise, are you just going through the motions or putting in serious effort? Are you having periods of sleepiness during the day whereby given the opportunity, you would certainly close your eyes and nap?

  1. Cognitive:

Brain function is seriously compromised when we are sleep deprived. This can be very obvious just trying to hold a general conversation. Our ability to recall words in conversation, processing, comprehension and retaining of information can be seriously affected. You may notice it in the attention to details when performing routine tasks and memory

  1. Personality:

The ability to cope with sudden changes or stress is another obvious gauge. Mood swings or a tolerance within certain situations can be affected.


  1. Health: Organ and Physical

Repetitive illness is a clear indication. Without adequate sleep our bodies become run down which in turn reduces our immunity to common illness such as cold and flu.Your immune system relies on good quality sleep to enable it to function at its optimal best. Sleep deprivation leads not only to low resistance to fight illness but also contributes to our natural ability to fight illness and recover quickly.

Quality sleep contributes enormously to how our  vital organs regenerate damaged cells and blood vessels, optimal blood circulation, toxin removal,  healing and repair. Sleep deprivation increases risk of heart disease, diabetes, bladder issues  and respiratory health

  1. Weight

The amount of sleep we have or rather lack thereof can affect our weight. Sleep deprivation will make us lazy so our food choices are compromised but also sleep deprivation affects our metabolism and the productivity of our digestion system.


6.  General well being and happiness.

One of the first things we let go of when we are stressed or have work commitments is our sleep.  We forgo sleep to meet our deadlines and then slowly but surely for many, this leads to a breakdown in the everyday routines. The loss of  sleep usually gets made up on the other end so instead of getting out of bed and doing exercise and being organised we relinquish our habits which in turn adds to our internal stress. We get frustrated with ourselves, feel less active. If we dont stop and pay attention to this it may lead to signs of depression or developing these bad habits.

Sleep needs to be given the level of importance it deserves because it is a huge contributing factor on how we conduct our lives.

http://Refer to our  Sleep Strategies page for comprehensive hints to assist you if you have problems with initiating sleep and / or staying asleep.

Summary of our physiology that controls our sleep / wake patterns


Return to world of sleep