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  • Writer's pictureKim Atherton

Stress, Cortisol, Sleep & HPA Axis

Updated: Dec 12, 2023

Stress, Cortisol and Sleep. What is the relationship between them? Cortisol is a vital hormone our bodies require to protect us and keep us safe. It relies on sugar (glucose) to function, hence it's called a glucocorticoid. It also manages glucose, fat and protein metabolism in the body. Cortisol is made in our adrenal glands.


Cortisol, the HPA Axis, Sleep and Stress Interactions


What does cortisol keep us safe from? Stress. Stress can be real or perceived. It can also be exogenous (outside the body) or endogenous (inside the body). Our brain's Hypothalamus perceives stress (this is where the 'H' in HPA axis regulation comes from).


Firstly, the hypothalamus sends direct messages to our sympathetic nervous system (SNS) to either run away or get ready to defend against the enemy (stress). This is called the 'Fight or Flight' response. Adrenalin and Noradrenalin get released from the adrenal gland in this manner and act on our organs so we can defend ourselves, or run away. This can even be from perceived nasty comments. This electrical response is signaled from our nervous system so the response is immediate.


Secondly, the hypothalamus also sends a chemical message to the pituitary gland ('P' in HPA axis) which releases a hormone called ACTH that then acts on our Adrenal Glands (the 'A' in HPA axis). Cortisol gets released from our adrenal glands into our bloodstream and acts on our organs. This hormonal response is via our endocrine system releasing so the response is slower (as compared to the above nervous system electrical response).


This fight or flight response with SNS engagement and our HPA axis response is entirely appropriate if we need to react quickly to a real stressful event. This is an acute response. However, if the daily grind and stress of modern life is relentless, we can operate in a prolonged Fight or Flight mode and have elevated cortisol levels long term. This is not desirable.


Examples of long term stress include exogenous stressors like impaired work-life balance, relationship issues, poor dietary choices, poor water intake, toxin exposure, medications, traffic etc. It can also be endogenous stressors like blood glucose issues, illness, inflammation, endocrine disruption, nutrient deficiencies, dehydration, poor breathing, autoimmunity etc.


Cortisol is present short term in a good way to counteract the effects of stress - to 'put the fire out' and 'rescue us and keep us safe'. If cortisol is present long term, we can have multiple impacts on our bodies.


Long term Cortisol impacts

  • Digestive issues (constipation, diarrhoea, reflux and heartburn, GORD)

  • Weight gain (especially around the middle) and inability to lose weight as cortisol promotes fat storage and triggers unhealthy food cravings

  • Lowered immunity allowing you to get sick more often

  • Diabetes

  • Insulin resistance

  • Irregular periods, heavy periods, low libido, infertility, ovulation issues

  • Chronic fatigue

  • Elevated blood pressure and heart rate

  • Hair loss (from constant erect hair shafts)

  • Dilated pupils

  • Leaky bladder

  • Shallow, rapid breathing with breathlessness

  • Insomnia, sleep apnoea

Exercise as a Stressor


Another stressor is 'really intense' exercise if it is perceived by your body as intense. Have you ever wondered sometimes why the harder you work at exercise, the less it is helping you and your weight loss goals. Gentle exercise that is weight bearing to invoke muscle strengthening may be better suited. Exercise in the 'Goldilocks zone' - not too much and not too little, may be better.

Picture showing Fight or Flight Response and where hormones get released and  impacts on various organs of body
How the Fight or Flight Response works and its impacts on our bodily functions.

Rest and Digest


When the SNS is not activated by stressors we can engage with the Parasympathetic Nervous System (PsNS). This system allows us to 'rest and digest'. This is vital to managing digestive issues and the reason we are advised to relax when eating with family and friends, and not at a work desk, or in front of a laptop, or scrolling through your phone.


Irregular Sleep as a Stressor


An irregular sleep pattern is also a stressor. Our adrenal glands love routine and a regular 'go to bed and wake up pattern' is great for regulating sleep, and allowing cortisol to relax. Light of any form stimulates cortisol to do its normal job which is to get us up and functioning for the day. If it's gentle sunlight waking us up at a predictable time in the morning, then the cortisol level rises within expected levels and primes us for our day ahead. If it's the light of a laptop or mobile phone at 11pm at night when cortisol levels should be low allowing us to sleep, then cortisol will potentially not 'wind down'. If you have to work in the evening then wearing blue blocker glasses can lessen the impact.


It is preferable to be asleep before 11pm at night so our body can physically and psychologically repair. Physical repair is physically repairing our DNA, and ridding the body of waste produced during the day. The long term effects of not looking after your DNA can be disastrous. Sleep is also one of the best things you can do for weight management. Ignoring sleep, and its requirement for daily routine, is ignoring your health, and inviting stress and potentially illness into your life.

Picture showing how the sun raises cortisol levels while the darkness raises melatonin levels
Morning sunlight gently awakens cortisol levels, while darkness raises our Melatonin levels allowing good quality sleep.

Menstrual Cycle Signs


Additionally, if you have menstrual cycles that are longer than 32 days apart from each other, have facial hair, it could be 'stress induced' polycystic ovarian syndrome (PCOS). Perhaps you are an intense exerciser. The same may be true. Stress is another cause of the syndrome. The female reproductive system also follows the same axis pathway, with the ovaries being acted on instead - HPO (Hypothalamic-Pituitary-Ovarian). Stress can effectively halt the ovarian function so menstrual cycles can cease or become irregular. Stress is no joke!

Pathways shown to obesity, mental health issues, and sleep issues that result from chronic stress
How obesity, mental health issues and sleep issues can arise from stress.

Liver Function Importance


Cortisol is also metabolised and cleared via the liver so we need good liver function to eliminate it once it's no longer needed.


If you are someone who ignores chronic stress then you may end up with digestion issues, reproductive issues, blood glucose issues, get sick more often, have obesity issues, insulin resistance, and mental health issues. You may already be experiencing symptoms.


Should you wish to discuss your personal circumstances and seek assistance in these matters with me, please feel free to make an appointment.


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