What is cortisol (and what does it do)?

Cortisol (often called your stress hormone) is a steroid hormone. It regulates various processes in your body, including your stress response, immune response and metabolism. The following article will explain the role of cortisol in your body - particularly its role in your stress response.

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The role of cortisol in your body

As we mentioned above, cortisol is a steroid hormone which is often linked to our body's stress response. Understanding how your body's stress response works is the first step towards successful stress management.

Your cortisol secretion is regulated by your hypothalamus (your brain's command centre), your pituitary gland and your adrenal gland. This combination of glands is called your HPA axis. Although cortisol is most well known for its role as the primary stress hormone, cortisol has several other pretty important functions. Almost every cell in your body contains cortisol receptors. 

What does cortisol do?

  • Controls your blood sugar levels
  • Regulates your metabolism
  • Reduces inflammation
  • Improves memory formation
  • Controls salt and water balance 
  • Regulates blood pressure
  • Assists with foetal development
  • Triggers vital processes involved in giving birth
  • Primary hormone involved in your body's stress response

The below diagram depicts the chemical structure of cortisol:

Scientific illustration of cortisol

The role of cortisol in your stress response

As we mentioned earlier, cortisol is the primary hormone involved in your stress response (hence being called "the stress hormone"). In order to explain where cortisol fits in, let's take a quick look at how our bodies' stress response actually works.

How your body responds to stress

Your body responds to stress instinctively - whether you're being chased by a lion or hear a balloon pop, you're hard-wired to survive.

Your body enters fight or flight mode when it is stressed | DNAFit Advice Centre
When you encounter a perceived threat, your body prepares for "fight or flight"

Your amygdala (the emotional processor in your brain) sends an emergency distress signal to your hypothalamus. Your hypothalamus then communicates with your body through the Autonomic Nervous System (ANS), enabling you to either confront the threat (fight) or avoid the threat (flight). 

Your ANS regulates your basic bodily functions. It operates instinctively, with its primary goal being to keep you in a safe state of physiological balance.

There are two components to your ANS, the sympathetic and parasympathetic systems. The sympathetic system is the fight or flight division - it stimulates you to take action. Your parasympathetic system is the rest and digest division, which is responsible for calming and relaxing your body.

When your hypothalamus triggers your body's alarm system, you releases a surge of stress hormones - including adrenaline and cortisol. 

What is adrenaline and what does it do?

Adrenaline is a hormone which prepares your body for fight or flight. It increases your blood circulation, heart rate and breathing rate. Adrenaline also increases your carbohydrate metabolism. It suppresses your appetite, sending blood away from your organs to your muscles - preparing them for exertion.

Once the perceived “threat” has passed, cortisol alerts your body to replenish energy. This causes us to crave snacks with a high sugar and fat content - which is why our knee-jerk reaction is to reach for that doughnut. 


In comparison, worrying about work or traffic doesn’t burn off nearly as much energy. Unfortunately, our bodies don’t know the difference when it comes to dealing with a stressor. Our hormones still react the same way to stress as our ancestors’ hormones did throughout history.

The effects of chronic stress on your cortisol levels

Chronic stress leads to higher levels of cortisol in your system, for a prolonged period of time. This can affect weight gain as it causes you to not only eat more than usual, but to eat the wrong foods. Cortisol, as we explained above, slows down your metabolism, reserving and replenishing energy.

The symptoms of high cortisol levels

High cortisol levels can lead to the following health conditions:

  • Weight gain (especially belly fat)
  • High blood pressure
  • Muscle weakness
  • Fatigue
  • Weak immune system
  • Difficulty healing wounds
  • Thinning skin, easy bruising and flushed face 
  • Headaches
  • Irritability
  • Difficulty concentrating

The symptoms of low cortisol levels

Low cortisol levels can be equally damaging to your health. Symptoms include:

  • Weight loss and decreased appetite
  • Fatigue
  • Muscle or joint pain
  • Low blood pressure that could lead to fainting spells
  • Low blood sugar
  • Nausea and vomiting
  • Diarrhea
  • Hyperpigmentation (darkening of the skin)
  • Irritability
  • Depression
  • Hair loss

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