What does Cortisol Do? | 4 Functions of Cortisol Hormone

Sep 16, 2022

Edited by: Danielle Abel

How does cortisol affect the body?

Cortisol often gets a bad rap because it's known as the "stress hormone," but you actually need cortisol to maintain blood glucose levels. 

The key concept, as with most things, is that it's dose-dependent. Too much cortisol is not good, and neither is too little cortisol. 

You need cortisol to:

  • Break down protein (protein catabolism)
  • Create new glucose (gluconeogenesis)
  • Break down fat (lipolysis)
  • Suppress your immune system (immunosuppression)

Cortisol can help fuel you during a tough workout or help you to keep going on a mentally demanding task. However, if cortisol levels are too high consistently, the hormone has the opposite effect - mobilizing too many fuels and causing too much breakdown that the body can't keep up with repairing. 

Protein Catabolism

Cortisol promotes the breakdown of protein in the body to be converted into glucose through the process of gluconeogenesis. Essentially cortisol is the messenger hormone that signals the initiation of this process. Proteins are broken down into polypeptides which are further broken down into amino acids to be used in gluconeogenesis (below). 


When carbohydrates or stored glycogen isn't available, other substrates can be used to provide the body with energy. Cortisol also stimulates the creation of new glucose from other substrates. The process of creating new glucose is called gluconeogenesis. Protein, lactate, and glycerol can all be used to create new glucose to fuel energy needs in the body. 


Cortisol also promotes the breakdown of fatty acids from stored fat within the body and, to some degree, protects lean muscle mass by mobilizing other types of fuel sources. Lipolysis is the process of removing fatty acid chains from the glycerol backbone where they attach to the molecule. Then, beta-oxidation occurs in which these fatty acid chains are converted into acetyl CoA and can enter the Kreb's cycle for energy metabolism. 


When cortisol is high, your brain is essentially reverting to evolutionary mechanisms that would have been protective of you when danger and concerns for safety were prevalent (getting chased by a sabertooth tiger for example). Luckily we don't have to worry about that anymore, but your subconscious brain doesn't know this.

During times of fight or flight, your immune system isn't the priority, so cortisol actually reduces immune system activation. With this being said, this is why you've probably heard that after a tough workout you're actually slightly immunocompromised. 

Keep in mind that cortisol has a job to do. If you understand its main role in the body (providing glucose to muscles & the brain), then you can better manage it to promote optimal body composition and performance progress. 

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