How does stress increase cortisol levels?

Cortisol is widely known as the “stress hormone” and for good reason, as stress triggers a surge in cortisol. Cortisol also influences various other functions throughout the body too.

How are cortisol levels controlled?
Cortisol is a steroid hormone synthesized from cholesterol in the adrenal glands, with secretion controlled by the HPA axis. The HPA axis is a combination of glands that includes the hypothalamus, the pituitary gland, and the adrenal gland. This HPA axis follows a circadian rhythm, which means that cortisol levels are generally higher in the morning and lower at night (1).

When the hypothalamus detects low cortisol, low blood sugar, or times of stress, it releases corticotropin-releasing hormone (CRH), which signals for the pituitary to release adrenocorticotropic hormone (ACTH). ACTH then acts on the adrenal gland to trigger the synthesis and secretion of cortisol. Elevated cortisol levels inhibit the release of CRH and ACTH, providing a negative feedback loop to control cortisol levels (1).

What are the roles of cortisol?
Cortisol mediates the stress response, as well as helping regulate metabolism, the inflammatory response, and immune function. In times of stress, a surge in cortisol helps provide energy to the body by increasing blood sugar through gluconeogenesis (synthesis of ‘new’ glucose). Glucose is especially important as an energy source for the brain, helping to give that extra mental boost, such as when there is an important deadline approaching!

Cortisol is also involved in the metabolism of fat, protein, and carbohydrates. It helps control blood pressure and is even involved in memory formation. In addition, cortisol enhances the activity of epinephrine (adrenalin), which is what causes a faster heart rate and faster breathing in times of stress (1,2).

What happens if cortisol levels stay high for a long time?
Usually, cortisol only remains elevated for a few hours after a stressful event. However, in people who are suffering from chronic (long-term) stress, cortisol levels can remain elevated for several months. These persistently elevated levels of cortisol can increase the risk of various health complications, including anxiety, depression, digestive problems, weight gain, and insomnia (2).

References:
1. Thau L, Gandhi J, Sharma S. (2020). Physiology, Cortisol. [Updated 2020 May 29]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2020 Jan-.
2. What is Cortisol? (Nov 2018). Hormone Health Network, Endocrine Society.