Cortisol is a steroid hormone made from cholesterol in the two adrenal glands above each kidney. It is best known for its role in the ‘fight or flight’ response and how, in stressful situations, it can increase the body’s energy production temporarily.
The secretion of cortisol is controlled by the hypothalamus, the pituitary gland and the adrenal gland . When there are low cortisol levels in the blood, the hypothalamus releases corticotrophin-releasing hormone, which then stimulates the release of adrenocorticotropic hormone by the pituitary gland into the bloodstream; high levels of this hormone cause the adrenal glands to secrete cortisol. The cortisol levels rise and block the release of the corticotrophin-releasing hormone from the hypothalamus and therefore the adrenocorticotropic hormone from the pituitary . This leads to the adrenocorticotropic hormone levels dropping which then reduces the cortisol levels; it’s a negative feedback loop.
In stressful situations, cortisol releases glucose by the gluconeogenesis from protein stores in the liver . If cortisol levels don’t return to normal, remaining high then glucose is consistently released resulting in high blood sugar levels. This means that insulin, which is released to reduce blood sugar levels is ‘overruled’ by the high cortisol levels that continue to release glucose; the body becomes resistant to insulin but the demand for insulin remains high. The pancreas can’t keep up with the demand of insulin and so the glucose levels in the blood remain high but because the cells have become insulin resistant anyway they’re not able to absorb the glucose that they need for respiration.
Cortisol regulates energy by choosing which and how much of a certain substrate- carbohydrates, proteins or fats- to meet the needs of the body. This explains why, when cortisol levels remain high in the blood instead of returning to normal can lead to weight gain and obesity. Cortisol can take triglycerides from storage and move them to visceral fat cells which have more cortisol receptors than the fat under layers of skin (subcutaneous) inside the abdomen . Also, due to the blood glucose level problem explained above, if the cells aren’t getting enough glucose, messages are sent to the brain to fix the problem; the individual eats. This can lead to overeating and the excess glucose is just stored as fat. Cortisol has also been found to encourage craving for high calorie foods, which I’d imagine would have the most glucose to be absorbed by the cells that are struggling to absorb glucose, by binding to the hypothalamus.
High levels of stress and other factors like a poor diet can lead to chronic inflammation that keeps cortisol levels high  and suppresses the immune system over time. This leads to an increase in the risk of getting ‘common’ illnesses like colds but also more serious diseases like cancers and even food allergies because of how weak the immune system is. A weak immune system can lead to autoimmune diseases and because the immune system determines how healthy the small intestine is, the individual is more susceptible to gastrointestinal issues like constipation.
Cortisol also constricts the blood vessels to increase the delivery of oxygenated blood, which is great for ‘fight or flight’, but leads to a high blood pressure overtime, increasing the risk of cardiovascular disease. Even erectile dysfunction, ovulation, and menstruation can be disrupted by high levels of cortisol  , also if cortisol is being produced in high levels, the sex hormones that are produced in the same place are placed on the ‘back burner’.
So how can we manage our stress to avoid these problems? Source  recommends an anti-inflammatory diet and stress management to control the levels of cortisol in the blood.
Today, I’ve focused mainly in what happens when the cortisol levels are too high but the everyday role of the hormone throughout the organ systems is vital to survival. Thanks for reading!
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