The most important cortisol function is to respond to stress appropriately. We tend to think of stress as a bad thing we need to avoid.
Stress however can mean a physical threat to our bodies like an infection or even normal physical exertion like getting out of bed in the morning. In fact, cortisol is generally higher in the morning and gradually drops lower later in the evening as melatonin rises to make us sleepy. Many women with Chronic Fatigue Syndrome show low or flat levels of cortisol, particularly in the morning. Low cortisol makes everything difficult.
Adrenaline and Cortisol
Adrenaline is the fight / flight hormone released immediately by the adrenal glands. This response mobilizes huge amounts of energy Cortisol works with adrenaline, is slower acting and helps the body recover from this initial rush. Cortisol release stored sugar and fatto refueling the heart, lungs, and legs.
Insulin and Cortisol
Insulin is the fat storing hormone (anabolic). Cortisol triggers insulin by increasing blood sugar, but shuts down its storage effects. This is how chronic stress can increase insulin resistance – blood sugar and insulin spiral upwards. It signals fat cells to hold on to their stores
Main Cortisol Functions
In evolutionary terms, what would be a useful response to stress or threat? If you were designing a being, the following cortisol functions would make sense to include:
- To increase blood sugar levels for energy to be able to deal with the stress. You may need energy to fight an illness for instance or deal with a threat, or to refuel. This can create havoc with diabetes management and insulin resistance problems.
- To increase in blood pressure to provide strength. The heart works harder to provide blood to legs for running and arms for fighting for instance.
- To decrease inflammation and suppress the immune system. Inflammation and fighting infection uses energy and slows blood flow. These activities might divert resources from the task of dealing with the stressor. The internal fighting might compete with the external fighting. The anti-inflammatory benefits are behind synthetic cortisone’s popularity.
- To decrease fertility and testosterone. In chronically stressful situations such as famine, the last thing humans would need is more mouths to feed. When you need to focus on the two Fs (fighting and fleeing), the third F is irrelevant.
- To decrease serotonin. Excess serotonin can result in loss of motivation and drive. Contentment is the last thing you would need. Decreasing serotonin can lead to depression, but also cravings for sugar and/or refined carbohydrates.
- To decrease sensitivity to pain in order to focus on the task. Not useful to notice how much the splinter in your finger hurts.
- Heightened memory – in stressful situations, it is useful to be more alert. Remembering the circumstances that led to the threat can prevent future problems. In the long term, thinking becomes foggy however.
As you can see, cortisol is a vital hormone and having low levels of it can create major difficulties. Anyone suffering from adrenal burnout would understand how hard it makes even simple tasks. On the other hand, chronic stress and high overall levels of cortisol can cause major health problems. High blood pressure increases the risk of strokes, high blood sugar and insulin resistance increases the risk of type 2 diabetes. A permanently suppressed immune system can open you up to infections and cancers. Low testosterone and serotonin can make you fat, depressed and/or cranky.