Cortisol is generally best known as the “stress hormone.” However, it’s truly amazing how an imbalance—either high or low—can set off a cascade of changes in the body that can be difficult to restore back to balance.
What is Cortisol?
Cortisol is a hormone synthesized in the adrenal glands. Cholesterol is the first ingredient in the production of cortisol. Cortisol is released when people experience stress, in order to address the changes that occur in the body .
Cortisol also controls blood sugar levels, fat, protein, and carbohydrate metabolism, immune responses, anti-inflammatory action, blood pressure, heart and blood vessel tone and contraction, and central nervous system activation .
How it Works: A Scenario
A typical scenario would be someone facing a mugger on the street. This causes stress on the individual. The adrenal glands produce cortisol in response to the increased stress levels.
Cortisol fills the blood with glucose to be used by the muscles for energy. Insulin is restricted so glucose can be readily used instead of stored .
Arteries are narrowed to increase blood pressure, and epinephrine increases the heart rate. This makes the heart work harder and lets the individual react quickly to the situation .
The person being mugged will either fight the mugger or run away. Either way, the situation is resolved and cortisol levels should go back to normal. Glucose can be stored once again and insulin is no longer restricted .
Cortisol reduces the impact of stress on the body and returns it back to homeostasis levels .
Cortisol’s Role in Blood Sugar Levels
Cortisol’s anti-insulin effects are there to increase glucose uptake and usage in the brain, heart, and muscles . These are the places that need it most when you’re running from a mugger.
Cortisol increases glucose production and reduces glucose uptake in certain tissues .
Cortisol makes glucose from glycogen (the storage form of glucose) in response to stress. This provides immediate metabolic energy so that the body can function and react to the situation.
Cortisol reduces glucose delivery to some tissues by impairing local blood flow (such as to the stomach and digestive system) while it increases blood flow to the heart and leg muscles .
Cortisol simultaneously stimulates both glucose storage (glycogen synthesis) and glucose breakdown (glycogenolysis) . It depends on other factors like insulin levels.
When there are low insulin and high adrenaline, cortisol may cause a more effective release of fuel and higher glucose output. When there’s high insulin, cortisol may promote glycogen (glucose) accumulation .
Cortisol Affects Electrolytes
Cortisol acts as a diuretic, which leads to water and potassium excretion and sodium retention. It increases potassium excretion in the intestines as well (which might affect the gut flow) .
I ask in my questionnaire whether people urinate frequently to get a pulse on their cortisol (and vasopressin) levels. Some people have reduced cortisol after a long period of chronic stress.
As it is, our modern diets are extremely imbalanced in that we get too much salt and too little potassium. HPA activation by stress can, therefore, worsen this imbalance. Anxiety and its associated increase in various neurotransmitters increases magnesium excretion .
Cortisol also decreases calcium uptake in the kidneys and more of it is released in the urine instead of being utilized, which may cause calcium deficiency and kidney stones. Normally, aldosterone increases calcium reabsorption, but cortisol competes with it .
Cortisol’s Positive Effects
While high levels of this stress hormone are problematic, low levels aren’t good either. Cortisol is absolutely essential for everyday energy and functioning of the body .
Cortisol counteracts stress and increases energy by burning fat for fuel .
Cortisol decreases hypoglycemia (low blood sugar) by increasing blood glucose. When I have a thin client who suffers from hypoglycemia, it suggests that his or her cortisol levels might be chronically or intermittently low. This is one of the main defining features that separate the hypoglycemics from those who don’t get hypoglycemia often .
Cortisol stimulates internal antioxidants such as SOD (Superoxide Dismutase) .
Cortisol stimulates stomach acid secretion, which can help with thorough digestion .
Cortisol’s Negative Effects
1) Weight Gain
Cortisol causes weight gain, on the whole. It is one of the big 4 hormones that help determine weight. Cortisol secretion is elevated in obesity, but blood levels are normal because it gets deactivated. It’s in fat tissue itself that cortisol is elevated .
Cortisol is associated with increased appetite, cravings for sugar, and weight gain in both animal and human studies .
Cortisol seems to directly influence food consumption by binding to receptors in the hypothalamus. This can stimulate an individual to eat food that is high in fat and/or sugar .
Women with a higher cortisol response chose to consume more foods high in sugar and fat .
Cortisol also indirectly influences appetite by regulating other hormones that are released during stress such as CRH, leptin, and NPY (neuropeptide Y) .
Cortisol increases leptin secretion from fat cells .
Cortisol decreases insulin secretion and increases insulin resistance, which will raise insulin levels in the longer term .
Besides leading to diabetes, this also depletes cells of energy and they signal the body to replenish energy stores: “EAT!”
2) Cognitive Impairment
The hippocampus (memory center) contains many cortisol receptors. Excess cortisol overwhelms the hippocampus and actually causes it to decay. Cortisol/Glucocorticoids impair declarative memory retrieval and working memory (WM) performance .
Cortisol stimulates liver detoxification by inducing tryptophan oxygenase, which also has the effect of reducing serotonin levels in the brain .
Cortisol also induces glutamine synthetase, which reduces glutamate levels in the brain (not good if it’s too low or too high) .
Studies of the elderly show that those with elevated cortisol levels display significant memory loss. The damage is usually reversible. Stress also decreases neurogenesis, or the ability to create new neurons, in our memory centers (hippocampus) .
3) Immune System
Since cortisol works to decrease stress-induced inflammation, it also weakens the immune system, which makes people more susceptible to sickness.
Cortisol weakens the activity of the immune system by:
- Inhibiting IL-12, interferon gamma and alpha, TNF and Th1 cells .
- Increasing IL-4, IL-10, and IL-13 by Th2 cells .
- Inhibiting Histamine secretion 
- Reducing production of T-cells by making them unresponsive to IL-1, which lessens IL-2 (a T-cell growth factor) .
- Inhibiting Natural Killer Cells (by inhibition of natural cytotoxicity receptor. Prolactin activates) .
- Inhibiting NFκB .
Cortisol decreases the Th1 response and favors more of a Th2 response. It inhibits IgM and IgA, but not IgE antibodies .
4) Cardiovascular Disease
Because of the increase in blood pressure in constricted vessels, it is possible for cortisol to cause heart attacks. Constant cortisol release damages blood vessels.
Cortisol will cause higher blood pressure by retaining sodium, excreting potassium, and making your blood vessels contract .
In the absence of cortisol, widespread vasodilation (relaxation of blood vessels) occurs .
Cortisol also increases blood pressure by increasing the sensitivity of blood vessels to epinephrine and norepinephrine .
A 2010 study found that blood cortisol predicts increased death from heart disease .
Cortisol reduces bone and collagen formation [23, 24].
It decreases osteoblasts and therefore will lead to decreased bone density (by inhibiting periosteal cells) .
Cortisol also reduces calcium absorption so you will be deficient in calcium .
Indeed, various studies show that higher cortisol is associated with lower bone mineral density in people [27, 28].
6) Sexual Dysfunction
Cortisol levels that are too high can also impede sexual activity. When cortisol is being overproduced, the sex hormones are not being produced in their usual quantities, since they are produced in the same place, the adrenal glands .
Cortisol shuts down the reproductive system, resulting in an increased chance of miscarriage and (in some cases) temporary infertility .
7) Muscle Wasting
In chronic stress, growth hormone is decreased .
Cortisol decreases amino acid uptake by muscles and inhibits protein synthesis. This means we won’t build muscle as well .
Cortisol also breaks down muscle .
Collagen is a molecule that makes connective tissue. It is vital for structural support and is found in muscles, tendons, and joints, as well as throughout the entire body. Cortisol inhibits collagen .
Increases in cortisol have been found to lengthen wound healing time in healthy, male adults .
Those who had the lowest levels of cortisol the day following an injury had the fastest healing time .
Cortisol delays wound healing .
In dental students, wounds (punch biopsies) took an average of 40% longer to heal when performed three days before an examination as opposed to wounds on the same students during summer vacation .
9) Anxiety and Depression
Cortisol activates the “Kynurenine Pathway”, which shunts tryptophan to make a molecule that will cause neuron loss, anxiety and depression (Kynurenine, Quinolinic acid), instead of making serotonin .
High or Low Cortisol Causes
For a more comprehensive list of why cortisol can be too high or too low, check out this post.
Causes of High Cortisol
High cortisol levels can be caused by Cushing’s syndrome, a disorder in which the body has too much cortisol, and Cushing’s can, in turn, be caused by overactive adrenal glands, an adrenal gland tumor, or by steroids.
In Cushing’s syndrome, there is an accumulation of fat in the belly, neck, and cheek, but a decrease of fat in many other places.  There may also be an accumulation of fat in the liver in Cushing’s syndrome .
Cortisol can also be elevated due to liver or kidney disease, obesity, depression, pregnancy, sickness, and injury.
Cortisol can be increased in production by viral infections, caffeine, not sleeping, intense or long aerobic exercise like running or climbing stairs, not eating, low-calorie food, high stress, among other things [36, 37, 38, 39].
Causes of Low Cortisol
Low cortisol can be caused by Addison’s disease, a condition in which the adrenal glands cannot make enough cortisol, or due to problems with the pituitary gland – cortisol’s next stop after being released from the adrenal glands.
PTSD is associated with lower cortisol and higher DHEA .
Circadian rhythm disruption can cause low cortisol. In animals, light at night alters daily patterns of cortisol and clock proteins [41, 42]. In humans, it also alters circadian clocks .
What Increases or Decreases Cortisol?
We’ve put together a few more posts about cortisol, each taking a deep dive into your stress response, what could be raising it, and what could help. Check them out here:
- 58 Ways to Inhibit Your Stress Response and Decrease Cortisol
- 63 Factors Raising Your Stress and Cortisol Level (backed by science)
- Reasons Why Your Cortisol is Low or High: HPA or Stress Response Triggers)