The Absolute Lowdown On Cortisol – Body’s Key Hormone

The Absolute Lowdown On Cortisol - Body's Key Hormone
The Absolute Lowdown On Cortisol - Body's Key Hormone

Most of us associate too much cortisol with the loss of muscle and gain of more belly fat, something that I am pretty confident that most of us are actively trying to avoid! But too little cortisol leaves us feeling “chronically fatigued.” Neither of which are very appealing, and that’s just the tip of the iceberg. Let’s talk about some cortisol basics and then briefly discuss what can go wrong when our levels aren’t optimal.

What is Cortisol?

Cortisol is a glucocorticoid, also known as hydrocortisone. It’s produced in the adrenal cortex in response to stress (physical or emotional) and according to natural cycles that tend to correlate to circadian rhythms. It is made from cholesterol and its synthesis and release is controlled by adrenocorticotropic hormone (ACTH). Cortisol helps us get our butts out of bed in the morning and function day to day. In the morning, cortisol rises until it peaks around 8:00am. This helps us feel bright-eyed and bushy-tailed. As the day wears on, it falls gradually, reaching its lowest levels around 3:00-4:00am.


Role of Cortisol

Cortisol plays a big role is the body’s stress response. It helps us deal with stress by shutting down unnecessary functions, like reproduction and the immune system, in order to allow the body to direct all energies toward dealing with the stress at hand. These functions of cortisol are supposed to be short-lived, just long enough to deal with the offending stressor. However, our modern lives are anything but stress free and when stress is chronic this becomes a problem.

How exactly does cortisol affect the body during times of stress?

Cortisol stimulates gluconeogenesis (the making of new glucose) in the liver, using amino acids, lactate, glycerol, and propionate. It is also involved in glycogenolysis (the breakdown of glycogen stored in the liver and muscle cells), which is necessary as it activates glycogen phosphorylase, an enzyme needed to complete the whole process. Cortisol also inhibits insulin from shuttling glucose into cells by decreasing the translocation of glucose transporters to the cell surface. All of this results in quite a bit of glucose floating around in the blood stream. This is great if we’re actually running to save our live – However not so good if you’re just stressed about paying your bills.


Effects of Cortisol

Cortisol also partially shuts down the immune system when levels are high. It interferes with T-cell production and function, making your body more susceptible to invading pathogens. Ever notice how people who are constantly stressed are always getting sick? Or how a person can go through a major stressor and right after overcoming it become incredibly ill? We usually chalk this up to bad luck, but is it really luck or is it a body too overwhelmed to cope anymore?

Bones and muscles are also affected by cortisol. It inhibits the uptake of amino acids into the muscle cells, making it damn near impossible to fuel muscle cells when cortisol levels are too high for too long. It also inhibits bone formation and decreases calcium absorption in the intestine. So, when cortisol is high, there’s no bone growth and no muscle growth. This could be problematic.


Our blood pressure also goes up in the presence of elevated cortisol levels. This is due to several different mechanisms. Cortisol makes the body more sensitive to the effects of epinephrine and norepinephrine, causing vasoconstriction, or reduced blood flow, in many parts of the body. It also serves as an anti-diuretic and causes the body to retain sodium. Again, this is great if we actually need to perform a physical task. However, if we’re under constant stress, high blood pressure, decreased blood flow to some of our organs, and sodium and water retention are not really signs of great health.

What does cortisol do in our body?

Let’s name a few more things that cortisol does in the body. Keep in mind these things are beneficial in the short term, but problematic if cortisol stays elevated for long periods of time:


– Cortisol production, both too little and too much, can interfere with the production of thyroid hormones and the conversion of T4 to T3.

– It causes an increase in gastric acid production. When chronic, this can lead to reflux and other problems in the intestine. The decreased blood flow to the GI tract can also cause incredible problems with digestion.


– It disrupts the reproductive system, causing infertility or even miscarriage when cortisol levels are too high or chronically elevated.

– When our reproductive system shuts down, guess what hormone level goes down? Testosterone. I shouldn’t have to explain why that can cause some pretty negative things to happen in regard to your training and fitness goals.


– It decreases inflammation by reducing the secretion of histamine and stabilizing cellular structure.

– Increasing cortisol and chronically elevated cortisol can cause intense hunger and food cravings due to the metabolic derangement that occurs. Okay, if you just fought off a lion. Not okay if you sat in the car for an hour during rush hour traffic.


How does cortisol production become deranged?

Normally when cortisol reaches a certain level it automatically shuts off the mechanisms that signal for it, therefore limiting production. It goes something like this:

The hypothalamus, when it senses a stressor, produces CRH (corticotropin releasing hormone), which then stimulates the anterior pituitary gland to produce ACTH, which then stimulates the adrenal gland to produce cortisol. When cortisol levels get high the message is sent to the hypothalamus and the anterior pituitary that, “Hey guys, we’re backed up here. Time to shut it down for a while.”

Now, it is thought that when cortisol levels are too high for too long this feedback mechanism gets a little screwy. I like to think of it like insulin resistance. If we pound cupcakes and candy day in and day out for too long we become insulin resistant and we then need medicine, or a major diet overhaul, to get our blood glucose under control. The same seems to apply to cortisol and adrenal health. We let stress get the best of us for too long and our bodies just can’t handle it anymore. Cortisol production may go through the roof, your body may not make enough, or you may make a ton of it at night when you’re trying to sleep and nothing in the morning. Ugh.

As you can see, cortisol and the adrenal system are finicky and complex. Without cortisol, our bodies cannot deal with the stress we encounter on an everyday basis. However, when we abuse our minds and our bodies, we eventually pay the price. Our cortisol levels become incongruent with our needs. Think about this the next time you “suck it up” and go to the gym on four hours of sleep or say yes to yet another work project that you may or may not actually have time to complete. While some part of you might be proud for toughing out the workout today, are you actually negatively impacting your health and fitness goals?


1. The Institute of Functional Medicine, Textbook of Functional Medicine, (Gig Harbor, WA: 2010)