The Effects of Cortisol on Blood Sugar and Insulin Resistance

5 minutes read

Cortisol, also known as the “stress hormone,” is essential for your survival — but too much of it for too long can quickly break down your body’s ability to regulate glucose levels and lead to metabolic dysfunction. Learn all about this hormone and its relationship with insulin, plus ways you can manage your cortisol levels for less stress and better glucose control.

What is cortisol and how does it function in the body?

Cortisol is one of the key hormones — along with adrenaline — that your adrenal glands produce when your body is under stress. Together, these two hormones play a crucial role in a tightly orchestrated sequence of events in your body that we call our “fight-or-flight response.”

For thousands of years, cortisol helped our ancient hunter-gatherer ancestors survive in life-threatening situations — like escaping from a predator. In an event like this, the amygdala (the part of your brain that detects threats and manages fear) and hypothalamus (the operator of your brain) sound the alarm bells and send messages through your nervous system to trigger the release of cortisol and adrenaline into your bloodstream.

Some incredible things then happen in a matter of seconds [1]:

your liver releases glucose from its storehouse so you have a surge of immediate energy
your heart rate increases to pump more blood to various organs
your vision sharpens
the airways in your lungs widen to send more oxygen to the brain
anything that isn’t directly related to your survival (like digestion) slows down

If adrenaline is like slamming your foot on the gas pedal, cortisol is like a gentler version of that, where you’re still pressing down but not as hard [2].

Adrenaline is a short-term hormone meant to get you out of an emergency in lightning speed, whereas cortisol is a longer-term hormone that kicks in if the perceived threat hasn’t completely gone away — allowing you to stay alert for more danger.

chart showing mechanisms of how cortisol affects insulin resistance

How does cortisol affect blood sugar and insulin resistance?

One of cortisol’s key jobs is to make sure your body has enough energy to get through a stressful event. It does this by prompting the liver to release glycogen into your bloodstream, which gets converted into glucose, your body’s preferred energy source. Glycogen is the stored form of glucose — any extra glucose from the food you eat that doesn’t get used ends up in the liver as glycogen that your body relies on during fasting, sleep, and situations where you need a quick boost.

In other words, cortisol makes your blood glucose levels go up so you have immediate fight-or-flight energy.

This works in direct opposition to another important hormone in your body, insulin. Insulin’s job is to unlock your cells so that glucose can enter and get transformed into ATP (energy). Insulin also works to store glucose in your liver for later use. When your blood glucose levels rise due to cortisol, your pancreas produces more insulin to try to bring those levels back to normal.

Cortisol and growth hormone (which also gets released during a stressful event) intentionally make your muscle and fat tissue less insulin sensitive to allow you to use up all the circulating glucose in your bloodstream for immediate energy, rather than saving it as glycogen [3].

This is completely fine in the short-term, i.e., in an instance of acute stress. In these moments, your body is well-equipped to handle elevated cortisol and insulin levels temporarily. But the problems start to pile up when you experience repeated instances of stress, or stress that doesn’t go away — also known as chronic stress.

In today’s world, most of us don’t experience the same kinds (or levels) of stress that our ancestors faced. Instead of predators, our struggles often have to do with a challenging job, difficult relationships, debt, moving, illness, and other things that may persist for longer periods of time. You may experience many of these things at once — all of which feel urgent and trigger a stress response — and can leave you in a constant state of elevated cortisol levels.

What happens when your cortisol levels are too high?

Researchers have found that too much stress (i.e., prolonged high cortisol in the body) can negatively affect insulin sensitivity and glucose regulation via several key pathways:

It promotes beta cell death in non-diabetics (beta cells produce insulin), which reduces insulin sensitivity and disrupts glucose regulation.
It weakens lipid metabolism (a classic symptom of diabetes), which is closely associated with insulin resistance.
It can lead to hyperglycemia (high blood sugar levels). Hyperglycemia can trigger chronic inflammation, which is linked to weakened blood vessels, cardiovascular disease, obesity, diabetes, dementia, and other serious diseases and illnesses [4].
It can trigger overeating, especially of processed (high-sugar, high-fat) foods — which can wreak havoc on your glucose levels and lead to big spikes and dips [5]. Studies also show that eating sugary things while stressed can actually dysregulate your cortisol response and make it harder for your body to handle stress [6].
It can disrupt your sleep, which is linked to reduced insulin sensitivity.

Too much cortisol for an extended period of time can start to weaken your cells’ response to insulin and break down your body’s ability to regulate your blood glucose levels — which sets you up for metabolic disaster.

What happens if your cortisol levels are too low?

While high levels of cortisol can be a problem for your health, low cortisol levels aren’t a good thing either. Addison’s disease, also known as adrenal insufficiency, is a rare condition where your adrenal glands don’t make enough cortisol [7]. The symptoms, which include extreme fatigue, darkened skin patches, muscle and joint pain, low blood pressure, and hypoglycemia, can culminate in an “addisonian crisis,” or acute adrenal failure, which can throw your body into a state of fatal shock.

This may sound alarming, but Addison’s disease is extremely rare — only 1 in 100,000 people (or 100 per 1,000,000) have the illness [8]. You’ll need to get a combination of tests — including a blood test, CT scan, insulin-induced hypoglycemia test, and an ACTH (adrenocorticotropic hormone) stimulation test — at a doctor’s office for diagnosis [9].

Addison’s disease also shouldn’t be confused with “adrenal fatigue,” which is based on the idea that too much stress can “burn out” your adrenals so they stop working. You may hear lots of wellness gurus and influencers talk about adrenal fatigue, but it’s 100% a myth that scientists have debunked in multiple peer-reviewed studies [10].

Key takeaways: testing and managing your cortisol levels

Again, cortisol isn’t a bad thing, but it’s meant to be a temporary response. When it becomes unmanageable and chronic, the very mechanisms it triggers for our survival start to break down.

In the 21st century, feeling overwhelmed is often accepted as an unavoidable reality. While it’s not always possible to completely remove yourself from stressful situations, research suggests that some techniques can actually help regulate cortisol levels. So the next time you’re feeling stressed, try:

Deep breathing and breathwork. A 2023 study found that just 5 minutes daily of cyclic sighing (two sharp inhales through the nose followed by a long exhale through the mouth) can help slow your heart rate and relieve stress [11].
Exercising. Just 10 minutes of walking can help improve your mood, lower cortisol levels, and lower blood pressure (which in turn can reduce blood glucose levels) [12].
Calling or texting a friend. Check in with a close friend or family member — research has found that having some kind of reliable support system or community is a key part of building resilience to stress [13].
Spending time in nature. Going for a quick walk in a green space can lower cortisol levels, help you relax, and improve your mood [14].

References:

Written by: James Han

Reviewed by: Emily Johnson, MSc RD

Table of Contents

What is cortisol and how does it function in the body?
How does cortisol affect blood sugar and insulin resistance?
What happens when your cortisol levels are too high?
What happens if your cortisol levels are too low?
Key takeaways: testing and managing your cortisol levels

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