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Cortisol and Cognition: How the stress hormone affects the brain

Physiologist Aaron Tribby Aviv Clinics by Aaron Tribby, MS , Physiologist
August 23, 2021

If you have heard of the stress hormone cortisol, it certainly has a negative connotation. Stress is bad, right?

High chronic stress and cortisol can negatively harm the body. You may notice changes in cognition–whether it is attentional challenges, slowed processing, poor memory, word recall, or simply muddy thinking. Stress may make those tasks more difficult.

The key word here is may.

Stress does not inevitably lead to brain fog or cognitive impairment.

Many variables, such as environmental factors, type of situations, and the severity, affects the way your body regulates and releases cortisol.

The type of stressors dictates how you as an individual respond to them.

We evolved to adapt to stress

The brain is a problem-solving, learning machine. If it ever encountered anything novel or challenging, it would not learn and acquire new information. And all “stress” really is–a challenge to our system. Everything you do is “stressing” your system.

Stress itself is not inherently a bad thing. Our ability to learn, grow, and thrive is dependent on stress. For example, the body is made to exercise, and muscle needs physical stress to grow big and strong. We adapt and grow as individuals physically, psychologically, emotionally, and even socially.

In fact, if we don’t get stressed out enough as babies and toddlers, we can actually develop a maladaptive stress response. Studies have shown that babies who experienced “infrequent” stressors compared to “moderate” stressors developed an overactive stress response.

It’s been well documented that stress, in small amounts, is beneficial. The classic example is exam anxiety–without some stress, you may not prepare for the test. However, prolonged and/or severe stress can result in the sustained or repeated release of the hormone cortisol. However, technological and societal advancement has far outpaced the evolution of the human brain, and the consequences can be dire to your health.

Biology of cortisol

Cortisol has many jobs in the body, including regulating metabolism and blood sugar, mediating immune function, and coordinating the stress response.

Cortisol is a steroid hormone, a classification of a variety of different molecules that all act as chemical messengers: their job is to relay instructions from one part of the body to the next. But before you dismiss them as “just the messenger,” understand that the messages they deliver are often critical, and almost inevitably set off a chain of biochemical events, depending on the “content” of the message.

In the case of cortisol, that could be almost anywhere. Nearly every cell in your body has been found to contain cortisol receptors, from your heart to your gut to your brain. Bone formation, immune response, electrolyte balance, gut function, and circadian rhythm are all partially mediated via cortisol.

Cortisol and stress

Limbic System Brain Function

One critical job that cortisol does is coordinating the physiological stress response. Your body has a system for this, called the hypothalamic-pituitary-adrenocortical (HPA) axis, and regulating cortisol is its primary job.

The HPA axis uses two different parts of the autonomic nervous system:

  • Sympathetic nervous system for when a threat is detected — the “flight or fight” response.
  • Parasympathetic nervous system (PNS) to calm down the system after the threat is gone — the “rest and digest” system.

So imagine a bear jumps out in front of you–what happens in your body? As the threat is registered in your brain, a small brain area called the hypothalamus sends out chemical messengers to the pituitary gland. It in turn sends out a different set of hormones to the adrenal glands, positioned atop your kidneys. These glands release cortisol.

From there, cortisol rushes to coordinate the physical response: it increases heart rate and respiration, it even narrows your sensory perception, tuning out distractions, all in anticipation to, if you’re using your prefrontal cortex, avoid eye contact and back away slowly.

Do cortisol levels correlate with stress?

Although the association between stress and cortisol is certainly there, research has made one thing clear: the stress response is extremely variable and difficult to correlate with specific metrics.

Researchers have yet to identify a single biological indicator that indicates that a person is “under stress.” There are many hallmarks of the stress response, such as blood pressure and heart rate, and respiratory rate. However, these aren’t reliably caused by stress alone, so other variables can’t be eliminated.

Although it would be convenient if our bodies always responded in exactly the same way, the fact is the situation is highly complex.

There are different types and severity of stressors. The environment makes a difference. Consequences or costs of various responses matter. And perhaps most of all, individual responses vary considerably depending on their development, beliefs, and predisposition.

Normal cortisol fluctuations

Cortisol levels rise and fall in the body according to a 24-hour cycle following our circadian rhythm. At midnight, levels of cortisol are very low if detectable at all. Cortisol then slowly builds up during the night, highest after waking and declining steadily throughout the day.

According to the University of Rochester Medical Center, the normal range for blood cortisol levels from 6:00 am – 8:00 is between 10-20 mcg/dL, and levels off around 4:00 pm to 3-10 mcg/dL.

What causes abnormal cortisol levels? There are many causes, including:

  • Long-term use of corticosteroid medications
  • Autoimmune disorders
  • Inflammation
  • Physical trauma
  • Stress
  • Pregnancy (third trimester)
  • Shift work
  • Depression
  • Alcoholism
  • Malnutrition

How stress affects the brain

Although it is challenging to measure cortisol and correlate it with specific outcomes, there are a few ways cortisol affects the brain.

In general, healthier people had lower levels of overall cortisol throughout the day. In less healthy people, there is a difference in the daily cortisol curve: the lows are higher and the highs are lower. Although the peaks are lower, people showing this pattern released more total cortisol compared to healthier subjects.

The effects of stress on cognition include functional atrophy of the HPA, hippocampus, amygdala, and the frontal lobe in the brain. Functional atrophy means that the brain is losing neurons and functional connectivity.

Chronically high cortisol levels have also been linked to reduced hippocampal volume, a feature also commonly seen in depressed people.

If you have ever felt like stress affects the way you think, below are just a few consequences of high cortisol on the brain:

  • The amygdala, hippocampus, and prefrontal cortex are the most affected areas of the brain. Together, they control emotions, learning, memory, executive function, and decision-making;
  • Mild cognitive impairment (MCI), which is sometimes a precursor to dementia or Alzheimer’s disease, is associated with the hippocampus and elevated cortisol levels;
  • Over-exposure to cortisol can kill off brain cells. The volume of the hippocampus is also lower for people with chronic stress, elevated cortisol levels, and depression;
  • HPA activity has been linked to a more rapid decline in patients with Alzheimer’s disease;

Learning to control how we cope

Removing all stressors is impossible. What matters is how quickly and thoroughly you respond to the situation, and how quickly you return to baseline.

The goal in facing the stressor is to learn how to process and respond to the situation. The body needs to “work,” which requires energy and discipline. For example, when the body is backing away from a wild animal, lots of processes are taking place and energy is being spent. That is being human, and it keeps us alive. Coping mechanisms allow us to adapt for next time.

A failure to cope though is an experience that can be worsened by fear, uncertainty, lack of social support and poor self‐esteem. This is “toxic stress” and makes us more vulnerable to mood and anxiety disorders.

What helps?

Cortisol and Brain Health

“Reduce your stress” is a phrase commonly used by doctors, therapists, even friends. Amid the current uncertainty, you might wonder… How, exactly?

Life is unpredictable and stress is inevitable (not always a bad thing!).

Remember that how you respond to stress matters. Although your response may be ingrained, it’s not hardwired. You can learn to respond better to stress and potentially lower your risk for stress-related diseases.

There are many ways to take control over cortisol and stress. Find what works for you.

  • Move! Studies show exercise improve hormonal function and your stress response;
  • If you are sitting for prolonged periods, get up every hour at least for 5 minutes– many fitness watches have this reminder;
  • Get enough sleep – at least 8 hours every night. Cortisol is regulated by growth hormone, which is secreted certain times at night;
  • Learn to use stress to your advantage: stress inoculation has been shown to improve PTSD symptoms.

Bottom line

Stress and the cortisol hormone are not inherently bad, but an inability to cope with them can lead to a variety of physical and mental health issues. Understand your stressors and find healthy coping mechanisms.

Tip: Interested in learning more about the impact of stress on your body? Check out the close connection between your gut and the brain.

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