Cortisol and Cognition: How the stress hormone affects the brain

If you have heard of the stress hormone cortisol, it certainly has a negative connotation. Stress is bad, right? So how do the effects of stress on the brain work?

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 muddled thinking. These shifts may make tasks more difficult than they should be.

The key word here is may.

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

Rather, many variables—such as environmental factors, type of situations, and stress severity—affect how 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

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 the muscles need physical stress to grow big and strong. We adapt and grow as individuals physically, psychologically, emotionally, and socially.

In fact, if we don’t get stressed out enough as babies and toddlers, we can actually develop a maladaptive stress response. Studies show 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. However, prolonged and/or severe stress can result in the sustained or repeated release of the hormone cortisol. The classic example is exam anxiety—without some stress, you may not prepare for the test. 

What Is Cortisol and Its Relationship to Stress?

Cortisol coordinates the physiological stress response. The body releases cortisol when you experience any type of stress (i.e. acute, chronic, and traumatic stress) via the hypothalamic-pituitary-adrenocortical (HPA) axis.

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—the small endocrine gland at the base of your brain.
  
• Cortisol rushes to coordinate the physical response. It increases heart rate and respiration, narrows your sensory perception, and tunes out distractions—all in anticipation to avoid eye contact with the bear and back away slowly.
• The pituitary gland then sends out a different set of hormones to the adrenal glands, positioned atop your kidneys. These adrenal glands release cortisol.

What Is the Biological Significance of Cortisol?

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

Cortisol’s 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 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.

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. Thus, their association is difficult to connect with specific metrics.

Researchers have yet to identify a single biological indicator that conveys a person is under stress. There are many hallmarks of the stress response, such as blood pressure, 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.

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.

How Do Cortisol Levels Fluctuate?

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 Does Stress Affect the Brain?

The effects of stress on the brain include functional atrophy of the HPA, hippocampus, amygdala, and the frontal lobe. 

Functional atrophy means that the brain is losing neurons and connectivity between those neurons. This can impair brain functions such as thought processing, memory, and emotional regulation. 

In general: 

• Healthier people have lower levels of overall cortisol throughout the day. Cortisol levels are typically highest in the morning and lowest at midnight. 
• 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.

What Are the Long-Term Cortisol Effects?

Research indicates long-term high cortisol levels are linked to reduced hippocampal volume—a feature also common in depressed people.

If you have ever felt like stress affects the way you think, below are just a few consequences of high cortisol levels 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 hippocampus volume 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.

How Can You Cope with Stress? 

“Reduce your stress” is a phrase commonly used by doctors, therapists, and 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 improves 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: Sleep at least 8 hours every night. Cortisol is regulated by growth hormone, which is secreted at certain times at night.

• Use stress to your advantage: Stress inoculation has been shown to improve PTSD symptoms.

The Bottom Line

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

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