Understanding Your Brain 101: Cortisol and the Stress Response

blog written by Abby Jo Vanderfin, Cal Poly, San Luis Obispo undergraduate intern, supervised by Dr. Hannah Roberts

Why Do You Feel Stressed?

Ever notice how your heart races before a big presentation, or the pressure you feel when you have a deadline creeping up? That’s your brain’s stress response at work. Stress isn’t just a feeling—it’s a biological reaction driven by cortisol, your body’s primary stress hormone. 

We all feel stress in some regard, and unfortunately, chronic stress is not uncommon AT ALL. In fact, the average level of stress Americans report is five out of ten, with a quarter of adults rating their stress between eight and ten (American Psychological Association, 2023). When our stress is too high or persistent, it can change our brain functioning and affect our physical health. Studies have suggested that 60-80% of doctor visits are stress-related (Nerurkar et al., 2015).  

But the good news? Understanding what stress is, what causes it, and how to help your body react to it can help you regain control over your mind and body.

What Is Cortisol?

Cortisol is a hormone produced by your body in response to stress. It plays a crucial role in regulating metabolism, inflammation, and immune function—but its most well-known role is helping the body respond to threats.

 How Cortisol Works in the Brain:

1. When you experience stress, your hypothalamus (the “command center” of your brain), through a chain of events, signals your body to release cortisol. 
2. Cortisol equips your body for danger via the fight or flight response. In an evolutionary context, cortisol would help your body by increasing your heart rate, alertness, and energy which would help you fight or run from a threat. However, our bodies have not caught up to modern society, causing your nervous system to sometimes not be able to tell the difference between speaking in front of an audience and a tiger chasing you in the wild. 
3. Once the stressor is gone, cortisol levels should return to normal (baseline)—allowing your body and mind to relax. 

   But when stress is constant, this system stays activated, keeping cortisol levels chronically high, which can have serious effects on your brain and body. Your body is not meant to always be in a state of fight-or-flight, and thus can have major impacts on your mental and physical health. 

   Is Stress Really Bad?

   However, stress is not your enemy! Stress is your brain and body’s way of trying to keep you safe. Believe it or not, stress can actually be your friend! When faced with a challenge, your body releases cortisol to increase energy, focus, and alertness, helping you rise to the occasion. 

   Your body is not working against you, it’s actually working for you. Your pounding heart is actually preparing you for action. And your increased breathing is actually getting more oxygen to your brain.

   The key is how you perceive stress. Research shows that when people view stress as helpful—like a boost to get through a tough situation—they feel less anxious and perform better. Their blood vessels even stay more relaxed, mimicking the body’s response during moments of joy or excitement (Crum et al., 2013; McGonigal, 2013).

   This means that stress itself isn’t the enemy. It's how you think about it, and not always being in a state of stress that matters. By reframing stress as a tool for growth and resilience, you can transform how it affects your body and mind.

   How Chronic Stress Affects the Brain

   When cortisol remains elevated for long periods, it can affect your brain’s functioning through:

    Memory & Learning: Chronic stress shrinks the hippocampus, the brain’s memory center, making it harder to retain and recall information (McEwen et al., 2016).

   Emotional Regulation: High cortisol over-activates the amygdala (your brain’s fear center), making you more reactive, anxious, or irritable (Kinner et al., 2018). This effect is even more pronounced in heavy drinkers, as chronic alcohol use can dysregulate the HPA axis - the part of your brain that regulates your body’s response to stress. This can lead to higher baseline cortisol levels and an exaggerated response to stress (Karin et al., 2020). Over time, this can make the brain more sensitive to stress triggers, increasing vulnerability to anxiety and depression. 

   Decision-Making: Prolonged stress weakens the prefrontal cortex, which is responsible for rational thinking, focus, and impulse control (Woo et al., 2021). 

   Sleep & Recovery: Excess cortisol disrupts melatonin production, making it harder to fall and stay asleep, leading to brain fog and exhaustion (Hirotsu et al., 2015).

   Bottom Line: Chronic stress can literally change your brain structure and functioning, making it harder to stay calm, think clearly, and feel balanced. But the good news? You can reverse these effects by training your brain to regulate cortisol.

   Chronic Stress and Your Physical Health

   Stress doesn’t just affect your mind—it has real consequences for your body as well. When cortisol stays elevated for long periods, it can contribute to serious health problems, including:

• Heart Disease: Chronic stress increases blood pressure and inflammation, raising the risk of cardiovascular disease (Steptoe & Kivimäki, 2022).
• Weakened Immune System: High cortisol levels suppress immune function, making you more susceptible to colds, infections, and slower wound healing (Glaser & Kiecolt-Glaser, 2018).
• Digestive Issues: Stress disrupts gut function and can worsen conditions like irritable bowel syndrome (IBS) and acid reflux (Chrousos, 2020).
• Weight Gain: Cortisol encourages fat storage—particularly around the abdomen—and can contribute to issues with the metabolism (Adam & Epel, 2021).
• Muscle Tension & Chronic Pain: Stress causes persistent muscle tension, which can lead to headaches, migraines, and musculoskeletal pain (Croff et al., 2019).

How to Reduce Cortisol & Train Your Brain for Resilience

The key to managing stress isn’t eliminating it entirely—it’s teaching yourself and your brain how to handle it better. Here’s how:

1. Shift Your Mindset to Transform Stress

How it works: Your mindset about stress influences how your body reacts to it. Viewing stress as a helpful response to a challenge rather than a threat changes your body’s response, helping you feel more confident and in control. People who adopt this mindset have been shown to have healthier cardiovascular responses in response to stressful tasks, effectively affecting your health long-term (Crum et al., 2013; McGonigal, 2013).

Try this: The next time you feel stressed, remind yourself: “This is my body helping me rise to the challenge.” This simple shift can transform stress into a source of strength, making you more resilient.

2. Help Your Body Return to Baseline with Mindfulness

How it works: Mindfulness trains your brain to better respond to stress. Studies show that meditation may reduce cortisol levels and lower stress levels, making you more resilient to stress (Tang et al., 2015).

Try this: Practice deep breathing or a 2-minute body scan when you feel unnecessarily overwhelmed. 

How to do a body scan:

Find a calm place to sit, lie down, or stand 

Close your eyes 

Take notice of your breath 

Start at the top of your head

Slowly move your awareness down your body, noticing any sensations or feelings. Start with your head, moving down to your shoulders, chest, stomach, and down your limbs all the way to your fingers and toes. 

When you notice tension, focus your attention on it and breathe. With each breath imagine the tension being released.  

When you’re ready, return to your surroundings and open your eyes 

3. Use Movement to Regulate Stress

How it works: Regular exercise is linked to more effective cortisol regulation, meaning that exercise may be effective in maintaining lower overall stress levels (Moyers & Hagger, 2023).

Try this: Even 10 minutes of walking can reduce stress hormones. Yoga, strength training, or dancing are also great options! 

4. Optimize Sleep for Stress Regulation

How it works: Poor sleep increases cortisol production, making stress worse (Hirotsu et al., 2015). Deep sleep helps restore brain function.

Try this: Stick to a consistent sleep schedule, avoid screens an hour before bed, and create a relaxing bedtime routine.

5. Change Your Cortisol-Boosting Thoughts

How it works: Negative thinking, like constant worry and rumination, can keep cortisol levels high. Studies show that negative thoughts make stress feel worse and lead to more cortisol in the body (Zoccola & Dickerson, 2012). However, changing these thought patterns can change your brain for the better - see our neuroplasticity post from this same series for more about this! Rethinking stressful situations in a healthier way can help the brain adapt and lower cortisol over time, supporting better mental health (Brockman et al., 2017).

Try this: When you catch yourself thinking, "I can’t handle this," shift to, "I’ve handled challenges before, and I can do it again." or “I am capable of handling this and I will grow from it.”

6. Eat Intentionally for a Calmer Brain

How it works: Certain foods can help regulate cortisol levels and balance brain chemistry, leading to reduced stress and a calmer mind. Incorporating specific nutrients and dietary patterns can positively influence your body’s stress response.

Try this:

Eat more:

• Vitamin C-rich foods (e.g., oranges, bell peppers) – Shown to lower cortisol from chronic stress (Beglaryan et al., 2023).
• Omega-3 fatty acids (e.g., salmon, flaxseeds) – Help regulate stress hormones (Carvalho et al., 2018).
• Green tea and Matcha – Reduce cortisol and lower stress (Hintzpeter et al., 2014; Unno et al., 2018).
• B Vitamins (e.g., whole grains, eggs) – Linked to lower stress and anxiety (Mahdavifar et al., 2021).
• Mediterranean Diet Foods (e.g., olive oil, nuts) – Reduce stress-related inflammation (Shively et al., 2020).

Reduce:

• Caffeine – Can spike cortisol and increase anxiety (Lovallo et al., 2005).
• Refined sugar – Linked to higher cortisol and impaired stress response (Walker et al., 2014).
• Processed foods – Can increase cortisol and inflammation (Knüppel et al., 2017).

Final Thoughts: You Have the Power to Rewire Your Brain

Stress is part of life, but it doesn’t have to control you. By understanding how cortisol affects your brain, you can start making small, science-backed changes to reduce stress, rewire negative patterns, and build long-term resilience. 

Where will you start? Whether it’s mindful breathing, movement, reducing alcohol consumption, or getting better sleep, each small step helps retrain your brain for a calmer, more focused life.

We hope you enjoyed this blog post. Feel like you're ready for more?

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