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effects of stress on the brain how to reduce cortisol levels stress and the brain what is the fight or flight response natural stress relievers

The effects of stress on the brain and 5 ways to de-stress

Published Nov 1, 2022 | Updated Feb 8, 2024

The National Institute of Mental Health defines stress as, “the body’s response to a demand” [1]. Stress challenges the stable state that the body strives to maintain at all times. The stress response is your body working to re-establish its zen mode when challenged [2]. It is designed to be your body’s protective mechanism and has evolved over 500 million years to defend you [2].

What is the fight or flight response?

When faced with a stressor, whether it be public speaking or being in physical danger, your body has a fine-tuned system of reactions to respond to it. This chain of reactions is the “fight or flight” response where the body gauges the situation and prepares you to either fight the situation (being brave and delivering a great speech) or flight (running to safety from the threat) [3].

Stress and the brain: what happens? [4][5]

  1. The first sign of a stressful event is picked up by the brain’s emotion centre.
  2. This message is quickly sent to the control centre of the brain which alerts the whole body and starts the response process.
  3. The brain prioritizes bodily functions within seconds: 
  4. Heart rate and breathing increases, Blood flow increases, Sight, smell, and hearing senses are alerted, Blood sugar rises to increase energy production
  5. 10 seconds after the initial response, the brain activates the stress response system that releases cortisol, the stress hormone [6] 
  6. Cortisol carries the stress response forward by increasing glucose and blood supply to the muscles for the body to fight/flight. It increases blood pressure and keeps only the essential systems activated to help the body respond efficiently. Cortisol levels can remain high for hours after the stressful event.
  7. When the situation resolves, cortisol levels drop, and bodily systems return to normal.

Chronic stress: effect on the brain

Short term stress repeated often becomes chronic stress. In today’s fast-paced lives, there are many sources of stress. This has an impact on your brain because your stress response is constantly activated. Chronic stress can cause the following brain changes:

  1. The brain cells that participate in this process are sensitive and over time, they change structurally due to the pressure, affecting their ability to make connections.
  2. Long term stress (more than 12 weeks) can affect short term and long-term memory [7], by decreasing production and connection of new brain cells. There are ways in which this can be corrected. 
  3. Frequent high levels of cortisol can damage brain cells, accelerates their aging, and contributes to increased risk of Alzheimer’s disease [7]. Cortisol levels can be managed to help lower this risk. 
  4. Your brain strengthens the parts that are frequently used over those that are used less. Constant activation of the stress response system increases focus on survival instinct and decreases focus on the brain system involved with complex thinking, decision making, personality development and social behaviour [8].
  5. Chronically high cortisol levels can decrease the size of your brain structures. Those who had a constantly high cortisol level had smaller sized brain structures involved in learning, memory, and other cognitive skills compared to those with a well-regulated cortisol levels [9]

Stress management: How to reduce cortisol levels?

Cortisol is beneficial in small doses, as long as it is well regulated. The good news is cortisol and stress are adaptable and the effects of stress can be easily managed. You can employ evidence-based strategies to help manage your stress and protect brain health:

1. Practice relaxation response

Over 40 years ago, Dr Herbert Benson, professor at Harvard Medical School developed the relaxation response, a stress management technique that has been researched for it benefits [10]. He describes it as a strategy to counteract the fight or fight response and thus lower the impact of stress. 

The relaxation response involves the following steps:

  • Sit comfortably in a quiet environment with eyes closed
  • Relax your muscles and focus on deep breathing
  • Chant words if you need to focus on the process
  • Continue for 10-20 mins allowing the mind to relax

The technique is like meditation and has shown to decrease cortisol levels (in 50% of participants), lower blood pressure (in 32% of participants), decrease anxiety levels and improve mental wellbeing. [11][12]

2. Boost your diet

It is important to ensure intake of all essential nutrients for optimal brain functioning because nutrients work in harmony. 2 notable mentions that have been studied for a better stress response include L-theanine and omega 3:

  • L-theanine is a nutrient found in green tea and promotes relaxation without sedation. 200 mg of L-theanine reduced stress levels an hour after intake and reduced cortisol levels after 3 hours [21]. It increases the relative concentration of the relaxing brain chemical, GABA, which is decreased during stress [22]. Research studies employ high doses of L-theanine, which is easier to acquire through supplementation compared to increasing food intake. Brain feed’s L-theanine is naturally extracted from green tea and provides 250mg L-theanine which is equivalent to 15-20 cups of green tea. Browse natural theanine from only £15.99. Additional 15% off your 1st order using code NEW15
    • Omega 3 are healthy fats that are found in the brain. These can be taken from the diet by increasing intake of fatty fish, nuts, and algae. Participants who had 3 weeks of omega 3 fish oil supplementation reported a decrease in stress symptoms and cortisol levels [19]. Additionally, omega 3 fats were shown to reduce the brain cell damage caused by cortisol and also promoted new brain cells production [20].

    3. Get moving

    Regulating the stress response system to improve efficiency of recovering the zen mode is the goal of stress management. Physical activity is one of the best natural stress relievers. Physically fit people respond better to stress. Some studies showed that higher the intensity of physical activity, more efficient is the regulation of stress response [13]. Even a simple activity like walking for 30 minutes is known to reduce cortisol levels [14]. This effect is heightened in a nature environment. In Japan, this practice is called “forest bathing” and a review of 8 studies reported that it decreased cortisol levels [16]. 70% of participants who went on a 15-mins walk in a forest (nature), had an average 14% decrease in cortisol levels after the walk [15].

    4. Spend time with pets

    Owning a dog or cat can be beneficial for mental wellbeing. A review of 69 studies reported pet owners and positive interactions with animals was associated with better mood and lower cortisol levels. In some cases, cortisol levels dropped by around 50% in the presence of a dog [17]. Stressed university students who interacted with cats or dogs for 10 mins had a significant decrease in cortisol levels [18].

    5. Re-frame stress

    You are in control of your mind. How you respond to stress determines the impact it has. Practising mindfulness and progressive muscle relaxation are 2 ways you can reframe stress to make it work for you. Read more about these here.


    1. National Institute of Mental Health (NIMH). (n.d.). I’m So Stressed Out! Fact Sheet. [online] 
    2. Ortega, V. A. et al. (2021) Evolutionary Significance of the Neuroendocrine Stress Axis on Vertebrate Immunity and the Influence of the Microbiome on Early-Life Stress Regulation and Health Outcomes. Front. Microbiol. 12:634539.
    3. Heckman, W. (2019). How the Fight or Flight Response Works - The American Institute of Stress. [online]
    4. Chu B, et al (2022). Physiology, Stress Reaction. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing;
    5. Hannibal, K. E., et al. (2014). Chronic stress, cortisol dysfunction, and pain: a psychoneuroendocrine rationale for stress management in pain rehabilitation. Physical therapy94(12), 1816–1825.
    6. Guy-Evans, O. (2021). Hypothalamic-Pituitary-Adrenal (HPA) Axis | Simply Psychology.
    7. Alkadhi, K. (2013). Brain Physiology and Pathophysiology in Mental StressInternational Scholarly Research Notices, vol. 2013
    8. Woo, E. et al. (2021). Chronic Stress Weakens Connectivity in the Prefrontal Cortex: Architectural and Molecular Changes. Chronic stress (Thousand Oaks, Calif.)5, 24705470211029254.
    9. Lupien, S. J. et al. (2018). The effects of chronic stress on the human brain: From neurotoxicity, to vulnerability, to opportunity. Frontiers in neuroendocrinology49, 91–105.
    10. Benson, H. (1997). The Relaxation Response: Therapeutic Effect. Science, 278(5344), pp.1693b1697
    11. Dusek, J. A., & Benson, H. (2009). Mind-body medicine: a model of the comparative clinical impact of the acute stress and relaxation responses. Minnesota medicine92(5), 47–50.
    12. Zappella, M. et al. (2021). Relaxation Response in Stressed Volunteers: Psychometric Tests and Neurotrophin Changes in Biological Fluids. Frontiers in psychiatry12, 655453.
    13. Caplin, A. et al. (2021). The effects of exercise intensity on the cortisol response to a subsequent acute psychosocial stressor. Psychoneuroendocrinology131, 105336.
    14. Wood, C. J. et al. (2018). Physical fitness and prior physical activity are both associated with less cortisol secretion during psychosocial stress. Anxiety, stress, and coping31(2), 135–145.
    15. Kobayashi, H. et al. (2019). Combined Effect of Walking and Forest Environment on Salivary Cortisol Concentration. Frontiers in public health7, 376. 
    16. Antonelli, M. et al. (2019). Effects of forest bathing (shinrin-yoku) on levels of cortisol as a stress biomarker: a systematic review and meta-analysis. International journal of biometeorology63(8), 1117–1134.
    17. Beetz, A. et al. (2012). Psychosocial and psychophysiological effects of human-animal interactions: the possible role of oxytocin. Frontiers in psychology3, 234.
    18. Pendry, P. et al. (2019). Animal Visitation Program (AVP) Reduces Cortisol Levels of University Students: A Randomized Controlled Trial. AERA Open, 5(2), p.233285841985259.
    19. Barbadoro, P., Annino, I., Ponzio, E., Romanelli, R. M., D'Errico, M. M., Prospero, E., & Minelli, A. (2013). Fish oil supplementation reduces cortisol basal levels and perceived stress: a randomized, placebo-controlled trial in abstinent alcoholics. Molecular nutrition & food research, 57(6), 1110–1114.
    20. Borsini, A. et al. (2020). The role of omega-3 fatty acids in preventing glucocorticoid-induced reduction in human hippocampal neurogenesis and increase in apoptosis. Translational psychiatry10(1), 219.
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    22. Mody, I., & Maguire, J. (2012). The reciprocal regulation of stress hormones and GABA(A) receptors. Frontiers in cellular neuroscience6, 4.

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