Stress, cortisol and your brain

When you are in a situation you perceive as dangerous, your body responds to give you more energy, keeping you alert and switching you into emergency response mode. When this stress response kicks in, energy is directed to your brain and muscles enabling you to respond to the threat. This is often referred to as the fight or flight response - where you fight for survival or flee as fast as you can from the situation.

In evolutionary terms, this is a remarkable system that has helped our species survive. Imagine one of our early ancestors emerging from their cave and suddenly finding themselves face to face with a tiger. At that moment, they needed every muscle in their body to be working to its peak ability, and their brain to be on high alert to deal with the situation.

Fortunately, most of us today are unlikely to meet a tiger first thing in the morning, but the stress response is still needed to help us deal with perceived threats; the sound of breaking glass in the middle of the night, a gang in a dark street, the prospect of losing your job or the car in front suddenly breaking. Of course, everything in life is subjective and how they are perceived varies according to different people. A situation that is emotionally stressful for one person may be exciting for another; doing a sales pitch, an important meeting, moving house, meeting your new boss. We all process things differently and attach different meanings to events based on our experiences, interpreting results in different ways. If you feel you have delivered a piece of work at a lower standard than usual then you may feel worried that your competence will be criticised, yet your colleague may just brush it off as a one-off.

There are three main parts of your body responsible for the stress response - your hypothalamus and pituitary, both located in your brain and your adrenal glands, situated one on top of each of your kidneys.

Once your brain decides there's danger, the sympathetic nervous system prepares your body for action and sends nerve signals down your spinal cord to your adrenal glands telling them to release the hormone adrenaline. This increases the amount of sugar in your blood, accelerates your heart rate, raises your blood pressure and dilates your pupils, bronchial passages and coronary arteries. You begin to breathe more quickly to enable you to absorb more oxygen, and your faster heart rate and raised blood pressure ensures you pump maximum oxygen and energy-rich blood to your muscles while your liver releases more sugar into your blood to release more energy. While blood flow to the muscles and organs is prioritised, blood flow to the surface of the body decreases, which explains the phrase "she turned white as a sheet". Gastro intestinal activity also falls, which can lead to a feeling of 'butterflies' in the stomach.

And finally, when you perceive that the threat has passed, your parasympathetic nervous system helps to restore your body to a state of equilibrium.

The amazing thing is, that you can go through this entire sequence in a fraction of a second!

The curse of cortisol

Without cortisol you would die, as it is critical in keeping your blood sugar and blood pressure high to help you escape from danger and optimally cope with life-threatening situations. Your body's stress response is perfectly in tune with cortisol in the short-term, but damaging in the long haul. However, some people perceive every day of their life as stressful. The prolonged effect of the stress response lowers your immune system and raises blood pressure which can lead to hypertension and headaches. This can result in weight gain, particularly abdominal fat, and has a role in osteoporosis, digestive problems, hormone imbalances, cancer, heart diseases and diabetes. Adrenal fatigue can result in physical symptoms such as 'tired but wired', weakness, low blood pressure, dry skin, digestive problems, low blood sugar, cravings for sweet, starchy food, feeling faint, etc.

If stress is more sustained, the raised cortisol has negative effects for your brain as well as your body. It has a domino effect on your mental health and can be a disaster for your brain function.

Your brain cells can die

Cortisol released during stress travels into the brain and binds to the many neuron receptors. Through a series of reactions, this causes neurons to take in more calcium and, if they become over-loaded with calcium, they fire too frequently and die.

Cortisol and the BDNF protein

Neurotrophins are molecules that promote the development, health and survival of brain cells. Among the neurotrophins, brain-derived neurotrophic factor (BDNF) is a major regulator of synaptic plasticity and neuron survival - processes that have key roles in memory formation and learning. BDNF is a protein that is central to keeping brain cells healthy and to stimulating new ones to form through neurogenesis. Just like eating protein for muscle growth, BDNF is the protein for your neurons - it's like the ultimate brain super-food. But the raised cortisol of stress stops the production of BDNF, so fewer brain cells are formed. Forget super-food and enter a deprived diet.

At the Weizmann Institute of Science in Israel, a team of researchers looked at young and adult rats to see if healthy BDNF levels could help dampen stress and manage the level of cortisol secreted1. In the study, rats were subjected to 4 weeks of chronic mild stress to induce depressive-like behaviours. One group had the BDNF reduced and the other increased. The results showed that a reduction of hippocampal BDNF in young, but not adult, rats induced prolonged increases in corticosterone secretion (cortisol is the predominant glucocorticoid in humans, whereas corticosterone is the dominant glucocorticoid in rodents). They also found that hippocampal BDNF plays a critical role in the development of neural circuits that control adequate resilience to chronic stress. In summary, BDNF matters - and particularly so for young rats.

BDNF and ageing

It will come as no surprise that, like many other chemicals in the human body, aging decreases BDNF levels. That's why it takes you longer to learn to do complex tasks as you get older. Remember, the protein is instrumental in learning quickly and learning well.

Lowered levels of BDNF are also associated with neurodegenerative diseases such as Alzheimers, Parkinsons and Huntingdon disease, although the research is in its infancy to truly understand the cause and potentially create BDNF therapies.

Cortisol and Dementia

A Brazilian Study in 2013 of 309 elderly people (from a common genetic background living in the same area) showed that chronic stress and elevated cortisol contributes to dementia in the elderly and speeds up its progression2. They found that concentrations of cortisol are higher in people with dementia, intermediate in people with cognitive impairment but no dementia (CIND) and lower in the healthy elderly control group. The researchers found that the elevated cortisol levels could be a result of hippocampal damage - part of the brain implicated in the regulation of cortisol. Or the results could be that the people with higher levels may have had higher cortisol levels during their lives which could have caused hippocampal decline, possibly triggering the Dementia or CIND. As with much of the research in neuroscience, this study offers useful information about cortisol and dementia, but further research is needed to look at causal relationships and how this can affect strategies at different stages of life.

Cortisol and depression

Chronic stress has also been linked to depression. A common feature of depression is the excessive release of cortisol in the blood which can reduce the levels of critical neurotransmitters notably serotonin and dopamine, damaging their receptor sites. Low levels of either of these neurotransmitters can leave you depressed and more prone to addictions. Serotonin is often referred to as the happy hormone, playing a major role in mood, learning, appetite control, and sleep. Dopamine is known as the motivation hormone and is related to pleasure or reward and the drive to seek that pleasure. Too little dopamine can leave you unenthusiastic, demotivated, lethargic, and depressed. People low in dopamine often try to give themselves a temporary boost in dopamine levels by drinking coffee, eating sugary sweets and foods or drinking alcohol.

Serotonin-based depression is accompanied by anxiety and irritability, while dopamine-based depression manifests as lethargy and lack of enjoyment of life.

Emeritus Professor of Neuroscience and Cambridge University Jo Herbert, in 2012, in reviewing the relevant studies and literature stated that there is little doubt that cortisol plays a central role in the onset and course of major depression disorder, concluding that the time is now right for serious consideration of the role of cortisol in a clinical context3. In the next few years, as well as increased research into the physical rollercoaster that elevated cortisol takes people on, I am sure we will read more exciting discoveries about the implications for our brains.

How to control your body's stress response

In today's frantic world it is important that we all learn to manage our body's natural response to stress. Experiencing some stress is normal, and sometimes even beneficial for your health, but as we have seen, persistent surges of adrenaline and cortisol can be damaging.

To control adrenaline you need to activate your parasympathetic nervous system, also known as the 'rest and digest' system as it is the opposite of the 'flight or fight' response. According to, the best way to achieve this is by trying the following:

- deep breathing exercises
- meditation
- yoga or tai chi exercises, which combine movements with deep breathing
- talk to friends or family about stressful situations so you're less likely to dwell on them at night
- eat a balanced, healthy diet
- exercise regularly
- limit caffeine and alcohol consumption
- avoid cell phones, bright lights, computers, loud music, and TV right before bedtime

1 Takuaz, D, Loya, A., Gersner, R., Haramati, S., Chen, A. & Zangen, A. (2011) Resilience to chronic stress is mediated by hippocampal brain-derived neurotrophic factor. Journal of Neuroscience, 31(12). 4475-4483.

2 Lara, V.P., Caramelli, P., Teixeira, A.L., Barbosa, M.T., Carmona, K.C., Carvalho, M.G., Fernandes, A.P., Gomes, K.B. (2013). High cortisol levels are associated with cognitive impairment no-dementia (CIND) and dementia. Clinica Chimica Acta, 423, 18-22.

3 Herbert, J. (2013). Cortisol and depression: Three questions for psychiatry. Psychological Medicine, 43(3), 449-469.

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