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Brain cells communicate via chemicals called neurotransmitters. Chronic stress can reduce the levels of these critical neurotransmitters, especially serotonin and dopamine.

Serotonin is the “happy molecule” which plays a large role in mood, learning, sleep and appetite control. When serotonin is low in the body, women become prone to depression, anxiety and binge eating whilst men are more at risk of alcoholism, ADHD and impulse control disorders.

The brain is protected by the blood-brain barrier which is a semi-permeable filter of highly specialized cells which allow nutrients to enter whilst blocking pathogens, heavy metals and other toxins. Stress can effect this barrier, allowing it to become more permeable, making it leaky, which then allows these harmful substances to damage and attack brain cells. This may then predispose people to a variety of mental illnesses including anxiety, panic disorder, bipolar disorder, depression, alcoholism and drug addiction (Alban, 2018).

Around 90 percent of the body’s Serotonin is estimated to be made in the digestive tract by immune cells, nerve cells and enter chromaffin cells. These cells need gut bacteria to produce serotonin. Exposure to even short-term stress can impact the microbiota profile by altering the proportions of good and bad bacteria. This in turn, influences the stress response and the hypothalamic-pituitary-adrenal (HPA) stress axis (Paddock, 2015).

The gut is not just the place of digestion and elimination it also contains our second brain, the enteric nervous system. Sheaths of neurons embedded in the walls of the alimentary canal, or the nine-metre-long tube of the gut, contain reflexes and senses, enabling the second brain to control gut behaviour independently of the brain. Research is being done to understand how the trillions of bacteria in the gut communicate with the enteric nervous system cells. This second brain contains around 100 million neurons, which is more than either the peripheral nervous system and the spinal cord (Hurley, 2018).

There is a direct line of communication that is continual between the brain and the gastrointestinal tract and gut bacteria play a significant role in this communication. When the gut is full of healthy bacteria, it has the potential to regulate positive feelings and mood.

A large part of our emotions are probably influenced by the nerves in our gut. An example is the feeling of butterflies in the stomach, these are signalled in the gut and are part of our physiological stress response. Scientists have found that around 90 percent of the fibres in the primary visceral nerve, the vagus, actually carry information from the gut to the brain and not the other way around.

The microbiota-gut-brain axis communicate in a complex multidirectional manner to maintain homeostasis. Stress is one of the main factors that can disrupt this equilibrium. The health of the microbiome ensures adequate Serotonin production, which in turn helps maintain optimal functioning of the blood-brain barrier and communication of the brain and second brain (Rea, 2016)..


Alban. (2018). 12 Effects of Chronic Stress on Your Brain. Retrieved May 15, 2018, from Be Brain Fit:

Hurley. (2018). Your Gut Can Influence How you feel: It all starts with GABA and serotonin. Retrieved May 15, 2018, from Body Ecology:

Paddock. (2015, April 21). Gut microbes important for serotonin production. Retrieved May 15, 2018, from Medical News Today:

Rea, D. C. (2016, October 4). The microbiome: A key regulator of stress and neuroinflammation. Retrieved May 15, 2018, from Science Direct:

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