The link between gut microbiota and mental health

Gut dysbiosis may be a risk factor for depression.

Tackling a stressful situation or one that causes distress, fear or sadness often manifests in physical symptoms like stomach pain or discomfort. This is because the gut is home to millions of neurons that constantly interact with the immune, endocrine and central nervous systems. This is why the gut is known as the second brain. As Ana Mayor, an internist and expert in Digestive Health at SHA Wellness Clinic, explains, “the intestinal microbiota has an impact on emotions and cognition because it engages in two-way communication with the brain. The reason is that certain gut bacteria produce neurotransmitters in enteroendocrine cells, which act as second messengers in the brain and regulate mood and cognitive functions”.

Neurotransmitters and endocrine signals travel along this two-way road, known as the gut-brain axis, connecting the two organs and explaining the relationship between the microbiota and memory, learning, anxiety, stress, neurodegenerative disorders and neurodevelopment. “The state of the microbiota influences the proper functioning of the brain and the central nervous system”, Ana says, “but there are also signals in the other direction. In other words, our mental and psychological state is reflected in the balance of the gut microbiota”.

Therefore, she continues, “stress has a highly negative impact on the stability of the micro-organisms that live in our gut and, in turn, the gut microbiota conditions the response to stress and its associated sequelae. The most commonly reviewed stressors include psychological stress, disruption of circadian cycles, sleep deprivation, environmental changes (heat, cold, extreme altitude), toxic substances, pollutants, noise, physical activity and diet. All of these have been shown to alter the composition, function and metabolic activity of the microbiota”.

It comes as no surprise, then, that microbiota imbalance is considered a risk factor for depression. ”Serotonin is the most important mediator that allows the microbiota to communicate with both the gut and the brain. In a situation of gut dysbiosis there can be a deficit of bacteria producing gamma-aminobutyric acid (GABA), which is the precursor of serotonin. And this leads to a greater tendency towards depression or to symptoms persisting in the event of an existing depression“, concludes the expert.

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