Gut bacteria linked to depression, study shows

Gut bacteria linked to depression, study shows

Najaf Amin spent two years receiving poop in the mail. The professor and researcher at the University of Oxford, in England, together with her research group, analyzed the material sent by more than two thousand people and concluded that there are bacteria in our body that may be associated with the development of depression.

Scientists use excrement to infer which microorganisms are present in our gut. As the intestinal flora is a direct consequence of food, microbiologists and psychiatrists agree that a healthy diet is a key point in mental health care. The results of the study were published in the scientific journal Nature in December 2022.

There were already many indications that the intestinal flora could affect our mental health. Diseases such as Alzheimer’s, autism and Parkinson’s are some of which can be associated with the bacteria inside our body. For depression, however, there were only studies, with small groups of participants, which led to conflicting results. It was then that Professor Amin decided to shed light on the issue.

In the first phase of the research, stool samples from more than a thousand Dutch people were analyzed to identify the microorganisms present. In addition to collecting and sending the material by mail, the volunteers completed questionnaires to assess the presence of classic symptoms of depression. Then, correlations were made between the bacteria found and people with a greater tendency to develop a depressive condition.

The survey was then repeated on a second group of participants of different nationalities. The new results, when compared with the first ones, coincided in many points. André Uitterlinden, co-author of the study and professor at the Erasmus University of Rotterdam, in the Netherlands, says that “there is replication of an original observation, and this is something that we normally do not see in a scientific article”.

According to the professor, the robustness of the work offers solid evidence of the relationship between the microbiota and mental health. In total, the researchers identified 16 genera of bacteria associated with depression, but for them this is still just the first step.

Depression is a health problem with complex causes, and the authors consider that longitudinal studies are needed, that is, carried out over time, and with even more participants, in order to definitively define its association with the intestinal flora.

Robert Kraaij, who is also a co-author of the work, emphasizes that the relationship between microorganisms in the intestine and depression can occur in two directions. Both depressive behavior can lead to poor diet, causing an imbalance in this ecosystem, and this dysbiosis can interfere with the functioning of the brain. According to them, today the second aspect is of more interest to scientists.

There are three main ways in which this collection of living beings can influence the mind. First, when the microbiota is unbalanced, cytokines can be produced that affect the functioning of the immune system. Another way is through the direct production, by it, of substances that act as signals for the brain, such as GABA or similar to epinephrine.

However, as stated by Leandro Lobo, microbiologist and researcher at UFRJ (Federal University of Rio de Janeiro), attention has been drawn to the mechanism of direct action of the intestinal flora. Laboratory experiments show that, in the process of helping to digest our food, the intestinal flora produces molecules that fall into the bloodstream. Some of them are involved in expression and transcription functions of our own genes.

Professor Amin believes that the diet can become, in the future, the front line in the fight against depression. Compared to using medication, changing your diet is inexpensive and has no side effects. In addition, it brings benefits to other aspects of our life, such as cardiovascular health.

Second, the researcher sees the development of probiotics as a direct consequence of research such as hers. For this, however, she recognizes that much progress is still needed. It is necessary to accurately identify the strains of beneficial bacteria before thinking about a product to supplement the diet. Current work, like yours, only reaches the genus of microorganisms.

According to Adiel Rios, a psychiatrist and volunteer researcher at the Hospital das Clínicas at USP (University of São Paulo), it is becoming common for psychiatrists to ask for nutritional monitoring of some patients.

The expert reinforces the need for a balanced and personalized diet, and believes that more research with solid evidence can support future public policies on diet and nutrition aimed at mental health.

The study of complementary treatments involving dietary factors capable of reducing the symptoms of mental disorders is carried out by nutritional psychiatry, a field that is still emerging in the country. Rios, who works in the area, is working on clinical trials to evaluate the antidepressant effects of probiotics in bipolar patients.

He states that the successful development would represent a new strategy to prevent and treat serious disorders based on the modulation of the microbiota. But until you get there, experts agree that a balanced and individual diet is the best way to keep your body and mind healthy.

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