Depressive disorders are one of the leading causes of disability worldwide and it is estimated that they affect around 322 million people. The treatment of depression is not always effective and understanding its causes would help to find new therapeutic alternatives to prevent or minimize depressive symptoms. The intestinal microbiome, which is the set of microorganisms –bacteria, viruses, fungi, protozoa…– present in our intestine and their genetic material, has already been associated with multiple diseases and may also play a key role in depression.
New research has shown that the composition of the gut microbiota can influence cognition and emotions through numerous pathways, known as the gut-brain axis, so modifying this microbial community could become an effective therapy against depression, and even help prevent its onset. In fact, two new studies have now identified gut bacteria linked to depression.
Intestinal bacteria implicated in the development of depression
Led by Jos Bosch of the University of Amsterdam in the Netherlands, one study involved 3,211 people from the HELIUS microbiome cohort, made up of six ethnic groups—including Dutch, South Asian Surinamese, African Surinamese, Ghanaians, Turks and Moroccans – residing in the urban areas of Amsterdam.
The findings “represent a step forward in understanding the inflammatory changes associated with depression and the connection between our digestive flora and brain function”
The researchers linked the microbiota data with demographic, behavioral, and depression data and identified a predictive microbial signature of depressive symptoms that was largely invariant across the ethnic groups studied. The results have been published in Nature Communications.
The second study has also been published in Nature Communications and has been carried out by the team of Najaf Amin, from the Erasmo Medical Center in Rotterdam. Its authors investigated the relationship of the diversity and composition of the fecal microbiome with depressive symptoms in 1,054 individuals from a separate cohort in the Netherlands, called the Rotterdam Cohort, and found 13 groups of related organisms or microbial taxa associated with depressive symptoms, such as Eggerthella, Subdoligranulum and Coprococcus.
The study authors found that these bacteria are involved in the synthesis of chemical messengers known to be associated with depression, such as glutamate, butyrate, serotonin, and gamma aminobutyric acid (GABA). Their findings were validated in the Amsterdam HELIUS cohort in 1,539 people.
Eduard Vieta, scientific director of the Mental Health Network Biomedical Research Center (CIBERSAM), told SMC Spain that, although the results of these studies “are not extraordinarily novel (only in a small part), “they confirm the changes in the microbiome already described and they do so in one of the largest samples to date. In addition, they do so by measuring the severity of depressive symptoms and controlling for the coexistence of other pathologies and the effects of treatment”.
And he adds that: “Changes are identified in the bacterial populations of people with depression related to microorganisms that produce glutamate and serotonin, among other neurotransmitters, which are precisely of great relevance in depression. In addition, these changes are maintained beyond the cultural, genetic and lifestyle differences of different ethnic groups. Despite the large sample, some analyzes could not be replicated but, in my opinion, it represents a step forward in understanding the inflammatory changes associated with depression and the connection between our digestive flora and brain function.”
According to this specialist, “Causality cannot be established, although it is assumed that chronic stress produces inflammation and that is what alters the microbiota, but we also do not know if some of the changes are compensatory.” “It is still too early to talk about treatments. On the one hand, there are indications that a balanced diet (for example, the Mediterranean diet) can improve mental health, although it is not an adequate treatment by itself for major depression. On the other hand, it would be premature and fanciful to consider fecal transplantation today as a therapeutic alternative”, he concludes.
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