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Researchers Explore Gut Bacteria–Depression Links

An intestine with gut bacteria in it is drawn on a stomach
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Researchers at Oxford Population Health, along with colleagues in the Netherlands, have demonstrated that 13 types of bacteria found in the gut are associated with symptoms of depression. These bacteria are known to be involved in the production of neurotransmitters that play a key role in depression, such as serotonin and glutamate. The study is published today in Nature Communications.

Depression is one of the most common mental disorders experienced worldwide, with approximately 280 million people having the condition. The treatment options available to people with depression are sub-optimal for many patients and can come with debilitating side effects. Depression is poorly understood as it has been difficult to identify exactly how the changes in neurotransmitters in the brain develop. Although depression is primarily a mental health problem, patients show a wide range of physical problems including disturbances in food intake and a marker increase in the brain and blood.

Evidence is accumulating that bacteria living in the gut may be able to influence brain activity and behaviour. This may lead to the development of novel treatments for various neuropsychiatric disorders including depression. The researchers from Oxford Population Health investigated the relationship between the gut microbiome composition and diversity, and symptoms of depression in over 1,000 participants of the Rotterdam Study. The findings were then replicated and validated in over 1,500 participants in the Amsterdam HELIUS study. None of the study participants were using antidepressants for an active depression when their stool samples were collected; the degree or amount of their depressive symptoms were used to demonstrate susceptibility to depression.

The researchers aimed to identify gut microbiota associated with depressive symptoms in the general population and only included individuals who were not taking antidepressants to avoid measuring changes in the gut microbiome that are a consequence of the depression rather than a cause.

Key findings:

  • 13 types of bacteria (12 genera and one family) were found to be positively associated with symptoms of depression;
  • The study found convincing, replicable evidence for an increase in Sellimonas, Lachnoclostridium, Hungatella and decrease in Ruminococcus, Subdoligranulum, LachnospiraceaeUCG001, Eubacterium-ventriosum and Ruminococcusgauvreauiigroup in the guts of individuals with more depressive symptoms;
  • This confirmed the findings of earlier studies suggesting there is an increase in Eggerthella and decrease in Coprococcus, Subdoligranulum, and the Ruminococcaceae family at large in those with more depressive symptoms;
  • The discovery of the association between Sellimonas and symptoms of depression is the most significant novel finding of this study. Species of bacteria belonging to the Sellimonas genus are involved in various inflammatory diseases and may be relevant for the inflammation seen in patients with depression; 
  • Various microbiota identified in the study showed potential involvement in the way our bodies produce neurotransmitters that are related to depression such as glutamate, which is in turn relevant for the treatment and prevention of depressive symptoms.

Dr Najaf Amin, co-corresponding author and Senior Research Associate at Oxford Population Health, said ‘The prevalence of depression, which has increased significantly as a result of the COVID-19 pandemic, and the devastating effect it can have on people’s lives has created a pressing need to improve our limited understanding of it. The results of this study provide new grounds for research into how changing the gut microbiome through diet could reduce the symptoms of depression, which could ultimately improve many people’s lives.’

Reference: Radjabzadeh D, Bosch JA, Uitterlinden AG, et al. Gut microbiome-wide association study of depressive symptoms. Nat Commun. 2022;13(1):7128. doi:10.1038/s41467-022-34502-3

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