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Essential Science: Is anxiety linked to our gut microbiome?

Posted May 27, 2019 by Tim Sandle
Microbiome research has advanced considerably since the first results from the U.S. National Institutes of Health led Human Microbiome Project were released. One area of interest is the connection between our microorganisms and anxiety symptoms.
Untitled
Sander van der Wel (CC BY-SA 2.0)
At first glance, the connection between the array of different microorganisms that are found within the human gut and feelings such as anxiety is not an obvious one. However, there is a growing level of evidence that variations within microbial communities are influential upon metabolic processes.
Human microbiome
The human microbiome refers to the totality of microorganisms and their genetic interactions within a given niche. Our understanding of the microbiome has advanced following a study of 300 men and women, who volunteered to take part in an international study. The advancement in understanding relating to developments with the methods used to characterize the microorganisms (including metagenomics) and the in-depth nature of the study, relating to the sampling of many body parts over a prolonged period of time, and drawing upon of the subjects from different geographical locales.
FDA microbiologist prepares DNA samples for gel electrophoresis analysis
FDA microbiologist prepares DNA samples for gel electrophoresis analysis
FDA / File
With the specific effects in relation to the human gut, then the understanding by scientists of the gut-brain axis has increased during the past ten years, suggesting a bidirectional nature between the gut and brain microbiome interactions. This includes a connection relating to the pathophysiology and pathogenesis of irritable bowel syndrome (IBS), as an example.
In another research field, there is growing evidence of psychiatric and neurologic disorders like autism spectrum disorders, affective disorders, Parkinson's disease, and multiple sclerosis, being connected to the human gut microbiome.
The reason for this is that, with most people, the gut microbiota assist with the healthy functioning of the immune system. Furthermore, organisms assist with the metabolism by contributing inflammatory mediators, vitamins, and nutrients. Moreover, microbiologists have demonstrated that the intestinal microbiota can modulate communication between the intestinal tract and human brain via the nervous, immune, and endocrine systems.
It may be possible to treat superbugs with a predatory bacteria.
It may be possible to treat superbugs with a predatory bacteria.
University of Nottingham
However, when the intestinal microbial balance is altered, then changes occur and these can be manifest in terms of physical, and potentially mental, symptoms. One area being investigated in relation to a mental system is anxiety.
Anxiety
Anxiety is an emotion characterized by an inner turmoil. It is often accompanied by nervous behaviour, somatic complaints, and rumination. The condition includes subjectively unpleasant feelings of dread over anticipated events. When experienced regularly the individual may suffer from an anxiety disorder. The global incidence of anxiety disorder is estimated to be between 3-25 percent. Typical treatment for anxiety is usually psychopharmacological therapies and psychotherapy.
New research
With the new research, scientists have attempted to see if anxiety symptoms can be improved by regulation of intestinal microorganisms. By assessing some 3,334 published articles the researchers focus on 21 major studies. Across these studies,1,503 participants included "patients with IBS (10 studies), healthy controls (six studies) and other patients with chronic diseases such as chronic fatigue syndrome (CFS), rheumatoid arthritis (RA), obesity, fibromyalgia, and type 2 diabetes mellitus."
Of the 21 studies, 14 had chosen probiotics as interventions to regulate intestinal microbiota (IRIFs), and seven chose non-probiotic ways, such as adjusting daily diets. Those studies that utilized "interventions regulating intestinal flora" consisting of probiotics with Lactobacillus alone or a mixture of Lactobacillus, Streptococcus, and Bifidobacterium, showed some positive results. Overall, 11 of the 21 studies suggested a positive effect on anxiety symptoms by regulating intestinal microbiota, meaning that more than half (52 percent) of the studies showed this approach to be effective.
Some of the bacteria found by scientists in 3.5-billion-year-old fossils are now extinct  while oth...
Some of the bacteria found by scientists in 3.5-billion-year-old fossils are now extinct, while others are similar to contemporary microbes
MARTIN BERNETTI, AFP/File
To draw these conclusions the review was subjected to meta-analysis, considering the research design, subjects, interventions, and anxiety assessment scales. This drew out the connected between anxiety and disturbances to the gut microbiome and indicated that it may be possible to regulate the intestinal microbiota through the use of probiotics, although further research will be required.
The researchers conclude: "We find that more than half of the studies included showed it was positive to treat anxiety symptoms by regulation of intestinal microbiota.
"There are two kinds of interventions (probiotic and non-probiotic interventions) to regulate intestinal microbiota, and it should be highlighted that the non-probiotic interventions were more effective than the probiotic interventions. More studies are needed to clarify this conclusion since we still cannot run meta-analysis so far."
Research paper
The new research has been published in the British Medical Journal, with the research paper titled “Effects of regulating intestinal microbiota on anxiety symptoms: A systematic review.”
Essential Science
A computer-generated image of the International Prototype kilogram (IPK)  which is made from an allo...
A computer-generated image of the International Prototype kilogram (IPK), which is made from an alloy of 90% platinum and 10% iridium (by weight) and machined into a right-circular cylinder (height = diameter) of 39.17 mm. The IPK is kept at the Bureau International des Poids et Mesures (International Bureau of Weights and Measures) in Sèvres on the outskirts of Paris.
Greg L (CC BY-SA 3.0)
This article is part of Digital Journal's regular Essential Science columns. Each week Tim Sandle explores a topical and important scientific issue. Last week we learned how the original kilogram is no more, or at least it will remain locked in a Paris vault never to be used for official purposes, such as calibrating national weight standard again. Instead there’s a new approach for assessing global mass.
The week before we considered how big data analytics is being used to assess and to make predictions about human health.