- Experts are interested in how the gut microbiota may influence mental health conditions like anxiety.
- One narrative review suggests that people with anxiety can experience decreased microbial diversity and fewer short-chain fatty acid-producing bacteria.
- The finding also suggests that using probiotics could help to improve anxiety symptoms.
The gut microbiota refers to the microorganisms that live in the gut.
A narrative review recently published in the journal Nutrients sought to look at data on changes in the gut microbiota in people with anxiety disorders and on how probiotics may help improve anxiety symptoms.
The results suggest that there are changes like less microbial diversity that occur in people with anxiety disorders. Additionally, probiotics may help adjust the gut microbiota and improve anxiety symptoms.
Through this review, researchers wanted to understand more about changes in the gut microbiota among people with anxiety disorders.
They note that anxiety disorders are some of the most common mental disorders. This makes understanding body changes and identifying ways to help critical.
Researchers conducted a literature search for studies relevant to the topic that were published at any time and written in English. Their review had randomized controlled trials and clinical studies with participants with anxiety disorders.
The examined studies suggested that people with anxiety disorders experienced distinct changes in gut microbiota.
One study found that participants with generalized anxiety disorder had a lower diversity of microorganisms. Participants also had less richness of microorganisms, higher levels of certain bacteria, and lower levels of “bacteria that produce
This study also found that even after participants experienced remission of anxiety, the gut changes remained, indicating the changes may affect generalized anxiety development.
Another study found distinct decreases in certain bacteria and increases in others among participants with generalized anxiety disorder. The increases in certain bacteria were related to how severe the anxiety was, while others were associated with anxiety reduction.
Other research used Mendelian randomization and found five bacterial traits that might increase the risk for anxiety disorders, and four that may decrease the risk.
The review also highlighted a study that reflected on the changes in gut bacteria, noting a “complex relationship between gut microbiota, inflammatory and genetic factors, and the development of anxiety disorders.”
There was also research noting the differences in microbiota between individuals with depression and those with generalized anxiety disorder, which further suggested that looking at the gut microbiota could help determine if someone has a depressive or an anxiety disorder.
Another study identified specific microbes and a metabolite that could help determine the severity of an individual’s depressive symptoms.
Finally, the review cited research that found similar gut microbiota compositions for healthy controls, participants with functional gastroenteropathy (a complication of diabetes), and participants with functional gastroenteropathy and generalized anxiety disorder.
However, they did find a few differences, such as higher levels of Clostridium microorganisms in participants who had anxiety and functional gastroenteropathy.
The review authors wrote that “[s]everal biological mechanisms underpin the connection between bacterial presence/absence in the gut and anxiety symptoms.”
For one, the gut-brain axis connects the gut microbiota and central nervous system. Helpful bacteria like Lactobacillus help produce the neurotransmitter
This neurotransmitter helps control people’s stress response and anxiety. A decrease in the bacteria that produce GABA may be related to worse anxiety symptoms.
Imbalances in the gut microbiota can also contribute to systemic inflammation. Chronic inflammation may then contribute to brain function changes and increased anxiety.
Furthermore, people with generalized anxiety tend to have increases in inflammatory markers, which could be because of gut microbiota changes.
Certain helpful gut bacteria produce short-chain fatty acids that then affect neurotransmitter activity and help decrease neuroinflammation.
Finally, the gut microbiota helps to regulate the hypothalamic-pituitary-adrenal (HPA) axis. When there are imbalances in the gut bacteria, this axis may increase activity too much, and people can thus experience worse anxiety symptoms.
Licensed psychotherapist Noah Kass, DSW, LCSW, who did not participate in this review, told Medical News Today that it “reinforces the connection between gut flora and psychological distress” and “suggests that certain probiotic treatments, especially Lactobacillus strains, may help individuals with anxiety-related disorders.”
The review authors noted that taking supplements like probiotics, using certain spices, and eating fruits and vegetables encourages the growth of helpful gut microbiota while stopping the growth of damaging microorganisms.
Using certain products can also help people develop good dietary habits that help prevent and improve symptoms of emotional disorders.
Authors also note that some evidence suggests that taking probiotic supplements, especially those that have Lactobacillus rhamnosus, could help with stress response regulation and decrease the hyperactivity of the HPA axis.
Regarding probiotic use, Kass also explained that:
“Some gut bacteria produce GABA and serotonin, neurotransmitters that regulate emotions and stress responses. Research shows a link between gut health and mental well-being. Taking probiotics can influence this balance, making individuals more resilient to stress, which may benefit those with anxiety-related disorders.”
The review authors further examined several studies that tested the benefits of certain probiotics for mental health. Several focused on bacteria in the Lactobacillus genus.
One study observed that supplemental use of probiotic Lactobacillus plantarum JYLP-326 appeared to help lessen symptoms of insomnia, anxiety, and depression among participants.
Another found that using Lactobacillus plantarum P8 may help decrease inflammatory cytokines (signalling proteins in the immune system), decrease stress and anxiety, and improve cognitive performance.
Yet another study suggested a benefit of Lactobacillus rhamnosus CNCM in improving stress-induced anxiety, though other research found no benefit compared to controls.
The review also cited research indicating that probiotic use did not impact either the heart rate or the electrodermal responses of participants, but the intervention group did have improved reaction times.
Other research examined methamphetamine-addicted participants, and found no improvement in anxiety and psychotic symptoms. However, it found improved appetite and sleep quality in participants who received Lactobacillus acidophilus
Finally, one study found that Lactobacillus gasseri CP2305 appeared to help with anxiety and sleep disturbance.
The review authors also looked at studies that examined the genus Bifidobacterium. One of these found that Bifidobacterium longum did not appear to help reduce stress, depression, or anxiety, but the study was of short duration and only used one probiotic strain.
However, another study found that B. longum may help decrease the stress response and may affect decreases in anxiety and depression symptoms. The use of Bifidobacterium breve A-1 in participants with schizophreniaalso appeared to help with anxiety and depression.
Finally, the review authors looked at studies that examined multicomponent formulations. One study that used Lactobacillus Helveticus R0052 and Bifidobacterium Longum R0175 found improvements in anxiety, depression, and stress. Another also suggested that probiotics could help reduce anxiety.
In contrast, a study of participants with generalized anxiety disorder found that probiotics that contained four bacterial strains influenced some assessment scores and not others.
This research found that quality of life was the same for the intervention and control groups and that trait-anxiety inventory scores were similar. One assessment of anxiety reduction did not reach a statistically significant level for the probiotic group, but the other indicated reduced anxiety.
This review suggests another potential way to help people with anxiety disorders. However, a review like this also has limitations.
For one, researchers only included studies written in English, so they were not looking at possibly relevant papers written in other languages. They used only four databases, and other databases could have revealed additional results.
The authors further cautioned their findings could have been impacted by their broad inclusion criteria, such as including studies published at any time or including studies of any anxiety disorder rather than focusing on a specific type.
Finally, studies included also had limitations, on a case by case basis. For example, some studies had small sample sizes and focused on specific groups of people, so additional studies to confirm the results may be helpful.
Looking into more specifics could also be highly beneficial for future research.
Ashkan Farhadi, MD, a board-certified gastroenterologist at MemorialCare Orange Coast Medical Center in Fountain Valley, CA, who was not involved in this review, commented that “it’s a well-done review of all those nuances in the connection of gut bacteria and [the] central nervous system.”
At the same time, he also emphasized that we are limited in our current understanding of probiotics. He explained to MNT that:
“Our understanding of probiotics is really rudimentary. Basically, we know there are germs in the gut, and we know that they are doing something […] We just have a crude idea by adding a few germs that we know are benevolent to the population […] We really don’t know what they’re doing, how they are communicating, and what’s happening there.”
The review authors also noted that exploring the best way for people to receive probiotics and how to personalize treatments that focus on influencing the gut microbiota will be helpful in the future.
