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Probiotics Can Reduce Stress and Improve Mood. Here’s Why

Most of the focus for probiotics has been on gut health, and to date, almost all of the studies on the brain boosting potential of probiotic strains have been done in mice. In preparation for this post, our research team found two compelling studies, both in humans, which could signal good news for those exploring how the health of the microbiome plays a role in our mental health.

Our regular readers know that we been write a good bit about the microbiome. I wrote previously about how gut bacteria can influence tumor growth.

In that post, I looked at two commercially available strains of probiotic, B. Longum and B. Breve, and how administration helped slow tumor growth in mice who had previously grown tumors at an accelerated pace.

It turns out that certain strains of bacteria can actually enhance cognitive ability while lowering the stress hormone cortisol.

Cognitive impact of probiotics

Dubbed “psychobiotics,” these probiotic strains could be part of the way we treat anxiety and depression in the future, as well as chronic conditions like IBS, which are tied to imbalances in the gut-brain axis.

One of those strains, Bifidobacterium longum (B. Longum), is the focus of my post today. B. Longum is one of the leading probiotic strains associated with cognitive enhancement.

As I noted in my tumor post, the science surrounding the microbiome is new and emerging, and as such, many of the studies have been performed on mice.

However, the first study I want to focus on here looked at the impact of a specific strain of B. Longum (1714) on brain activity patterns, cognition, and the stress response in humans. The double blind and placebo controlled study appeared in the Journal of Translational Psychiatry. This wasn’t a probiotic blend, the authors only evaluated the impact of just this single strain of bacteria: B. Longum 1714. 1

It’s also worth noting that the authors used male subjects, as menstrual cycle can impact cortisol levels, and prior use of probiotics excluded subjects, most of whom ended up being medical students.

This was also a small study at just 22 participants.

Impact on probiotics on stress

The findings on stress were interesting.

Study subjects taking B. Longum had a lower amount of stress in response to a stressful event as well as lower levels of daily reported stress. Cortisol levels dropped after administration of B. Longum 1714.

The psychobiotic effect on the acute stress response is complemented by a reduction in daily perceived stress that is consistent with previous findings that a probiotic intervention can affect subjective everyday stress.

Probiotics impact on cognitive performance

Subjects administered B. Longum 1714 showed subtle improvements in visuospatial memory as well as enhanced prefrontal cortex activity (the part of the brain linked to willpower) based on an electroencephalogram (EEG) test. So, bottom line, B. Longum, or at least B. Longum 1714, was shown to reduce stress and modestly improve beneficial brain activity.

For a couple years, the Translational Psychiatry study (“TS study”) stood alone. But a study was published in 2019 which seems to back up the findings of the TS study.

Probiotics and social stressors

Published in the American Journal of Gastroenterology, researchers evaluated again the impact of B. Longum 1714 on mental health, with the focus this time being social stress. In the study, which was placebo controlled and double blinded, those administered B. Longum 1714 showed less stress and greater resiliency in response to a social isolation / rejection simulation designed to induce stress. Improved performance was confirmed using brain imaging.

To quote the study authors:

During the resting state, B. longum 1714™ induced an increase in theta band power in the frontal and cingulate cortex and a decrease in beta-3 band power in the fusiform cortex, hippocampus, temporal cortex, and cerebellum. Although no significant change of SF36 was noted after the 4-week probiotic intake, the increase in theta band and decrease in beta-3 band power found in the resting state was associated with increase in perceived energy/vitality levels, as assessed by the SF36.

Closing thoughts

It is well established that the gut and brain communicate. Through what is known as the “enteric nervous system,” our digestive health impacts on our mental health. Although the exact mechanisms are yet to be teased out, it isn’t a complete shock that certain strains of bacteria, such as B. Longum, can reduce stress and boost mood in humans. 3

Jennifer Nguyen

Jennifer Nguyen is a scientist living in San Diego. She did her training in molecular immunology, with a focus on checkpoint proteins and their role in autoimmune disease. She now works in cancer immunology and microbiome research. Jennifer spends her time away from the lab hanging out with her dog, climbing, and practicing yoga.

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