Probiotics for Depression: Can They Help?

clinical-trial PMID: 31078831

Quick Summary: A study found that taking probiotics daily might help reduce some symptoms of depression, particularly in people with milder cases. The probiotics seemed to improve how people reacted to negative thoughts.

Can Probiotics Help With Depression?

This research looked at whether taking probiotics could help people with depression. The study found that people taking a specific probiotic supplement showed a significant improvement in their cognitive reactivity. Cognitive reactivity is how easily someone gets caught up in negative thoughts, which can make depression worse.

What The Research Found

Probiotics and Cognitive Reactivity: People taking probiotics had a greater reduction in cognitive reactivity compared to those taking a placebo (a sugar pill).

Mild to Moderate Depression: The positive effect on cognitive reactivity was more noticeable in people with milder forms of depression.

No Change in Gut Bacteria: The probiotics didn't significantly change the types of bacteria in the gut.

Study Details

Who was studied: 71 adults with mild to severe depression.

How long: The study lasted for 8 weeks.

What they took: Participants took either a daily probiotic supplement (Ecologic® Barrier) or a placebo (a pill with no active ingredients).

What This Means For You

Potential Benefit: If you have mild to moderate depression, taking probiotics might help you manage negative thoughts.

Not a Cure: Probiotics are not a guaranteed cure for depression, and this study is just one piece of the puzzle.

Talk to Your Doctor: Always talk to your doctor before starting any new supplements, especially if you're already taking medication for depression.

Study Limitations

Not Everyone Finished: A lot of people dropped out of the study, which could affect the results.

More Research Needed: The study was relatively short, and more research is needed to confirm these findings and understand how probiotics work.

Specific Probiotic: The study used a specific type of probiotic (Ecologic® Barrier). Other probiotics might not have the same effect.

Key Findings

The study found that daily probiotic supplementation (Ecologic® Barrier) significantly reduced cognitive reactivity—a vulnerability marker for depression—compared to placebo, particularly in participants with mild to moderate depression. However, probiotics did not alter gut microbiota composition. A correlation between Ruminococcus gnavus abundance and higher depression scores was observed, suggesting potential microbial associations.

Study Design

This was a randomized, triple-blind, placebo-controlled clinical trial conducted over 8 weeks. The sample included 71 adults with mild to severe depression (DSM-5 criteria), randomized to probiotic (n=34) or placebo (n=37). A non-depressed control group (n=20) was also assessed for baseline comparisons. Weekly monitoring visits were conducted, and outcomes included changes in depressive symptoms (PHQ-9), cognitive reactivity (Leiden index), and gut microbiota analysis via 16S rRNA sequencing.

Dosage & Administration

Participants consumed one sachet daily of either Ecologic® Barrier (containing 10 bacterial strains, total 5 billion CFU) or a visually identical placebo, dissolved in water. Compliance was monitored via returned packaging.

Results & Efficacy

Cognitive Reactivity: Probiotic group showed a mean decrease of 3.4 vs. 0.9 in placebo (p=0.04, d=0.43). In mild/moderate depression subgroup (n=50), the reduction was 4.3 vs. 0.6 (p=0.007, d=0.71).
Depressive Symptoms: No significant between-group differences in PHQ-9 scores (p=0.12), though both groups improved due to non-specific effects of weekly monitoring.
Microbiota: No significant changes in alpha/beta diversity or probiotic-targeted taxa. Ruminococcus gnavus correlated with higher PHQ-9 scores (p=0.03, R²=0.11).

Limitations

High Attrition: 27 participants (38%) dropped out, potentially biasing results.
Microbiota Analysis: 16S sequencing may lack sensitivity to detect subtle strain-level changes; shotgun metagenomics could yield more insights.
Short Duration: 8 weeks may be insufficient to assess long-term microbiota or mood effects.
Uncontrolled Variables: Diet, medication, and lifestyle factors were not standardized.

Clinical Relevance

The probiotic Ecologic® Barrier may reduce cognitive reactivity—a key psychological risk factor for depression relapse—especially in mild/moderate cases. While the microbiota composition remained unchanged, the psychological benefits suggest probiotics could act via mechanisms like immune modulation or metabolite production. Users should note that effects may depend on strain specificity and monitoring frequency. Further research is needed to confirm these findings in larger cohorts and explore probiotics as adjuncts to standard depression therapies.

Source: PubMed (2019)