Can probiotics (Probiotic Bacteria) support brain health?

Probiotics for Brain Health

Current evidence does not support routine probiotic supplementation for brain health in healthy adults, though specific strains may benefit older adults with mild cognitive impairment or suspected dementia. 1, 2

Evidence-Based Recommendations by Population

Healthy Adults

• Do not routinely recommend probiotics for cognitive enhancement in healthy young to middle-aged adults 3
• A high-quality 2022 RCT (N=59, mean age 27 years) using Vivomixx® multi-strain probiotic for 4 weeks showed no changes in hippocampal volume, functional connectivity, cognitive performance, or mental health outcomes 3
• Bayesian analysis in this study provided strong evidence favoring the null hypothesis 3

Older Adults with Cognitive Impairment

Consider specific probiotic strains for older adults (≥65 years) with mild cognitive impairment or suspected dementia, using a 12-16 week trial period 2, 4

Strain-Specific Evidence:

• Bifidobacterium breve A1 (2×10¹⁰ CFU daily for 16 weeks) significantly improved RBANS total score by 11.3 points (95% CI 6.7-15.8, p<0.0001) in 80 older adults with suspected MCI, with particular improvements in immediate memory, visuospatial/constructional abilities, and delayed memory 4

• Bifidobacterium bifidum BGN4 + Bifidobacterium longum BORI (12 weeks) improved mental flexibility and reduced stress scores in 63 healthy elders (≥65 years), while increasing serum BDNF levels and reducing inflammation-causing gut bacteria 5

• Multi-strain containing B. longum, L. helveticus, and L. plantarum (4 weeks) altered gray matter volume in the left supramarginal gyrus and superior parietal lobule, with functional connectivity changes in default mode, salience, and frontoparietal networks in 22 healthy subjects 6

Systematic Review Findings

• 9 of 10 RCTs in older adults (with AD, MCI, or healthy cognition) showed significant cognitive improvement after probiotic supplementation compared to controls 2
• The single negative study involved severe AD patients, suggesting probiotics may be ineffective in advanced dementia 2
• Optimal treatment duration appears to be 12-24 weeks 2

Critical Limitations and Caveats

Strain Specificity is Paramount

• Benefits demonstrated for one probiotic strain cannot be extrapolated to other strains or species 1, 7
• No single strain possesses all known probiotic benefits 1
• The probiotic market is relatively unregulated, with claims often inappropriately transferred between products 1

Insufficient Evidence Areas

• Depression and mental health disorders lack sufficient quality evidence to recommend probiotics 1, 8
• Metabolic diseases require more well-conducted studies 1
• The 2017 meta-analysis on depression (5 trials, 365 participants) showed reduced depression scores (MD -0.30,95% CI -0.51 to -0.09, p=0.005), but this evidence is not considered strong enough for routine recommendation 8

Practical Clinical Algorithm

For patients inquiring about probiotics for brain health:

1. Age <65 years with normal cognition: Do not recommend probiotics for cognitive enhancement 3

2. Age ≥65 years with suspected MCI or mild dementia:

   • Consider Bifidobacterium breve A1 2×10¹⁰ CFU daily for 16 weeks 4
   • Alternative: B. bifidum BGN4 + B. longum BORI for 12 weeks 5
   • Assess cognitive function at baseline and 12-16 weeks using validated tools (RBANS, MMSE) 4

3. Severe dementia: Do not recommend probiotics (no demonstrated benefit) 2

4. Immunocompromised patients: Probiotics are absolutely contraindicated due to bacteremia risk 7

Mechanism Considerations

• Probiotics may work through the microbiome-gut-brain axis by reducing inflammation-causing gut bacteria 5
• Changes in gut microbiota composition (particularly Eubacterium and Clostridiales) correlate negatively with serum BDNF levels 5
• Structural brain changes and altered functional connectivity in specific networks may mediate cognitive effects 6