Probiotic supplementation demonstrates therapeutic potential in treating gut dysbiosis and improving neurocognitive function in age-related dementia

• Published in: European journal of nutrition Vol. 61; no. 4; pp. 1701 - 1734
• Main Authors: Meng, Henry Yue Hong, Mak, Christopher Chi Hang, Mak, Wing Yan, Zuo, Tao, Ko, Ho, Chan, Francis Ka Leung
• Format: Journal Article
• Language: English
• Published: Berlin/Heidelberg Springer Berlin Heidelberg 01-06-2022; Springer Nature B.V
• Subjects: Age; Alzheimer's disease; Biomarkers; Chemistry; Chemistry and Materials Science; Cognition; Dementia; Dementia disorders; Dietary supplements; Digestive system; Dysbacteriosis; Gastrointestinal tract; Inflammation; Intestinal microflora; Microbiomes; Neurodegeneration; Neurodegenerative diseases; Neuromodulation; Nutrition; Probiotics; Review; Supplements; Gut microbiota; Probiotics; Microbiota–gut–brain axis; Neurodegeneration; Ageing
• ISSN: 1436-6207; 1436-6215
• DOI: 10.1007/s00394-021-02760-4

Purpose
Probiotics, as live microorganisms that improve intestinal microbial balance, have been implicated in the modulation of neurodegenerative diseases via the microbiome–gut–brain axis by improving gut dysbiosis. This review examines the association between probiotics and neurocognitive function in age-related dementia.
Methods
We searched MEDLINE, Embase, Scopus, Web of Science and Cochrane library for in vivo studies using equivalent combinations of “probiotics” and “dementia” as per PRISMA. From the 52 in vivo studies identified, 5 human and 22 animal studies with comparable quantitative outcomes on neurocognitive/behavioural function were meta-analysed by forest plots, subgroup analysis and meta-regression. The analysis of biomarkers, risk of bias and publication bias were also performed.
Results
In elderly humans, probiotics correlates with a non-significant difference of neurocognitive function in Mini-Mental State Examination, but with significant improvement only in those diagnosed with Alzheimer’s disease. In animals, probiotics significantly improved neurocognitive function as measured by Morris Water Maze, Y-Maze, and Passive Avoidance. Further analysis by subgrouping and meta-regression found that the probiotics-neurodegeneration association is age dependent in humans but is neither dose dependent nor duration dependent in animals or humans. Analysis of biomarkers suggested that the neurocognitive effect of probiotics is associated with an altered gut microbiome profile, downregulated proteinopathic, inflammatory and autophagic pathways, and upregulated anti-oxidative, neurotrophic, and cholinergic pathways.
Conclusion
Overall, we report promising results in animal studies but limited evidence of probiotics leading to neurocognitive improvement in humans. More research into probiotics should be conducted, especially on live biotherapeutic products for targeted treatment of gut dysbiosis and age-related dementia.