Probiotic supplements are effective in people with cognitive impairment: a meta-analysis of randomized controlled trials

The impact of probiotics therapy on cognitive and metabolic characteristics in patients with cognitive impairment: An umbrella review of meta-analysis of randomized controlled trials

BACKGROUND

While existing meta-analysis suggest that probiotic therapies may enhance cognitive functions and influence metabolic characteristics, the findings have been inconclusive. In light of these discrepancies, our study undertakes an umbrella review to more precisely determine the aggregate effects and rigorously evaluate the credibility and quality of evidence.

METHODS

We conducted a systematic search across seven databases, including PubMed, Embase, the Cochrane Library, ProQuest, Web of Science, CINAHL, and Scopus, from their inception to June 20, 2024. We utilized the AMSTAR-2 tool to evaluate the quality of the meta-analyses and applied the GRADE system to rate the quality of the evidence. We estimated the final effect sizes (ESs) along with their 95% confidence intervals (CI) and performed both sensitivity and subgroup analyses to explore the sources of heterogeneity.

RESULTS

Among the 314 articles identified in our search, 13 meta-analysis that met the criteria were included in the study. The quality of the evidence in these studies was graded from high to very low. Our results demonstrate that probiotic treatment significantly enhances cognitive function in patients (ESSMD = 0.39, 95%CI: 0.19 to 0.59, p < 0.001). Moreover, probiotic treatment notably decreased level of serum malondialdehyde (MDA), insulin resistance as detected by homeostasis model assessment method (HOMA-IR) and high-sensitivity C-reactive protein (hs-CRP) (p < 0.001). Conversely, probiotic treatment did not significantly impact triglycerides and very-low-density lipoprotein (VLDL) in patients (p > 0.05).

CONCLUSION

Although preliminary evidence indicated that probiotic therapy may positively impact cognitive function, MDA, HOMA-IR, and hs-CRP, the overall quality of the existing evidence is insufficient to provide strong support. Therefore, future research must employ more rigorous designs or initiate larger clinical trials to produce more compelling evidence to further validate the efficacy of probiotic therapy on cognitive function of patients with cognitive dysfunction.

Efficacy of probiotics in patients with cognitive impairment: A systematic review and meta-analysis

OBJECTIVE

To conduct an in-depth exploration of the specific impacts of probiotics and prebiotic supplements on cognitive impairment, it is imperative to also investigate pertinent factors, including the optimal dosage of probiotics for enhancing cognitive function. This investigation is essential for optimizing probiotic interventions to prevent and treat cognitive decline, aimed at preventing and aiding in the treatment of cognitive decline among patients with cognitive impairment.

METHODS

A comprehensive computerized search was conducted across the Embase, PubMed, Web of Science, Cochrane Library, SinoMed, CNKI, Wanfang and WeiPu Data. Studies targeting randomized controlled trials (RCTs) were included. This search covered a timeframe extending from the inception of each database to September 2024. Following an independent process of literature screening, data extraction, and rigorous quality assessment conducted by two investigators, a meta-analysis was performed using Stata 15.0 software.

RESULTS

A total of ten studies, involving 778 patients, were included in the analysis. The meta-analysis revealed that probiotics were effective in enhancing cognitive function among patients with cognitive impairment, with a standardized mean difference (SMD) of 0.52 (95% CI: 0.07, 0.98; P < 0.001). Subgroup analysis further demonstrated that the largest effect size was observed for studies utilizing the Mini-Mental State Examination (MMSE) scale as the outcome measure (SMD = 0.88). Additionally, the greatest efficacy was associated with single-strain probiotics (SMD = 0.81), and interventions lasting ≤12 weeks exhibited the most pronounced effect (SMD = 0.61).

CONCLUSION

Probiotics have been shown to enhance cognitive function, with a probiotic intervention program featuring a single probiotic strain and a duration of ≤12 weeks demonstrating particularly robust efficacy in improving cognitive function, as assessed by the MMSE scale.

Effect of probiotics on cognitive function and cardiovascular risk factors in mild cognitive impairment and Alzheimer's disease: an umbrella meta-analysis

BACKGROUND

This umbrella meta-analysis evaluates the effects of probiotics on cognitive function and metabolic health in Alzheimer's disease (AD) and mild cognitive impairment (MCI) by synthesizing findings from meta-analyses of randomized controlled trials (RCTs), as existing evidence remains inconclusive.

METHODS

A systematic search was conducted in PubMed, Web of Science, and Scopus to identify meta-analyses of RCTs investigating the impact of probiotic supplementation on cognitive function and metabolic biomarkers. The random-effects model was used. Heterogeneity and publication bias were assessed.

RESULTS

Thirteen meta-analyses, comprising 3910 patients, were included. Probiotics significantly improved cognitive function in AD (SMD = 0.78, 95% CI: 0.33 to 1.23) and MCI (SMD = 0.43, 95% CI: 0.15 to 0.70). Probiotics also increased total antioxidant capacity (SMD = 0.40, 95% CI: 0.11 to 0.70) and reduced MDA (SMD =  - 0.35, 95% CI: - 0.62 to - 0.09) and hs-CRP (SMD =  - 0.59, 95% CI: - 0.87 to - 0.30). Insulin resistance improved, as reflected by decreased HOMA-IR (SMD =  - 0.34, 95% CI: - 0.43 to - 0.26). No significant effects were observed on glutathione, nitric oxide, or lipid profiles.

CONCLUSION

Probiotic supplementation appears to enhance cognitive function and metabolic parameters in individuals with MCI and AD, likely through mechanisms involving inflammation reduction, oxidative stress modulation, and improved insulin sensitivity. Further high-quality RCTs are required to validate these findings and determine optimal probiotic formulations.

The role of the intestinal microbiome in cognitive decline in patients with kidney disease

Cognitive decline is frequently seen in patients with chronic kidney disease (CKD). The causes of cognitive decline in these patients are likely to be multifactorial, including vascular disease, uraemic toxins, blood-brain barrier leakage, and metabolic and endocrine changes. Gut dysbiosis is common in patients with CKD and contributes to the increase in uraemic toxins. However, the gut microbiome modulates local and systemic levels of several metabolites such as short-chain fatty acids or derivatives of tryptophan metabolism, neurotransmitters, endocannabinoid-like mediators, bile acids, hormones such as glucagon-like peptide 1 (GLP1) or cholecystokinin (CCK). These factors can affect gut function, immunity, autonomic nervous system activity and various aspects of brain function. Key areas include blood-brain barrier integrity, nerve myelination and survival/proliferation, appetite, metabolism and thermoregulation, mood, anxiety and depression, stress and local inflammation. Alterations in the composition of the gut microbiota and the production of biologically active metabolites in patients with CKD are well documented and are favoured by low-fiber diets, elevated urea levels, sedentary lifestyles, slow stool transit times and polypharmacy. In turn, dysbiosis can modulate brain function and cognitive processes, as discussed in this review. Thus, the gut microbiome may contribute to alterations in cognition in patients with CKD and may be a target for therapeutic interventions using diet, prebiotics and probiotics.

Probiotics: A potential strategy for improving diabetes mellitus complicated with cognitive impairment

Diabetes mellitus (DM) is a common metabolic disease and one of the diseases with the highest number of complications at present. As the disease progresses, patients will gradually develop diabetes-related cognitive decline, mild cognitive impairment (MCI) or even dementia. The occurrence of diabetes-combined cognitive impairment undoubtedly imposes a heavy burden on patients and their families. Current research suggests that risk factors such as blood glucose levels, insulin resistance, oxidative stress and neuroinflammation have an important role in the development of diabetic cognitive impairment (DCI). With the development of technology and in-depth research, the relationship between the two-way communication between the gut and the brain has been gradually revealed, and more studies have found that the gut microbiota plays an important role in the development of DCI. This review explores the feasibility of probiotics as a potential strategy to assist in the improvement of DCI and its potential mechanisms from the perspective of the factors affecting DCI.

Effects of Probiotics on Neurodegenerative Disease-Related Symptoms and Systemic Inflammation: A Systematic Review

In recent years, probiotics, as a class of biologically active microorganisms, have increasingly attracted attention for their potential in treating neurodegenerative diseases (NDDs). To comprehensively assess the effects of probiotics on clinical symptoms and systemic inflammation regulation in various NDDs, this systematic review conducted a detailed search of the Cochrane Library, Embase, PubMed, and Web of Science databases, ultimately including 22 eligible randomized controlled trials (RCTs), with 4 RCTs for Alzheimer's Disease (AD), 10 RCTs for Parkinson's Disease (PD), 2 RCTs for Multiple Sclerosis (MS), and 2 RCTs for Mild Cognitive Impairment (MCI), and intervention durations ranging from 4 to 16 weeks. The comprehensive analysis indicates that probiotics help improve clinical symptoms related to NDDs, including gastrointestinal function, cognitive function, quality of life, and mental health. Additionally, probiotics generally have a positive effect on reducing systemic inflammation and enhancing antioxidant capacity in patients. In conclusion, existing evidence supports the promising potential of probiotics in treating NDDs. However, further large-scale, high-quality studies are needed to explore specific differences in efficacy among various probiotic strains, dosages, and modes of administration. Moreover, considering that lifestyle and dietary habits may modulate the effects of probiotics, these external factors should also be included in research considerations to gain a more comprehensive understanding of the mechanisms and application strategies of probiotics in NDDs treatment.

Therapeutic effects of probiotics on symptoms of depression in children and adolescents: a systematic review and meta-analysis

This meta-analysis aimed at investigating the therapeutic effects of probiotics against the symptoms of depression in children and adolescents as well as to identify the potential confounders. Following PRISMA guidelines, major databases were searched for randomized controlled trials focusing on effects of probiotics against the symptoms of depression in children and adolescents to analyze the effect size (ES) for primary outcomes (i.e., improvement in depressive symptoms) expressed as standardized mean difference (SMD) and odds ratios (ORs) for continuous and categorical variables, respectively, with 95% confidence interval (CI). Meta-analysis of five studies (692 participants, mean age = 7.33 years, treatment duration 8-104 weeks) demonstrated no significant improvement in depressive symptoms in subjects receiving probiotics (SMD = 0.04, 95% CI: -0.33 to 0.41, p = 0.84, five studies, 692 participants). Subgroup analysis also showed no significant improvement associated with probiotic use relative to controls in the subgroup of studies focusing on individuals diagnosed with neurodevelopmental disorders (SMD = -0.11, 95% CI: -0.73 to 0.51, p = 0.72, three studies, 452 participants) and that recruiting the general population (SMD = 0.24, 95% CI: -0.43 to 0.91, p = 0.48, two studies, 240 participants). However, high levels of heterogeneity were found in both our primary results (I2 = 77%, p = 0.001) and subgroup analyses for those with neurodevelopmental disorders (I2 = 84%, p = 0.002) and the general population (I2 = 79%, p = 0.03). The results did not support the use of probiotics for relieving depressive symptoms compared with controls in children and adolescents diagnosed with neurodevelopmental disorders or in the general population. Nevertheless, given the high level of heterogeneity across the included trials and a lack of studies focusing on those with diagnoses of anxiety or depression in the current meta-analysis, further large-scale clinical investigations are required to elucidate the therapeutic potential of probiotics against depressive symptoms in these populations, especially in those diagnosed with neurodevelopmental disorders or depression.

Probiotic Formulation for Patients With Bipolar or Schizophrenia Spectrum Disorder: A Double-Blind, Randomized Placebo-Controlled Trial

BACKGROUND AND HYPOTHESIS

Probiotic augmentation offers a promising treatment for bipolar disorder (BD) and schizophrenia spectrum disorder (SSD). By targeting microbiome deviations, they may improve both gut and brain health.

STUDY DESIGN

In this double-blind, randomized, placebo-controlled trial with the multi-strain probiotic formulation Ecologic BARRIER, we aimed to improve psychiatric and cognitive symptoms, intestinal permeability, and gastrointestinal symptoms in patients with BD or SSD. A total of 131 patients were randomized 1:1 to receive either the probiotic supplement (n = 67) or a placebo (n = 64) for 3 months, in addition to treatment-as-usual. The primary outcomes were symptom severity assessed by the Brief Psychiatric Rating Scale and cognitive functioning by the Brief Assessment of Cognition in Schizophrenia.

STUDY RESULTS

No significant effect of probiotics was observed on psychiatric symptoms, but borderline significant improvement was observed in the cognition category of verbal memory (Linear Mixed Model (LMM) 0.33; adjusted P = .059). Probiotics beneficially affected markers of intestinal permeability and inflammation, including zonulin (LMMserum = -18.40; adjusted P = .002; LMMfecal = -10.47; adjusted P = .014) and alpha-1 antitrypsin (LMM 9.26; adjusted P = .025). Indigestion complaints significantly decreased in male participants in the probiotics group (LMM = -0.70; adjusted P = .010). Adverse events were similar between groups.

CONCLUSIONS

Our study observed significant advantages of probiotics for gut health in BD and SSD, with excellent safety and tolerability. A borderline effect on verbal memory was also indicated. These results underscore the need for further research into microbiome-targeted interventions for patients with complex brain disorders.

The effect of probiotics on select cognitive domains in mild cognitive impairment and Alzheimer's disease: A systematic review and meta-analysis

Background

Mild cognitive impairment (MCI) and Alzheimer's disease (AD) are progressive neurodegenerative disorders, and probiotics may offer therapeutic benefits by modulating gut microbiota and reducing inflammation.

Objective

This study systematically evaluated the impact of probiotics on cognitive function in MCI and AD through a meta-analysis of randomized controlled trials (RCTs).

Methods

A systematic review and meta-analysis were performed following PRISMA 2020 guidelines. PubMed, Embase, EBSCO, and Cochrane databases were searched for RCTs (January 2000-January 2024) on probiotic interventions lasting 8-24 weeks. Cognitive outcomes included Mini-Mental State Examination (MMSE), Montreal Cognitive Assessment (MoCA), language, naming, visual-spatial, memory, and attention. Data were analyzed using R with a random-effects model to calculate pooled standardized mean differences (SMDs) with 95% confidence intervals (CIs). Risk of bias was rigorously assessed.

Results

Out of 2000 articles, 500 full texts were screened, and 10 studies were included. The meta-analysis showed varied effect sizes: MMSE (SMD: 0.28, 95%CI -0.35-0.91, p = 0.38), MoCA (SMD: 0.51, 95%CI -0.49-1.52, p = 0.33), language (SMD: -0.12, 95% CI -0.54-0.29, p = 0.56), naming (SMD: 0.02, 95%CI -0.69-0.74, p = 0.95), visual-spatial (SMD: 0.38, 95%CI -0.13-0.88, p = 0.14), memory (SMD: 0.20, 95%CI -0.15-0.55, p = 0.26), and attention (SMD: -0.07, 95%CI -0.44-0.30, p = 0.71). Positive SMDs suggest cognitive improvement, while non-significant negative SMDs indicate trends toward decline, inclined by probiotic strains, duration, and participant characteristics.

Conclusions

Probiotics did not significantly improve cognitive function in MCI and AD patients, with variability in effects across cognitive domains, suggesting the need for tailored interventions and future studies.

Potential Alzheimer's disease drug targets identified through microglial biology research

INTRODUCTION

Microglia, the primary immune cells in the brain, play multifaceted roles in Alzheimer's disease (AD). Microglia can potentially mitigate the pathological progression of AD by clearing amyloid beta (Aβ) deposits in the brain and through neurotrophic support. In contrast, disproportionate activation of microglial pro-inflammatory pathways, as well as excessive elimination of healthy synapses, can exacerbate neurodegeneration in AD. The challenge, therefore, lies in discerning the precise regulation of the contrasting microglial properties to harness their therapeutic potential in AD.

AREAS COVERED

This review examines the evidence relevant to the disease-modifying effects of microglial manipulators in AD preclinical models. The deleterious pro-inflammatory effects of microglia in AD can be ameliorated via direct suppression or indirectly through metabolic manipulation, epigenetic targeting, and modulation of the gut-brain axis. Furthermore, microglial clearance of Aβ deposits in AD can be enhanced via strategically targeting microglial membrane receptors, lysosomal functions, and metabolism.

EXPERT OPINION

Given the intricate and diverse nature of microglial responses throughout the course of AD, therapeutic interventions directed at microglia warrant a tactical approach. This could entail employing therapeutic regimens, which concomitantly suppress pro-inflammatory microglial responses while selectively enhancing Aβ phagocytosis.

Efficacy of Probiotic Supplements on Brain-Derived Neurotrophic Factor, Inflammatory Biomarkers, Oxidative Stress and Cognitive Function in Patients with Alzheimer's Dementia: A 12-Week Randomized, Double-Blind Active-Controlled Study

The role of neurotrophic factors, oxidative stress, and inflammation in the pathogenesis of Alzheimer's disease (AD) has been explored. Animal studies have reported the positive effects of probiotics on these factors. Some clinical studies also support the potential role of probiotics in improving cognitive function via the gut-brain axis in older adults. However, clinical experimental studies evaluating the efficacy of probiotics targeting the neurotrophic factors and inflammatory biomarkers, particularly among AD patients, remain very limited. In this randomized, double-blinded, active-controlled trial, we used multi-strain probiotic supplements, including Bifidobacterium longum subsp. infantis BLI-02, B. breve Bv-889, B. animalis subsp. lactis CP-9, B. bifidum VDD088, and Lactobacillus plantarum PL-02 as the intervention. Participants were divided into an active control group (received probiotic supplements containing 5 × 107 colony-forming units per day, CFU/day) and a treatment group (1 × 1010 CFU/day). Student's t test was applied as the main method of statistical analysis. After 12 weeks of intervention, the treatment group demonstrated a 36% increase in serum brain-derived neurotrophic factor (BDNF) (* p = 0.005), a reduction in IL-1β (* p = 0.041), and an increase in antioxidant superoxide dismutase (SOD) (* p = 0.012). No significant change was found in the active control group. A trend toward less cognitive deterioration was observed, but not statistically significant. In conclusion, this study presents evidence supporting the benefits of multi-strain probiotics in enhancing BDNF, ameliorating inflammation and oxidative stress in AD patients.

Deciphering psychobiotics' mechanism of action: bacterial extracellular vesicles in the spotlight

The intake of psychobiotic bacteria appears to be a promising adjunct to neuropsychiatric treatment, and their consumption may even be beneficial for healthy people in terms of mental functioning. The psychobiotics' mechanism of action is largely outlined by the gut-brain axis; however, it is not fully understood. Based on very recent studies, we provide compelling evidence to suggest a novel understanding of this mechanism: bacterial extracellular vesicles appear to mediate many known effects that psychobiotic bacteria exert on the brain. In this mini-review paper, we characterize the extracellular vesicles derived from psychobiotic bacteria to demonstrate that they can be absorbed from the gastrointestinal tract, penetrate to the brain, and carry the intracellular content to exert beneficial multidirectional action. Specifically, by regulating epigenetic factors, extracellular vesicles from psychobiotics appear to enhance expression of neurotrophic molecules, improve serotonergic neurotransmission, and likely supply astrocytes with glycolytic enzymes to favor neuroprotective mechanisms. As a result, some data suggest an antidepressant action of extracellular vesicles that originate even from taxonomically remote psychobiotic bacteria. As such, these extracellular vesicles may be regarded as postbiotics of potentially therapeutic application. The mini-review is enriched with illustrations to better introduce the complex nature of brain signaling mediated by bacterial extracellular vesicles and indicates knowledge gaps that require scientific exploration before further progress is made. In conclusion, bacterial extracellular vesicles appear to represent the missing piece of the puzzle in the mechanism of action of psychobiotics.

The role of gut microbiota on cognitive development in rodents: a meta-analysis

Cognitive function includes learning, remembering and using acquired information. Emerging studies indicate the correlation between microbiota and cognitive function. Higher abundance of a specific gut microbiota, such as Bacteroidetes may improve cognitive abilities. However, another study reported different result. These results suggest that further systematic analysis is required to determine the effect of the gut microbiota abundance on cognitive development. The aim of this study is to summarize the abundance of the specific gut microbiota and cognitive development using meta-analysis. PubMed, ScienceDirect, and Clinical-Key were used as data bases to perform the literature search. Phylum Bacteroidetes, and family Lactobacillaceae were more abundant in cognitive-behavioral enhancement (CBE), whereas Firmicutes, Proteobacteria, Actinobacteria, and family Ruminococcaceae were less abundant in CBE. Differences in gut microbiota abundance are influenced by differences in stage of cognitive dysfunction, intervention, and strain of gut microbiota.

Controlling the Impact of Helicobacter pylori-Related Hyperhomocysteinemia on Neurodegeneration

Helicobacter pylori infection consists a high global burden affecting more than 50% of the world’s population. It is implicated, beyond substantiated local gastric pathologies, i.e., peptic ulcers and gastric cancer, in the pathophysiology of several neurodegenerative disorders, mainly by inducing hyperhomocysteinemia-related brain cortical thinning (BCT). BCT has been advocated as a possible biomarker associated with neurodegenerative central nervous system disorders such as Alzheimer’s disease, Parkinson’s disease, multiple sclerosis, and/or glaucoma, termed as “ocular Alzheimer’s disease”. According to the infection hypothesis in relation to neurodegeneration, Helicobacter pylori as non-commensal gut microbiome has been advocated as trigger and/or mediator of neurodegenerative diseases, such as the development of Alzheimer’s disease. Among others, Helicobacter pylori-related inflammatory mediators, defensins, autophagy, vitamin D, dietary factors, role of probiotics, and some pathogenetic considerations including relevant involved genes are discussed within this opinion article. In conclusion, by controlling the impact of Helicobacter pylori-related hyperhomocysteinemia on neurodegenerative disorders might offer benefits, and additional research is warranted to clarify this crucial topic currently representing a major worldwide burden.