Age-Related Cognitive Decline, Focus on Microbiome: A Systematic Review and Meta-Analysis

Abstract

Aging is a complex process influenced by genetics and the environment, leading to physiological decline and increased susceptibility to diseases. Cognitive decline is a prominent feature of aging, with implications for different neurodegenerative disorders. The gut microbiome has gained attention for its potential impact on health and disease, including cognitive function. This systematic review and meta-analysis aimed to investigate the relationship between the gut microbiome and cognitive function in the context of aging. Following PRISMA guidelines, a comprehensive search strategy was employed in PubMed, Scopus, and Web of Science databases. Studies exploring the role of the microbiome in cognition and neurodegenerative disorders, published between 2013 and 2023, were included. Data extraction and quality assessment were performed. Quantitative synthesis using statistical analyses was performed to examine microbial diversity and relative abundance in various cognitive conditions. Sixteen studies involving a total of 1303 participants were included in the analysis. The gut microbiota’s relative abundance was different in individuals with cognitive impairments such as Alzheimer’s disease, Parkinson’s disease, and dementia, compared to the healthy controls. The most prevalent phyla affected were Firmicutes, Bacteroidetes, Actinobacteria, and Proteobacteria. Meta-analyses indicated substantial heterogeneity among studies focusing on Alzheimer’s disease. The overall quality of evidence related to microbial analysis was moderate. The gut microbiome’s role in cognitive decline and neurodegenerative disorders warrants investigation. Altered microbial abundance, particularly in specific phyla, is associated with cognitive impairments. However, variations in study findings and methodologies highlight the complexity of the relationship between the gut microbiome and cognitive function. Further studies are needed to better understand the mechanisms underlying this connection and its potential implications for aging and cognitive health.

Exploring the Influence of Gut–Brain Axis Modulation on Cognitive Health: A Comprehensive Review of Prebiotics, Probiotics, and Symbiotics

“…During aging, the composition of the microbiome may change, influencing cognitive health [ 51 , 52 ]. As time progresses, microbiome diversity may decrease, potentially due to aging processes and cognitive decline [ 4 , 53 , 54 ]. Additionally, inflammatory processes may become more prevalent during aging [ 55 ], potentially harming brain structures and functions, indicating a bidirectional relationship.…”

Assessing Risk Factors for Cognitive Decline Using Electronic Health Records: A Scoping Review

“…Fourth, there are considerable opportunities to investigate additional risk or protective factors that non-EHR studies have identified but were overlooked in the reviewed articles, including genetic markers (e.g., apolipoprotein E, presenilin 1 and 2, and amyloid precursor protein), 99 environmental toxins (e.g., lead, pesticides), 100 mild traumatic brain injury, 101 endocrine factors (such as hypothyroidism), sleep disturbance (like sleep apnea or chronic sleep deprivation), 8, 102 bilingualism, 103 vitamin and nutritional deficiencies, 104 and the microbiome (e.g., gut microbiome). 105 Fifth, while the existing literature primary focuses on dementia or AD, fewer studies address the early onset of AD and the initial stages of cognitive decline, such as mild cognitive impairment and subjective cognitive decline. Sixth, almost all the reviewed articles have used data from structured fields of the EHR.…”

Platelet Dynamics in Neurodegenerative Disorders: Investigating the Role of Platelets in Neurological Pathology

“…This necessity has led researchers to shift their focus from the central nervous system (CNS) to other body systems, such as peripheral blood, in the study of neurodegenerative disorders [14]. Although neurocognitive conditions have traditionally been identified as pathologies affecting the neuronal sphere, with all studies and diagnoses focused on the CNS, the past few years have seen a shift from this neuro-centric vision [15,16]. Evidence revealed that the characteristic hallmarks of pathologies affecting neuronal cells can be identified in both neurons and peripheric cells [17][18][19][20][21] and that also other systems, outside the CNS, take part in the pathogenic process of neurocognitive disorders.…”