Abstract
Aging is determined by complex interactions among genetic and environmental factors. Increasing evidence suggests that the gut microbiome lies at the core of many age-associated changes, including immune system dysregulation and susceptibility to diseases. The gut microbiota undergoes extensive changes across the lifespan, and age-related processes may influence the gut microbiota and its related metabolic alterations. The aim of this systematic review was to summarize the current literature on aging-associated alterations in diversity, composition, and functional features of the gut microbiota. We identified 27 empirical human studies of normal and successful aging suitable for inclusion. Alpha diversity of microbial taxa, functional pathways, and metabolites was higher in older adults, particularly among the oldest-old adults, compared to younger individuals. Beta diversity distances significantly differed across various developmental stages and were different even between oldest-old and younger-old adults. Differences in taxonomic composition and functional potential varied across studies, but Akkermansia was most consistently reported to be relatively more abundant with aging, whereas Faecalibacterium, Bacteroidaceae, and Lachnospiraceae were relatively reduced. Older adults have reduced pathways related to carbohydrate metabolism and amino acid synthesis; however, oldest-old adults exhibited functional differences that distinguished their microbiota from that of young-old adults, such as greater potential for short-chain fatty acid production and increased butyrate derivatives. Although a definitive interpretation is limited by the cross-sectional design of published reports, we integrated findings of microbial composition and downstream functional pathways and metabolites, offering possible explanations regarding age-related processes.
Highlights
Aging refers to the process of becoming older, a process that is genetically determined and environmentally modulated [1]
We assessed the relevance of gut microbiota composition to the phenomenon of aging and found long-lived individuals, (B) changes and transition in gut the studies fell into four categories with broad focus on: (A) the gut microbiota composition of microbiota that accompany aging across the lifespan, (C) relationship of the gut microbiota to cognition in extremely long-lived individuals, (B) changes and transition older adults, and (D) changes to the gut microbiota following interventions targeting the microbiome in in gut microbiota that accompany aging across the lifespan, (C) relationship of the gut microbiota to older adults
Detailed sample cognition in older adults, and (D) changes to the gut microbiota following interventions targeting the and methodology characteristics for each study are provided in supplementary Table S1 and S2, microbiome in older adults
Summary
Aging refers to the process of becoming older, a process that is genetically determined and environmentally modulated [1]. It involves changes in dynamics of biological, environmental, behavioral, and social processes. The microbiome is a principal factor in determining the immune system response and its dysregulation may sustain pro-inflammatory states [5]. Age-related changes in pro-inflammatory status result in low-level systemic inflammation (“inflammaging”) that increases the propensity for chronic diseases and disabilities, including cardiovascular disease, cognitive decline, metabolic disease, frailty, and mortality [7,8]. Gut microbes can communicate with the brain and modulate behavior, including higher-order cognitive functions, via the “gut–brain axis” through neural, immune, and hormonal mediators [9]. The microbiome offers an exciting perspective to understanding both physical and cognitive aspects of aging
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