A Community in Transition
The gut microbiome undergoes significant compositional shifts with advancing age. After the relative stability of adulthood (roughly 20 to 65 years), older adults show progressive changes: declining alpha diversity, reduced abundance of butyrate-producing Firmicutes (particularly Faecalibacterium and Roseburia), and increased proportions of Proteobacteria and facultative anaerobes. These changes are not uniform — they vary with diet, medication burden, physical activity, living situation (community-dwelling vs institutional care), and geographic origin.
Inflammageing: The Immune Connection
Ageing is associated with a chronic, low-grade inflammatory state termed "inflammageing" — characterised by elevated circulating IL-6, TNF-α, and CRP without an identifiable acute cause. The ageing microbiome contributes to this process: reduced SCFA production impairs regulatory T cell differentiation, increased intestinal permeability permits greater microbial antigen translocation, and pro-inflammatory taxa expansion drives innate immune activation. This creates a feed-forward cycle where the ageing immune system promotes microbial dysbiosis, and microbial dysbiosis accelerates immune ageing.
Institutional Care and the Microbiome
A striking finding from the ELDERMET study was that microbial diversity correlated more strongly with living situation than with chronological age. Community-dwelling older adults maintained higher diversity than age-matched individuals in long-term residential care, where limited dietary variety, reduced physical activity, and increased antibiotic exposure converge to impoverish the microbiome. Microbiome diversity, in turn, correlated with frailty scores and inflammatory markers — suggesting that the institutional microbiome is both a marker and potential mediator of health decline.
Lessons from Centenarians
Centenarians — individuals who survive beyond 100 — show distinctive microbiome features that challenge the narrative of inevitable age-related decline. Studies from Japan, Italy, and China have identified that centenarian microbiomes often harbour increased abundance of Akkermansia and unique secondary bile acid-producing bacteria, alongside maintained microbial diversity. A 2023 Nature Aging study found that centenarian-enriched Bacteroides species produced isoallo-lithocholic acid — a secondary bile acid with potent anti-inflammatory and antimicrobial properties. Whether these microbial features contribute to longevity or merely accompany it remains under investigation.
Practical Strategies
Maintaining microbial diversity in older age centres on modifiable factors: dietary variety (emphasising fibre from diverse plant sources), regular physical activity (even light activity preserves diversity better than sedentary behaviour), appropriate medication review (minimising unnecessary PPIs and antibiotics), social engagement (community living supports dietary diversity), and possibly targeted prebiotic supplementation. Frailty-specific probiotic trials are ongoing, with early results suggesting that specific Bifidobacterium and Lactobacillus strains may improve inflammatory markers in frail elderly populations.