A High Level Overview of Gut Microbiota in the Context of Aging
There is an increasing level of interest in how and why the composition of microbes in the gut changes with age, and how and why those changes affect health. It is not unreasonable to argue that these effects are in the same ballpark of significance as, say, exercise. Short-lived species, that tend to exhibit sizable effects on health and life span as a result interventions that impact aspects of aging, do appear to show a slower pace of aging as a result of engineering the gut microbiota to be more youthful in character. Gut microbes at the very least interact strongly with the immune system, but there is clearly a lot more than that going on under the hood.
The human digestive tract is inhabited by numerous microorganisms. Bacteria outnumber all other members of the gut microbial community, and the total number of bacterial species found in the gut is estimated to be about 500-1,000. The most populous bacterial phyla, constituting more than 90% of the gut microbiota are Bacteriodetes and Firmicutes. The remainder consists of many species in other phyla in lower abundance, some of which may provide important metabolites and functions for healthy aging.
Individual gut microbiotas show distinct profiles, and this inter-individual variation is greater in older adults. Longitudinally, however, gut microbiotas of healthy adults are relatively stable even for decades. Thus, once established early in life (even within 3 years after birth), the gut microbiota seems to be rather stably maintained. Nevertheless, it is responsive to the host's dietary and health conditions, much as the host's epigenome is to various environmental cues. In fact, the gut microbiota interfaces the gut environment with the epigenome, but its communication with the host systems involves various signaling networks and their mediators. For instance, the "gut-brain axis" connects the gut microbiome with the central nervous system via neurons, hormones, or cytokines.
Despite variation between individuals, most adult age groups, from young to extremely old, seem to possess a common core function in their microbiomes that is provided by members of abundant taxa. If so, what is important in the gut microbiota for healthy aging could be a compositional change in the functional core microbiome or an enrichment of non-core functions with advancing age.
With advancing chronological age, the gut microbiota becomes more diverse. However, when biological age is considered with adjustment for chronological age, overall richness decreases, while certain bacterial taxa associated with unhealthy aging thrive. Thus, as biological age increases, the homeostatic relationship between the gut microbiota and the host deteriorates, while gut dysbiosis increases. These dysbiotic changes in the aging gut can negate the beneficial effects of the gut microbiome on the nutrient signaling pathways, and provoke proinflammatory innate immunity and other pathological conditions.
Bravo for including this important issue here. I know this isn't health advice site, but still, I think it should be said: A majority of Americans have a systematic yeast infection from too much simple sugars in their diet, and this affects the gut microbiome. Equaling bad, there is long term and even permanent buildup of septic material in the lower gut, continuously poisoning people and creating a bad environment for good flora. If everyone would eat less sugar, cleanse their guts, and reboot their gut microbiome with probiotics, I'll go so far as to say we could cut the ~$3 Trillion spent on sick care every year in half.
To me it seems that the aging body is promoting the change in the bacterial mix, which can rainforest the bad state. Many people have imbalanced gut flora after using antibiotics and sometimes all it takes to fix the issue is taking a few pills with the right bacteria or Ebenezer eating yogurt. If the environment is skewed out would territories a constant insertion of the desired bacterial culture. I think unbalanced fit bacteria can trigger or exacerbate the lactose intolerance.
But I doubt we can find something that significantly alters the aging process.