The microbiome refers to the vast community of microorganisms, bacteria, viruses, fungi and other microbes, that live in and on the human body. These microbes are most densely concentrated in the gut, particularly in the colon, but they also inhabit the skin, lungs, mouth and other mucosal surfaces.
Far from being passive passengers, these microbes play an active role in digestion, immunity, metabolism and even brain function. A balanced and diverse microbiome is considered a key pillar of healthspan and longevity.
Composition and diversity
Each person’s microbiome is unique, shaped by genetics, early life exposure, diet, lifestyle and environment. The gut microbiome alone consists of trillions of microbes, including over 1,000 species of bacteria that coexist in a delicate balance.
The composition varies across body regions:
- Gut microbiome: the most complex and influential;
- Oral and skin microbiome: protect against pathogens and support immune surveillance;
- Lung and vaginal microbiomes: play roles in respiratory and reproductive health-
Microbial diversity, the richness and balance of different species, is considered a marker of a healthy microbiome. Low diversity is linked to greater vulnerability to infections, inflammation and chronic disease.
Functions of the microbiome
It serves as an extension of the human body, performing metabolic and regulatory functions that we cannot do alone:
- Digestion and nutrient absorption: helps break down complex carbohydrates, fibers and proteins; supports the assimilation of nutrients;
- Production of key compounds: synthesizes vitamin K, B vitamins and short chain fatty acids (SCFAs) like butyrate, which fuel gut cells and regulate inflammation;
- Immune modulation: trains the immune system to distinguish between threats and harmless antigens, preventing overreactions and autoimmune responses;
- Gut brain communication: through the gut brain axis, the microbiome influences mood, stress response and cognitive performance via neurotransmitter production and vagus nerve signaling.
It also plays a defensive role, competing with pathogens for space and resources and producing antimicrobial compounds.
Microbiome and aging
As we age, it tends to lose diversity and become more imbalanced, a state known as dysbiosis. This shift is linked to:
- Increased intestinal permeability (“leaky gut”);
- Chronic low-grade inflammation (inflammaging);
- Declining immune function;
- Reduced nutrient synthesis and absorption;
- Greater susceptibility to infections, frailty and metabolic disorders.
Changes in microbiome composition have also been observed in age related diseases like type 2 diabetes, cardiovascular disease, Alzheimer’s and osteoporosis. Supporting it is increasingly viewed as a strategy to slow biological aging and preserve function.
The human microbiome is a complex and dynamic ecosystem that plays a central role in maintaining health, energy, mood and longevity. As we age, protecting and nurturing this microbial community becomes essential for preserving resilience, digestion, immunity and even cognitive performance.
