Can your microbiome reveal how old you are biologically?

The gut microbiome changes systematically with age, but in healthy older adults it does so in a specific way: it becomes increasingly personal. An analysis of more than 9,000 people showed that from middle age onward the microbiome develops unique characteristics that diverge further and further from one person to the next. Healthy people in their eighties and nineties displayed this personal shift; less healthy peers did not. People who at an advanced age still had a strong dominance of the bacterial group Bacteroides (a sign of little individuality in the microbiome) had a lower chance of survival over the following four years, consistently across three independent groups.

In addition, microbially produced compounds in the blood, amino acid derivatives, were strongly associated with this microbiome uniqueness. That pattern also ran parallel with a blood-protein profile of 22 proteins that predicts ageing and the risk of cardiovascular disease and diabetes. This link between the microbiome and blood proteins was found in a longitudinal study of nearly 3,800 people over 9 years, and the researchers estimated the microbiome to be a modifiable factor in that relationship. Definitive proof that you can steer your biological age through the microbiome is, however, still lacking.

Mouse studies add a mechanistic layer. Mice with a hereditary accelerated-ageing disease had a disrupted microbiome, and a faecal transplant from healthy mice extended both their healthspan and their lifespan. Even a single specific bacterium, Akkermansia, already proved sufficient to produce this effect. In people aged 100 or older, higher levels of this type of bacterium were found. These animal results are interesting, but translation to healthy humans remains uncertain.

A practical caveat: there is no such thing as 'the' standard microbiome. More than 150,000 microbiome genomes show that populations outside the Western world have 40% more unique bacterial species, and 77% of the species found were absent from existing databases. A microbiome test that measures your biological age is therefore not yet a clinically validated tool, even though the associations with survival and ageing are statistically robust.