Can your gut microbiome influence how long you live?

People who live to a very old age often have a strikingly different gut microbiome from that of younger elderly people. In people aged 105 and older, bacterial groups such as Akkermansia and Bifidobacterium are more strongly represented than in 'ordinary' octogenarians or centenarians. Whether these bacteria bring about extreme old age or simply go along with it has not been proven. These are small observational studies.

A larger study, involving more than 9,000 people, reveals another interesting pattern. People older than around 80 whose gut microbiome becomes increasingly unique compared to that of others have a better chance of survival over four years. People who, at an advanced age, still had a fairly 'standard' gut microbiome with large amounts of the common Bacteroides bacteria were actually less likely to survive those four years. Again, this is an association, not proof of cause and effect.

Multiple studies have consistently found that a diverse gut microbiome containing bacteria that produce anti-inflammatory compounds is associated with healthy ageing. The very oldest people also appear to have a greater capacity in their gut microbiome for producing butyrate, a fatty acid that is beneficial for the gut wall and for dampening inflammation. This pattern emerges in studies from different countries and cultures, which makes it more credible, but causality remains unproven.

How the gut microbiome might influence lifespan is still being actively investigated. Ideas centre on a stronger gut barrier, less chronic low-grade inflammation (which normally increases with age), and better functioning of the energy-producing organelles in cells. These are biologically plausible pathways, but most of the evidence for them still comes from laboratory and animal research, not from large experiments in humans.

A serious limitation of this entire field of research is that there is no universally accepted definition of what a 'healthy' gut microbiome actually is. Diet, lifestyle, medication use and genetics all influence the gut microbiome. This makes it very difficult to rule out the possibility that healthy people happen to also have a healthier gut microbiome, rather than the other way around. Recommendations that promise to 'optimise' your gut microbiome for a longer life therefore currently go beyond the available evidence.