The closer scientists look at the bacteria in the gut, the clearer its importance to our overall health becomes, and new research links a particular type of gut microbiome development with longer lifespans and a healthier old age.
In a study of more than 9,000 people across three different cohorts, new research has found that our gut microbiomes become more unique and personalised to us as we get older, and that the number of core bacteria (such as Bacteroides) tend to decrease as well.
This pattern seems to be associated with physical health and longevity as well. So people whose microbiomes aren't continuing to change in old age, and which aren't seeing a reduction in core bacteria, tend not to be as healthy or to live as long.
"This uniqueness signature can predict patient survival in the latest decades of life," says biochemist Tomasz Wilmanski, from the Institute for Systems Biology (ISB).
"Interestingly, this uniqueness pattern appears to start in mid-life – 40-50 years old – and is associated with a clear blood metabolomic signature, suggesting that these microbiome changes may not simply be diagnostic of healthy ageing, but that they may also contribute directly to health as we age."
It was notable that even as microbiomes diverged in design at older ages, the metabolic functions they were carrying out were consistent across individuals – the researchers found certain metabolites linked to longevity in the guts of people (and various animals) whose microbiomes were following a healthier pattern.
As Wilmanski points out, the question remains whether these shifts in microbiome make-up are actually contributing to good health or only reflecting it, but it's certainly worthy of further investigation, the scientists say – and it adds some clarity to an area of research where findings haven't always been clear-cut.
For example, metabolites called indoles were discovered that have been previously linked to reduced inflammation in the guts of mice – and chronic inflammation is one of the health issues that are known to increase the risk of mortality in older people.
"Prior results in microbiome-ageing research appear inconsistent, with some reports showing a decline in core gut genera in centenarian populations, while others show relative stability of the microbiome up until the onset of aging-related declines in health," says microbiologist Sean Gibbons, from ISB.
"Our work, which is the first to incorporate a detailed analysis of health and survival, may resolve these inconsistencies."
While the study as a whole covered people aged from 18 to 101, it was a particular cohort of individuals aged between 78 and 98 that enabled the researchers to take a close look at how microbiomes and mortality might be linked.
We know that it's at the start and the end of our lives when our gut bacteria mix goes through the biggest changes, and this latest study backs up the idea that a continually evolving belly bacteria mix late in life is a good sign: It's perhaps an indicator of a still thriving body into the latter years of life.
The study suggests that a healthy gut microbiome – whatever that is – may not look the same at different stages of life, and that's a useful avenue for future research to explore. It looks as though our microbiomes can develop in different ways in elderly people, and some of those developments might be healthier than others.
"This is exciting work that we think will have major clinical implications for monitoring and modifying gut microbiome health throughout a person's life," says bioengineer Nathan Price, from ISB.
The research has been published in Nature Metabolism.