Researchers at the University of Hawaii at Manoa report that certain bacteria living in the human gut are linked to how quickly people age biologically. Some species went with slower aging and others with faster aging1. The study, published in the journal Scientific Reports, found that differences in gut bacteria accounted for about 15% of the variation in participants’ rates of biological aging12.
The finding is a link, not proof. The researchers stress that their study does not show the bacteria cause faster or slower aging1.
What happened
The team collected stool and blood samples from 123 adults across a wide range of ages1. They worked out which bacteria were present in each person’s gut, then compared that with blood-based markers used to estimate how fast the body is aging1.
That aging measure is not the same as a person’s age in years. It is designed to estimate how quickly aging-related changes are happening inside the body1. The specific measure the team used is called DunedinPACE, which ScienceDaily describes as a biomarker of the pace of biological aging12. A biomarker is something measurable in the body, here in blood, that is used as a sign of a process.
The makeup of the gut microbiome, the large community of microbes living in the digestive system, showed a notable link with DunedinPACE1. Two species stood out:
- Bifidobacterium adolescentis was among the microbes most strongly linked to slower biological aging1.
- Succinivibrio dextrinosolvens showed one of the strongest links to faster aging1.
Senior author Alika K. Maunakea of the university’s John A. Burns School of Medicine said the gut patterns were tied to aging measures even after accounting for how old people were1:
“We found that microbial patterns in the gut were significantly associated with molecular measures of aging, even independent of chronological age.”
How strong the evidence is
This is an observational study: the researchers looked at what was already in people’s guts and blood, rather than changing anything. Based on the published descriptions, it compared samples from the same people at one point in time1. A study like this can show that two things tend to appear together. It cannot show that one causes the other.
The researchers say this directly. Finding certain microbes in people who age more slowly does not necessarily mean those bacteria are responsible for slowing aging12. The reverse could also be true, or something else, such as diet or health, could shape both.
The “about 15%” figure also has a plain meaning. Gut bacteria differences explained roughly one-seventh of the spread in aging pace between people1. The rest of that spread was tied to other things the study does not describe in the coverage available.
The group of 123 adults is small for linking hundreds of possible bacteria to a health measure. The coverage available to Biohack does not report the participants’ exact ages, health status or diets, or how the analysis adjusted for them beyond age.
What it does not show yet
- It does not show that adding or removing any bacterium changes how fast someone ages. The researchers say further studies are needed to test whether deliberately changing the gut microbiome affects biological aging or long-term health1.
- It does not show any effect on disease, lifespan or how people feel or function. The outcome was a blood-based estimate of aging pace, not illness or death1.
- It did not test any diet, probiotic, supplement or treatment.
Maunakea called the work an early step1:
“This is an important early step toward understanding the gut microbiome’s relationship with healthy aging.”
Who is behind it
The study comes from the University of Hawaii at Manoa. Braden P. Kunihiro is the lead author, Alika K. Maunakea is the senior author, and Ruben Juarez is a co-author1. The coverage available to Biohack does not say who funded the study or whether any author has commercial ties.
The study included Native Hawaiian and Pacific Islander participants. These groups have historically had limited representation in research on aging and gut microbes12. Juarez said including them could help scientists study how social circumstances and environment leave lasting biological marks over a lifetime1.
Kunihiro pointed to why the gut interests aging researchers. Unlike age in years, the gut’s bacteria can change with diet, lifestyle and environment1:
“The gut microbiome is highly responsive to lifestyle, diet, environment and other everyday exposures.”
How it fits the field
The idea that gut microbes affect aging is old. More than a century ago, Elie Metchnikoff, often called the father of probiotics, proposed that eating lactic acid bacteria like those in yogurt could delay aging-related mental decline3.
Later research has documented how the gut changes with age. A 2021 overview reported that after about age 60 to 65, gut bacteria diversity generally starts to fall. It also described a drop in the number of Bifidobacteria strains3. That is the same broad group as the species the Hawaii team linked to slower aging, though the overview did not look at this specific measure. A University of Florida explainer also describes diversity dipping after 65 and falling more sharply by 804.
Studies of very old people have reported distinct gut patterns. People who reach 100 often have more diverse gut bacteria than younger peers4. A 2021 study led by the Institute for Systems Biology found that people over 80 with unusually high levels of Bacteroides bacteria had shorter lifespans4. Japanese centenarians with an average age of 107 were found to have gut microbes that make unusual bile acids, compounds that help digest fat3.
Like the new study, those human findings are associations. As the 2021 overview put it, none of these studies prove that gut bacteria caused people to live longer3. The closest thing to cause-and-effect evidence so far comes from animals. In a mouse study in Nature Aging, moving gut microbes from young mice into old mice through a stool transplant reduced some memory and learning problems. It also reversed some immune changes linked to aging3. Those were mouse results and have not been shown in people3.
The Hawaii study adds a different angle. Instead of comparing old with young people, or lifespan, it compared gut bacteria with a blood measure of aging speed in adults of many ages1.
What to watch next
- Repeat studies. Whether larger groups, in other populations, show the same link with the same bacterial species.
- Tracking over time. Whether people’s gut bacteria and aging pace move together when they are measured repeatedly over years.
- Tests of change. The researchers say future work should test whether deliberately changing the gut microbiome can affect biological aging, and clarify the mechanisms involved1.
For now, the study offers a measured link between specific gut microbes and one estimate of how fast the body ages. It leaves open whether those microbes play any part in the aging itself12.
