Key Takeaways
- In Danish adults, gut microbiome composition was more strongly associated than chronological age with most inflammatory and physiological measures examined.
- A microbial community pattern called the Bacteroides 2 enterotype was associated with higher inflammation and less favorable metabolic characteristics.
- Some inflammatory and metabolic measurements seen in young adults with Bacteroides 2 were not reached by other microbiome groups until decades later. This does not mean their bodies were literally decades older.
- In a prospective analysis of 2,259 participants, Bacteroides 2 was associated with a 21% higher relative hazard of subsequent hospital associated diagnoses.
- The study was observational. It does not show that changing the microbiome can slow aging or prevent disease.
Introduction
Gut microbiome composition may be linked to systemic inflammation and future disease risk, according to research examining microbial patterns in Danish adults.
People of the same chronological age can have very different levels of inflammation, metabolic health and disease risk. New research suggests that the gut microbiome may capture some of those differences.
A study published September 8, 2026, in Nature Communications compared gut microbial composition with inflammatory markers, physiological measurements and subsequent disease in Danish adults.
Among 1,199 participants with paired microbiome and cytokine data, microbiome composition explained more statistical variation than chronological age for 29 of 30 inflammatory cytokines and 16 of 19 biochemical and physiological measures.
One microbial community pattern, called the Bacteroides 2 enterotype, was associated with higher inflammation and a less favorable metabolic profile. In a larger prospective analysis, it was also associated with a 21% higher relative hazard of subsequent hospital associated diagnoses (Eriksen et al., 2026).
The findings strengthen evidence connecting gut microbial ecology with inflammation and health across adulthood. They do not establish that the microbiome determines biological age or causes disease.
What the Study Examined
Participants came from the Danish Study of Functional Disorders, or DanFunD, a population based cohort in the greater Copenhagen area.
The larger cohort enrolled 7,493 adults. Researchers had paired fecal microbiome and cytokine data from 1,199 participants ages 20 to 72 for the main microbiome and inflammation analyses.
They measured 30 plasma cytokines and 19 biochemical and physiological variables. Fecal microbiota were characterized using 16S ribosomal RNA gene sequencing.
Researchers identified four recurring microbial community patterns, or enterotypes: Bacteroides 1, Bacteroides 2, Prevotella and a high diversity group called Richness. Bacteroides 2 represented about 17% of the paired sample.
For the prospective disease analysis, Danish national health registers allowed researchers to follow 2,259 participants with fecal microbiome data and available smoking information. Follow up averaged approximately 8 years and extended for as long as 9 years (Eriksen et al., 2026).
The Microbiome Was More Strongly Associated With Many Health Measures Than Age
Microbiome composition accounted for more statistical variation than chronological age for 29 of 30 cytokines, or 97%, and 16 of 19 biochemical and physiological variables, or 84% (Eriksen et al., 2026).
Those percentages require careful interpretation.
They do not mean the microbiome explains 97% of a person’s inflammation. They mean microbiome composition explained more variation than chronological age for 97% of the individual cytokines researchers examined.
The physiological measures included markers related to body composition, blood lipids, glucose regulation and cardiovascular fitness.
Researchers also assessed whether major findings could be reproduced using available measurements from the independent European MetaCardis cohort. Several of the principal relationships were replicated, strengthening confidence that they were not unique to the Danish sample (Eriksen et al., 2026).
Bacteroides 2 Stood Out
Participants with the Bacteroides 2 enterotype showed the clearest unfavorable profile.
After adjustment for age, this group had higher levels of eight inflammatory markers, including C reactive protein, interleukin 6 and tumor necrosis factor alpha. Participants with Bacteroides 2 also had higher average BMI and triglycerides, lower HDL cholesterol and lower estimated VO2 max (Eriksen et al., 2026).
Researchers then compared how several measurements varied with age across the microbiome groups.
For some markers, levels already observed among 20 year old participants with Bacteroides 2 were not reached by participants with other enterotypes until decades later. For several inflammatory measures, the modeled difference reached approximately 37 years (Eriksen et al., 2026).
This does not mean people with Bacteroides 2 were biologically 37 years older.
Researchers compared modeled age related trajectories for particular inflammatory and physiological measurements. They did not calculate a validated biological age for each participant.
The differences also changed with age. Levels of several inflammatory cytokines converged among the enterotypes by approximately age 65 (Eriksen et al., 2026).
Bacteroides 2 Was Associated With Subsequent Disease
Researchers next examined hospital associated diagnoses recorded in Danish national health registers.
Compared with the other three enterotypes combined, Bacteroides 2 was associated with a 21% higher relative hazard of a subsequent hospital associated diagnosis, corresponding to an overall hazard ratio of 1.21 (Eriksen et al., 2026).
Significantly higher hazards were reported across 7 of the 13 disease chapters examined, including circulatory, digestive, respiratory, musculoskeletal and nervous system disorders, eye disorders and infections.
The high diversity Richness enterotype showed the opposite overall pattern, with a lower hazard of subsequent disease (Eriksen et al., 2026).
The 21% figure describes relative hazard. It does not mean that 21% of people with Bacteroides 2 became ill or that an individual’s absolute disease risk increased by 21 percentage points.
Could Inflammation Help Connect the Microbiome With Disease?
Researchers also investigated whether inflammation could statistically account for part of the association between Bacteroides 2 and later disease.
Their mediation analysis indicated that the combined cytokine profile accounted for about 4.1% of the overall association, with larger proportions for some disease categories (Eriksen et al., 2026).
That is consistent with inflammation being one possible pathway connecting microbial ecology with disease, but mediation analysis cannot establish the biological mechanism.
The researchers did not experimentally alter either the microbiome or inflammatory pathways. Other factors may influence both, and existing disease processes could themselves change the intestinal environment.
How It Compares With Earlier Research
Bacteroides 2 had attracted scientific attention before the new Danish study.
Vieira Silva and colleagues characterized Bacteroides 2 as a low microbial density configuration associated with systemic inflammation. Among participants who were not taking statins, its prevalence increased from 3.9% among lean or overweight participants to 17.7% among those with obesity. The researchers also found evidence that the inflammatory profile associated with Bacteroides 2 could not simply be explained by obesity (Vieira-Silva et al., 2020).
The new study extends that evidence by connecting Bacteroides 2 with age related inflammatory patterns and subsequent hospital associated diagnoses.
Other researchers have approached the relationship between the microbiome and aging from a different direction.
Wilmanski and colleagues analyzed gut microbiome data from more than 9,000 people across three independent cohorts. Beginning in mid to late adulthood, healthier individuals tended to develop increasingly distinctive gut microbiomes. Among older adults, greater microbiome uniqueness was associated with favorable health characteristics and better survival (Wilmanski et al., 2021).
The Wilmanski and Eriksen studies measured different microbiome characteristics, so they should not be considered direct replications. Together, however, they support a broader relationship between gut microbial ecology and health during aging.
Geography Complicates the Picture
There is an important reason not to interpret any one microbiome pattern as a universal definition of gut health.
Human gut microbial communities vary substantially among populations.
Ecklu Mensah and colleagues studied people of African origin living in Ghana, South Africa, Jamaica, Seychelles and the United States. Country of residence explained more variation in microbiome composition than obesity status, and relationships between microbiome characteristics and cardiometabolic traits differed among countries (Ecklu-Mensah et al., 2023).
That matters because the new study was based primarily on a Danish population.
Although the investigators reproduced several findings using data from the European MetaCardis cohort, results from European populations cannot automatically be assumed to apply identically to populations with different diets, environments, medications, lifestyles and early life exposures.
What the Results May Mean
The study suggests that gut microbial composition contains information about inflammation and physiology that chronological age alone does not capture.
That does not make Bacteroides 2 an infection or clinical diagnosis. Bacteroides bacteria are common members of the human intestinal microbiome. Bacteroides 2 instead describes a broader microbial community configuration.
The findings also do not validate consumer microbiome testing as a way to determine biological age or predict an individual’s future disease.
Most importantly, researchers did not test whether deliberately changing the microbiome improves health.
Diet, medications, antibiotics and other exposures can alter gut microbial communities. But the study did not test probiotics, prebiotics, dietary interventions, fecal microbiota treatments or other approaches intended to change a person’s microbiome (Eriksen et al., 2026).
Whether moving away from a Bacteroides 2 pattern would reduce inflammation or disease risk therefore remains unknown.
Limitations
The observational design is the study’s most important limitation. Researchers measured naturally occurring microbiome differences rather than experimentally changing them, so causation cannot be established.
Residual confounding is also possible. Diet, medications, smoking, physical activity and existing health conditions can influence both gut microbiota and health. The investigators adjusted for several potential confounders, but detailed dietary information was limited (Eriksen et al., 2026).
Reverse causation is another possibility. Existing metabolic, inflammatory or disease processes may alter the microbiome rather than simply result from it.
Generalizability also requires caution. The primary cohort was Danish, and other research has demonstrated substantial geographic variation in human microbiomes (Ecklu-Mensah et al., 2023).
Finally, enterotypes reduce an extremely complex microbial ecosystem to broad categories. They are useful research classifications, not established clinical diagnoses.
Final Thoughts
The study provides detailed human evidence connecting gut microbiome composition with systemic inflammation, physiology and subsequent disease.
Among Danish adults with paired microbiome and cytokine measurements, microbiome composition was more strongly associated than chronological age with most of the inflammatory and physiological measures examined.
Bacteroides 2 was particularly notable. It was associated with an inflammatory and metabolically unfavorable profile that appeared substantially earlier in adulthood for some measurements. In the prospective analysis of 2,259 participants, it was also associated with a 21% higher relative hazard of subsequent hospital associated diagnoses (Eriksen et al., 2026).
Earlier research independently connects Bacteroides 2 with systemic inflammation (Vieira-Silva et al., 2020), while other large human studies have linked broader microbiome patterns with healthier aging and survival (Wilmanski et al., 2021). Geographic research also cautions against assuming that one microbial configuration represents optimal health for everyone (Ecklu-Mensah et al., 2023).
The central unanswered question is whether these microbiome differences merely reflect health and aging or contribute to causing some of the changes associated with them.
Answering that question will require intervention studies showing that deliberately altering the microbiome improves meaningful health outcomes.
References
Ecklu-Mensah, G., et al. (2023). Gut microbiota and fecal short chain fatty acids differ with adiposity and country of origin: The METS Microbiome study. Nature Communications, 14. https://doi.org/10.1038/s41467-023-40874-x
Eriksen, C., Chatzigiannidou, I., Dehli, R. K., Johansen, P. L., Dantoft, T. M., Pedersen, O., Hansen, T., Linneberg, A., Jess, T., Allin, K. H., Jørgensen, T., Kristiansen, K., & Brix, S. (2026). Gut microbiota composition outperforms chronological age in predicting systemic inflammation and incident disease risk. Nature Communications. https://doi.org/10.1038/s41467-026-77499-9
Vieira-Silva, S., et al. (2020). Statin therapy is associated with lower prevalence of gut microbiota dysbiosis. Nature, 581, 310–315. https://doi.org/10.1038/s41586-020-2269-x
Wilmanski, T., et al. (2021). Gut microbiome pattern reflects healthy ageing and predicts survival in humans. Nature Metabolism, 3, 274–286. https://doi.org/10.1038/s42255-021-00348-0
