Age-Related Changes Occur in Small Intestine Microbiome

By Marilynn Larkin

October 18, 2021

NEW YORK (Reuters Health) - For the first time, researchers have uncovered links between age and changes in the small intestine microbiome, including decreased microbial diversity, increased coliforms, and bacteria that increase with chronological age alone.

"We believe that the small bowel is really a remarkable place," Dr. Ruchi Mathur of Cedars-Sinai in Los Angeles told Reuters Health by email. "It's so dynamic, and we feel that the microbiome of the small intestine plays a crucial role in human health and disease."

"In previous studies, we have shown that the microbial milieux of the small bowel are markedly different from the large bowel, and poorly represented by stool," she said. "We note that microbial diversity of the small intestine decreases with the aging process. Diversity may be a sign of a healthy microbiome, and this decrease with age is important to note."

"We also see an increase in bacteria that are less oxygen-dependent," she noted. "Whether this change is adaptive, or whether it is maladaptive is not clear."

"In addition, we see an increase in coliforms, (bacteria) that are present in the human GI tract," she said. "In modest amounts, they do no harm. The increase can be related to weeds in a garden. When the relative abundance of weeds increases, the rest of the garden can potentially suffer."

"Interestingly," she added, "we looked specifically at chronological age, and compared this to the number of medications associated with aging and with burden of underlying medical conditions, and we see a difference in the microbial profiles in each of these analyses."

The team's investigation, published in Cell Reports, consisted of analyses of the duodenal microbiome of 251 individuals recruited for the REIMAGINE study who underwent esophagogastroduodenoscopy without colon preparation.

Participants were categorized by chronological age: 18-35 (32 participants); 36-50 (41); 51-65 (96); and 66-80 (82). The analyses yielded the following findings:

- Decreased duodenal microbial diversity in older adults is associated with combinations of chronological age, number of concomitant diseases, and number of medications used, and also correlated with increasing coliform numbers.

- Relative abundance of phylum Proteobacteria and anaerobes increase in older individuals and is associated with alterations in other duodenal microbial taxa, as well as decreased microbial diversity.

- Bacteroides, Lactobacillus, and Escherichia increase with chronological age alone.

- Klebsiella increases with medication use.

- Clostridium increases with the number of concomitant diseases.

The authors conclude, "These findings indicate the small intestinal microbiome changes significantly with age and the aging process."

Dr. Mathur said, "At this moment, we cannot imply causality nor can we endorse manipulation of the small intestinal microbiome in order to promote healthy aging. However, by teasing apart the microbial changes associated specifically with chronological age, we may be able to target specific organisms for further investigation and therapeutic opportunities to enhance healthy aging and longevity."

Dr. Melinda Ring, executive director of the Osher Center for Integrative Medicine at Northwestern Medicine in Chicago, commented in an email to Reuters Health, "This report of small intestinal microbiome changes with aging builds upon the growing mass of data relating our gut microbiome to diverse markers of health and longevity."

"Since 90% of the digestion and absorption of food occurs in the small bowel, alterations in the microbiome may significantly impact health," she said. "While at this point, we don't have enough information to use these findings to recommend for or against probiotics, it is conceivable that down the road interventions to assess and optimize the whole gut microbiome will be a part of personalized medicine."

SOURCE: Cell Reports, online September 28, 2021.