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The gut microbiota, composed of the community of bacteria, archaea, fungi, and viruses that live in the human intestine, influences human health, aging, and disease. Previous research has demonstrated that microbial diversity, a measure associated with good health, decreases with age; however, these studies utilized stool samples to characterize the microbiota, which may not be representative of the entire gut. Findings of a new study utilizing intestinal samples demonstrate that the microbiota of the small intestine changes markedly with the aging process.

Aging is associated with a wide range of physiological changes (such as increased inflammation, metabolic dysfunction) and a weakened immune system, and behavioral changes (such as increased medication use, reduced diet quality, and reduced physical activity). These changes reduce the number of species capable of surviving in the intestinal environment, reducing overall diversity. This less diverse microbiota is less able to crowd-out dangerous microbes such as coliform pathogens. While not all coliforms are dangerous, an increased abundance is associated with small intestinal bacterial overgrowth and inflammatory bowel disease. Centenarians, people who live beyond 100 years of age, exhibit higher microbiota diversity and higher capacity for producing beneficial microbial products such as short-chain fatty acids, demonstrating a relationship between microbiota quality and longevity.

The researchers collected microbiota samples from 251 patients undergoing an upper endoscopy, an imaging procedure where a camera is used to view the esophagus, stomach, and small intestine. Participants ranged in age from 18 to 80 years old. Participants completed questionnaires about their medical history and gave a blood sample. The researchers measured blood lipids, glucose, insulin and other hormones, and inflammatory cytokines.

The researchers found that the region of the gastrointestinal tract where diversity was most perturbed by age was the duodenum, the first portion of the small intestine that connects to the stomach. However, there were other variables that interfered with this statistical relationship. Duodenal microbial diversity decreased with chronological age but also with the number of medications used and the number of medical conditions reported. The authors interpreted this to mean that the microbiota becomes less diverse due to the aging process instead of simple chronological age. While some bacterial families remained stable over the lifespan, others such as the coliform genera Escherichia increased with chronological age and Klebsiella increased with the number of medications used.

The authors concluded that the microbiota of the small intestine becomes less diverse due to the aging process, allowing the bloom of disease-promoting bacteria. Lifestyle interventions that improve the aging process by reducing the number of medical conditions and medications used may improve microbiota quality.

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