A new study published in Nature looked at gut microbiome patterns in three groups of people in Japan: 150 centenarians with an average age of 107 years old, 112 people between 85-89 years old, and 47 people who were 21-55 years of age. "A majority of the centenarians did not report any major chronic diseases, which is remarkable considering we expect aging to be associated with increases in chronic health conditions," says Arpana Gupta, PhD, an associate professor in the UCLA Vatche and Tamar Manoukian Division of Digestive Diseases at the David Geffen School of Medicine.
While researchers can't make a direct correlation between the microbiome composition of the centenarians, and the surprising absence of chronic conditions (like obesity, diabetes, hypertension, and cancer), they did find that this oldest living cohort had specific bacteria in their guts that produce secondary bile acids known to protect against certain types of bacterial infection, including those from drug-resistant germs. "They also boost the immune system in ways we don't quite understand," says Niket Sonpal, MD, an internist and gastroenterologist in New York City and faculty member at Touro College of Medicine.
When researchers took the secondary bile acids and tested them against bacteria in the lab, they found they were effective in defeating specific types of bacteria called Clostridioides difficile and Enterococcus faecium that causes inflammation in the gut, resulting in severe diarrhea. The bile killed other harmful pathogens in the gut, too.
What can we glean from this? Unfortunately, these new findings cannot conclude why these centenarians contain specific secondary bile acid-producing bacteria. "The microbiome develops over your lifetime, and it changes based upon what you eat, how you act, genetics, etc., and so there's something about this cohort of people...in that region of Japan [that's enabled this specific microbiome makeup]," says Dr. Sonpal.
In other words, it's not quite possible to determine the factors responsible for this microbiome advantage, so we can't artificially replicate it for the rest of the population. "[The specific bacterium] is just one factor in a multitude, so just finding out what bacterium it is and then giving it to other people might not work," Dr. Sonpal says.
And Dr. Gupta says these findings need to be interpreted with caution regarding long-term effects and the influence of diet, lifestyle, or genetics. She notes that to make causal inferences—e.g., that these secondary bile acids actually facilitate longevity—we need longitudinal studies that include a more geographically, ethnically diverse sample of individuals. "More studies are needed in order to determine what is known as a 'systems biology' integrated approach that can account for not only the influence of how the socio-cultural environment we live in impacts our biology but also how the gut communicates with other body systems such as the brain," she says.
Still, both experts say the findings are encouraging. Dr. Sonpal notes that if researchers can gain clarity around these variables, they could hypothetically use that knowledge to help others achieve similarly protective microbiome compositions and potentially live longer, healthier lives as a result.
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