Bile acids and gut bacteria age together

Bile acids are byproducts of cholesterol metabolism in the liver. They help absorb fats and fat-soluble vitamins, but they also act as signaling molecules that influence which bacteria survive in the gut. The study, published in Frontiers in Aging, compared bile acid profiles and gut microbiome composition between one hundred young and one hundred older participants.

In older participants, levels of primary bile acids, those produced directly by the liver, such as cholic acid and chenodeoxycholic acid, were lower. Secondary bile acids, which gut bacteria convert from primary bile acids, increased. At the same time, inflammatory markers including IL-6 and TNF-α were elevated. Bacteria that produce secondary bile acids were also more prevalent in older participants. This suggests a bidirectional relationship: the liver alters bile acids, gut bacteria respond, and those bacteria in turn influence bile acid composition.

A leaky gut wall as connecting link

A second factor is the intestinal barrier. With age, this barrier becomes more permeable (intestinal permeability). Bacterial waste products can then leak into the body. The researchers found elevated levels of LPS (lipopolysaccharide), a component of bacterial cell walls that can activate the immune system. Higher LPS levels were associated with specific bile acid changes in older participants. These findings are correlational; the study cannot establish a causal relationship.

Bile acid metabolism as a potential target

From a longevity perspective, this is noteworthy. If bile acids are partly modifiable through lifestyle or medication, this could influence gut microbiome composition. Animal studies have already shown that restoring a youthful microbiome improves health. Whether modulating bile acid metabolism produces comparable effects in humans remains an open question. The authors regard it as a promising target, not an established therapy.

Read the original article