“Three key findings emerged: First, lower serum concentrations of primary bile acids synthesized in the liver from cholesterol were significantly associated with worse cognitive function, decreased hippocampal volume, and decreased brain glucose metabolism.
Second, higher serum concentrations of secondary bile acids produced in the gut by bacteria were significantly associated with higher CSF phosphorylated tau and CSF total tau levels, as well as larger brain structural atrophy and decreased brain glucose metabolism.
Third, higher serum concentrations of ratios of bacterially produced secondary bile acids to primary bile acids were significantly associated with lower CSF Aβ1-42 values, larger brain structural atrophy, and decreased brain glucose metabolism."