Abstract: Described herein are methods for identifying or diagnosing Alzheimer's disease or poor cognition in a subject or population of subjects by analyzing biomarkers. In one aspect, the biomarkers comprise liver function enzymes or metabolites including alanine aminotransferase (ALT), aspartate aminotransferase (AST), ratio of ALT to AST, alkaline phosphatase, albumin, bilirubin, cholesterol and cholesterol metabolites, amino acids, phospholipids, bile acids, or other metabolites. In another aspect, the biomarkers comprise alanine aminotransferase (ALT), aspartate aminotransferase (AST), or the ratio of ALT to AST levels. In another aspect, the marker comprises the genotype of the ALT or AST enzymes.