GPT and sarcopenia: In older adults, lower serum ALT levels are associated with mortality60,61 and are thought to be a biomarker for increased frailty, sarcopenia, and/or reduced levels of pyridoxine (vitamin B6).62 Pyridoxine phosphate is a coenzyme for the synthesis of amino acids, neurotransmitters (eg, serotonin and norepinephrine), and sphingolipids.