Taurine — Sulfonic amino acid — conditionally essential / abundant in muscle, heart, brain, retina; declining with age

Taurine is one of the most abundant amino acids in the human body, found at high concentrations in skeletal muscle (50 mM), brain, retina, and cardiac tissue. It is conditionally essential — synthesized from methionine/cysteine but biosynthetic capacity declines with age. Key 2023 finding (Singh et al., Science 2023, PMID: 37289910): plasma taurine levels decline 80% from youth to old age across species (mice, monkeys, humans). In mice, taurine supplementation increased median lifespan 10–12% when started at middle age. Mechanisms: (1) Taurine is the most abundant intracellular osmolyte — maintains cell volume, stabilizes membranes, and prevents protein aggregation; (2) Conjugates with bile acids (taurocholate) to facilitate fat digestion and gut microbiome balance; (3) Modulates GABA-A and glycine receptor function — calming/neuroprotective; (4) Reduces mitochondrial ROS via complex I protection; (5) Attenuates telomere shortening; (6) Reduces DNA damage markers (8-OHdG); (7) Suppresses NF-κB inflammatory signaling; (8) Improves insulin sensitivity and reduces visceral adiposity in rodent studies; (9) Restores stem cell pools in muscle and brain in aging mice.