Creatine

Creatine is a guanidino compound synthesized endogenously in liver and kidney from arginine, glycine, and methionine, and obtained exogenously from red meat, fish, and supplements. As phosphocreatine, it rapidly regenerates ATP from ADP via the creatine kinase reaction during high-intensity efforts, buffering energy supply in muscle and brain. Creatine monohydrate supplementation (3–5 g/day after an optional loading phase) is one of the most extensively validated ergogenic aids, consistently increasing lean mass and strength in resistance-trained adults across meta-analyses. Emerging evidence in older adults indicates additional benefits on muscle preservation and fall prevention, with some RCTs and meta-analyses also suggesting modest cognitive effects — particularly relevant because older adults have lower dietary creatine intake and endogenous synthesis declines. Safety at habitual supplementation doses is well established in healthy adults, though those with pre-existing kidney disease should consult a physician.