L-Carnosine is a dipeptide composed of the amino acids beta-alanine and L-histidine. It occurs naturally in muscle, brain and other tissues in high concentrations. In in vitro studies, L-carnosine reduced glycation, a process in which DNA and protein are damaged by glucose. The end products of glycation are highly reactive molecules called advanced glycation end products (A.G.E.'s), which can further damage proteins, lipids and nucleic acids. The accumulation of A.G.E.'s is associated with aging. L-Carnosine has also been found to rejuvenate cells that were approaching senescence, according to human cell culture studies. Senescence occurs when older cells, unable to rejuvenate through cell division, become deformed and unable to function at previous levels.