Methionine-200 provides a supplemental source of the sulphur-bearing amino acids Methionine, Lysine and Cysteine. L-Methionine is essential for human health, and in addition to being a sulfur containing amino acid, it also functions as a methyl donor, giving off a methyl group as needed for a variety of chemical and metabolic reactions in the body. In the liver methionine is converted into SAMe (S-adenosyl methionine). Strict vegetarians or persons on a low protein diet may need additional methionine in their diet. Additionally, advanced age is associated with a loss of methionine sulfoxide reductase activities in a number of tissues, thus with advancing age a supplemental source of Methionine may be required. Methionine and cysteine protein residues are particularly sensitive to oxidation by ROS, which is also impacted by age.