Researchers who linked an age-related failure in the ability to process the amino acid leucine to progressive muscle loss, or sarcopenia, continue to search for the root cause: "Because aging is associated with changes in oxidative status, we hypothesized that reactive oxygen species-induced oxidative damage may be involved in the impairment of the anabolic effect of leucine with age. The present study assessed the effect of antioxidant supplementation on leucine-regulated protein metabolism in muscles from adult and old rats. ... In old rats, the ability of leucine to stimulate muscle protein synthesis was significantly decreased compared with adults. This defect was reversed when old rats were supplemented with antioxidants [but it] was not related to increased oxidative damage ... These effects could be mediated through a reduction in the inflammatory state, which decreased with antioxidant supplementation. Antioxidant supplementation could benefit muscle protein metabolism during aging, but further studies are needed to determine the mechanism involved and to establish if it could be a useful nutritional tool to slow down sarcopenia with longer supplementation." Given a weight of evidence for the ineffectiveness of ingested antioxidants, a reduction in inflammation and the widespread damage it causes sounds more plausible.

Link: http://www.ncbi.nlm.nih.gov/pubmed/18932012