Abstract: This invention embodies use of exogenous L-citrulline not only for support of capillary endothelial function, by L-citrulline bioconversion to plasma L-arginine to provide more cell substrate for enzymatic generation of nitric oxide, but also for providing more L-arginine in cellular microenvironments including that in acidified endosomes and lysosomes for potential chelation to free bivalent iron. Thus, it is contemplated that cellular oxidative damage from hydroxyl free radicals generated by Fenton-like reactions between bivalent iron and diffusible hydrogen peroxide will be ameliorated or prevented in age-related macular degeneration and in several nervous system age-related degenerative diseases by oral L-citrulline supplementation.