Antioxidant 0.5% per year with an increase to 4.5% per year at UA supersaturation levels (535+ μmol/L). Many of these aforementioned studies determined UA's antioxidant actions within normal physiological levels, and some found antioxidant activity at levels as high as 285 μmol/L. Ascorbic acid or "vitamin C" is a monosaccharide oxidation-reduction (redox) catalyst found in both animals and plants. As one of the enzymes needed to make ascorbic acid has been lost by mutation during primate evolution, humans must obtain it from the diet; it is therefore a vitamin. Most other animals are able to produce this compound in their bodies
L-gulonolactone oxidase deficiency living in a malarial infested environment". He based his observation on evidence which indicates that G6PD deficient individuals display enhanced sensitivity to ascorbic acid induced hemolysis. Studies of human diseases have benefited from the availability of small laboratory animal models. However, the tissues of animal models with a GULO gene generally have high levels of ascorbic acid and so are often only slightly influenced by exogenous vitamin C. Guinea pigs, for instance, are a popular human model but lost the ability to synthesize L-gulono-gamma-lactone oxidase 20 million years ago. This is a major handicap for studies involving the endogenous