Handbook of Vitamin C Research

238Jun Yang, Jiaren Liu and John Parrywith increasing the susceptibility to Vitamin B 12 deficiency, and also has shown to becontraindicative in cancer chemotherapy. High doses of ascorbic acid may haveprooxidant effects and have also been implicated in the development of kidney stones. Invitro and animal studies have shown that fruit and vegetable components, such asflavonoids and other matrix compounds, might reduce ascorbic acid intestinal uptake.The role of ascorbic acid in human biology and health is still controversial. The healthbenefits of ascorbic acid have been the subject of much debate. More mechanisms ofaction and human in vivo studies are needed to understand and elucidate the molecularmechanisms of ascorbic acid in health functions. The purpose of this chapter is to reviewthe health benefits and adverse effects of ascorbic acid based on a review of theliterature.IntroductionVitamin C, known as ascorbic acid and ascorbate, is an essential vitamin for humans. It isfound in plants, animals, and single-cell organisms. Most mammals synthesize ascorbate fromglucose; however, due to a genetic defect, humans, guinea pigs, and some other primates arenot able to make the enzyme, L-gulonolactone oxidase, required for its synthesis (Shils1994). A deficiency in vitamin C in humans can lead to scurvy (Guthrie 1989), and maycause small cell-type anemia, atherosclerotic plaques, hemorrhages, poor wound healing,frequent infections, bone fragility and joint pain, rough skin and blotchy bruises, bleedinggums and loosened teeth, muscle degeneration, pain, hysteria, and depression (Whitney et al.,2002). Good sources of vitamin C are fruits and vegetables. An excessive intake of vitamin Csuch as gram doses and overdoses may lead to abdominal bloating, diarrhea, hyperoxalemiain dialysis patients, over absorption of iron, and hemolysis in patients with glucose-6-phosphate dehydrogenase deficiency (Jacob and Sotoudeh, 2002).Fruits and vegetables that are rich in vitamin C include citrus, green leafy vegetables,cantaloupe, tomatoes, mangoes, and papayas. Despite its abundance in fruits and vegetables,vitamin C is easily destroyed by light, heat, oxygen, and transition metals during storage andprocessing (Johnston 2001). So it must be stored in a dark, cold, and non-metallic container.It is easily oxidized and hence is used as a reductant and as a preservative. While prolongedstorage of unprocessed fruits and vegetables leads to the loss of vitamin C, food processingsuch as freezing and canning preserves vitamin C well.Vitamin C is crucial to the maintenance of bones, teeth, gums, ligaments, and bloodvessels. Due to its antioxidant activity, vitamin C has been used to help patients withischemic heart disease. Data suggest that vitamin C may have a benefit on blood flow in theheart but more research is needed to confirm these findings. Many health promotional usesfor vitamin C have been proposed, and some have been found to be beneficial in scientificstudies. However, some research in asthma, heart disease, cancer, and diabetes remainsinconclusive.