Handbook of Vitamin C Research

Vitamin C: Daily Requirements, Dietary Sources and Adverse Effects 253flavonol) is the most potent inhibitor. Quercetin significantly decreased ascorbate absorptionin normal rats given ascorbate plus quercetin compared with rats given ascorbate alone.Vitamin C plays an important role in embryogenesis and fetal growth as well as in theprogression of pregnancy and delivery. A recent study has shown that flavonoids (genisteinand quercetin) inhibit [ 14 C] ascorbic acid uptake in a dose-dependent and non-competitivemanner in the human trophoblast cell line HTR-8/SVneo (Biondi et al., 2007).Future StudyBy definition, an antioxidant is a substance that, in small quantities, reacts with radicalsto prevent the oxidation of other substances, and the resulting radical produced is relativelystable and does not promote oxidation (Atkins and Beran, 1992; Croft, 1998). However,based on Le Chatlier‘s principle, it is possible for an antioxidant compound to haveprooxidant activity at sufficiently high concentrations. It has been demonstrated in thepresented research that high concentrations of ascorbic acid may have prooxidant activity invivo. Continued study of the prooxidant activities and detrimental effects of megadosingascorbic acid should continue. As of now, there has been a very broad focus on theprooxidant effects of ascorbic acid and the relation to DNA damage, and it seems apparentthat high doses of ascorbic acid have adverse implications. Future studies should narrow theirfocus on the mechanisms of the reactions involved in the damage and determine the ranges ofascorbic acid concentrations which are the safest and also most dangerous.The world‘s human population is continuing to extend its average survival age, and withage, comes diminishing bodily functions. One of the functions that degrades with age is theability to absorb vitamin B 12 . The early studies that determined that ascorbic acid altered thechemical structure of vitamin B 12 should be revisited to determine a satisfactory method forprotecting this vitamin for biological usage.ConclusionVitamin C is uniquely important to the health and wellbeing of humans. It plays a crucialrole as a component of enzymes involved in the synthesis of collagen and carnitine, and it iswater-soluble antioxidant, which makes it indispensable for the development, normal growth,and functionality in human.Epidemiological studies show that dietary intake of fruits and vegetables high in vitaminC have been associated with a reduced risk of various types of cancer, particularly cancers ofthe mouth, esophagus, stomach, colon, and lung. However, it is not clear that the benefitcomes specifically from the vitamin C in the fruits and vegetables because higher intakes ofvitamin C by supplementation have not been found to be associated with this protectiveeffect. We postulate that synergistic and additive actions of vitamin C and other bioactivephytochemicals present in fruits and vegetables play a crucial role in prevention of sometypes of cancers. Therefore, the most prudent recommendation for supplying vitamin C is toconsume sufficiently high quantities of fruits and vegetables daily.