Handbook of Vitamin C Research

128Chin-San Liugenetic damage is unknown, although it has been suggested that it may have been due toradiation exposure, or possibly that the gene may have been mutated by a retrovirus [4, 6].Natural Sources of Vitamin CIn the mid-18th century, James Lind first demonstrated that the juice of fresh citrus curesscurvy. The active agent, the enolic form of 3-keto-L-gulofurnlactone, or ascorbic acid, wasisolated in the late 1920s [1]. By the mid-1930s, methods had been devised to synthesizeascorbic acid, making it widely available at low cost. Because humans are unable tosynthesize ascorbic acid, we obtain our daily requirements from natural sources, such ascitrus fruits (oranges, lemons, limes, grapefruits) and vegetables (potatoes, broccoli, spinach,Brussels sprouts, red peppers). Ascorbic acid can be easily destroyed by heat; therefore, manyfoods can lose their ascorbic acid content because of cooking, storage, or oxidation. Ascorbicacid is absorbed from the intestinal tract and has a biological half-life of approximately 30minutes. There is no storage site in the body; however, some tissues carry higherconcentrations (white blood cells, adrenal glands, pituitary gland) [7].Conventional farming methods, which employ toxic chemical products in order to carryout intensive production, present a great health hazard and severely decrease food quality [8,9]. Analysis of fruits and vegetables has shown a significant loss of minerals and traceelements in modern diets compared to that of a few decades ago [10, 11]. Moreover, aconsiderable loss of nutrients in the modern diet has been observed during food processing,long transporting, and incorrect food storage [12, 13]. Vitamin C in foods is irreversiblyoxidized by exposure to light, oxygen, and/or heat, and reports suggest that fresh produce orjuice may lose 50%–100% of its vitamin C content due to handling and processing [14-16].Hence, the increased processing of the food supply may be impacting the level of dietaryvitamin C available to consumers [17].Functions of Vitamin CA number of metabolic reactions require vitamin C as a cofactor, such as the synthesis ofepinephrine from tyrosine. Furthermore, vitamin C involvement is suspected in the process ofadrenal steroidogenesis. Other putative biochemical roles of ascorbic acid are in thyroxinesynthesis, amino acid metabolism, and aiding in the absorption of iron [18]. Vitamin C canquench aqueous reactive oxygen species [19], plays an important role in antioxidant defensesystem and immunocompetence [20], and in strengthening resistance to infection [18, 21]. Inaddition, vitamin C protects against deoxyribonucleic acid (DNA) mutations and, therefore,might be of clinical value in the treatment of certain types of cancer and other diseases [22-26].Vitamin C is required for the synthesis of collagen, an important structural component ofblood vessels, tendons, ligaments, and bone. Ascorbic acid also plays an important role in thesynthesis of norepinephrine, a neurotransmitter critical to brain function. In addition, vitaminC is required for the synthesis of carnitine, a small molecule that is essential for the transport