Handbook of Vitamin C Research

Vitamin C: Dietary Requirements, Dietary Sources, and Adverse Effects 141ConclusionVitamin C intake can prevent and treat a large panel of diseases. The current RDA ofvitamin C for nonsmoking women and men is 75 mg and 90 mg, respectively. The totality ofthe evidence reported herein suggests that these doses of vitamin C are optimal in thispopulation both as an essential nutrient as well as an effective antioxidant. However, theRDA for vitamin C does not cover the need for vitamin C in daily bodily functions. Evidencefrom a number of studies shows that consumption of vitamin C at doses higher than the RDAenhances the immune system and decreases the risk of DNA damage. Vitamin C greater than400 mg/day can protect against oxidative stress, certain cancers, and degenerative andchronic diseases. While higher dosages are generally well tolerated, the tolerable upper levelof vitamin C is 2 g.Modern farming methods lead to a lowering in food quality, inducing a considerable lossof micronutrients. The result is that people do not have sufficient intake of vitamin C throughfood consumption. Consequently, even if vitamin C requirements vary greatly amongindividuals, it is suggested that vitamin C supplementation is not only completely safe, butalso necessary to achieve optimal health. Therefore, in agreement with the current literature,we advise healthy people to consume five servings of fruits and vegetables daily, added to 1 gof vitamin C supplementation divided in two or three doses during the day, in order to ensurean optimal allowance in vitamin C.In response to the aggressive promotion and advertising by health food advocates of theneed for nutritional and antioxidant supplements, patients may seek information fromhealthcare providers about this issue. Clinicians should be cognizant about such issues andshould be prepared to provide their patients with evidence-based recommendations. In theircomprehensive approach to patient care, clinicians should base the need for recommendingdosages in excess of the RDA on sound data supported by a nutritional analysis and thepatients‘ plasma vitamin C concentration (normal: >0.2 mg/dl) levels.References[1] Leger, D. (2008). Scurvy: reemergence of nutritional deficiencies. Can Fam Physician,54, 1403-6[2] Levine, M., S.C. Rumsey, R. Daruwala, J.B. Park&Y. Wang (1999). Criteria andrecommendations for vitamin C intake. JAMA, 281, 1415-23[3] Linster, C.L.&E. Van Schaftingen (2007). Vitamin C. Biosynthesis, recycling anddegradation in mammals. Febs J, 274, 1-22[4] Nishikimi, M.&K. Yagi (1991). Molecular basis for the deficiency in humans ofgulonolactone oxidase, a key enzyme for ascorbic acid biosynthesis. Am J Clin Nutr,54, 1203S-08S[5] Nishikimi, M., R. Fukuyama, S. Minoshima, N. Shimizu&K. Yagi (1994). Cloning andchromosomal mapping of the human nonfunctional gene for L-gulono-gamma-lactoneoxidase, the enzyme for L-ascorbic acid biosynthesis missing in man. J Biol Chem,269, 13685-8