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Western Human Nutrition Research Center, Agricultural Research Service, United States Department of Agriculture, Presidio of San Francisco, CA 94129
Since no reliable functional markers of human vitamin C status have been demonstrated, determination of vitamin C levels in blood plasma and/or leukocytes remains the current choice for individual and population assessments. Newer analytical techniques, especially high-performance liquid chromatography, allow determination of reduced (ascorbic acid), oxidized (dehydroascorbic acid), or total amounts of vitamin C in biological specimens or foods. Plasma levels of vitamin C forms are easily determined but may not reflect tissue content as well as leukocyte levels. The vitamin C content of leukocyte cell types varies severalfold and, unlike plasma, leukocytes may contain an appreciable fraction of dehydroascorbic acid. The effects of sex, age, cigarette smoking, drugs, and physiological factors on vitamin C levels are better known for plasma than leukocytes. To realize the potential of leukocytes as measures of vitamin C status, continued work is needed in standardizing the methodology and interpretive guidelines and simplifying the technique for blood processing. The search for specific functional markers of vitamin C deficiency should continue. Candidate markers may involve pathways of carnitine or collagen metabolism, immunocompetence, or antioxidant defense.
KEY WORDS: vitamin C vitamin C status vitamin C methods ascorbic acid nutritional assessment
1 Presented as part of a conference, "Nutrition Monitoring and Nutrition Status Assessment", at the first fall meeting of the American Institute of Nutrition, Charleston, South Carolina, December 810, 1989. The conference was supported in part by cooperative agreement HPU880004-02-1 with the DHHS Office of Disease Prevention and Health Promotion, the USDA Human Nutrition Information Service, the DHHS National Center for Health Statistics, and the International Life Sciences Institute-Nutrition Foundation.
2 The Planning Committee for the meeting consisted of Drs. Helen A. Guthrie, Roy J. Martin, Linda D. Meyers, James A. Olson, Catherine E. Woteki, and Richard G. Allison (ex officio). The symposium papers were edited by a committee consisting of Dr. James Allen Olson (coordinator), Dept. of Biochemistry & Biophysics, Iowa State University, Ames, IA; Dr. Cathy C. Campbell, Division of Nutritional Sciences, Cornell University, Ithaca, NY; Dr. Roy J. Martin, Dept. of Foods & Nutrition, University of Georgia, Athens, GA; and Dr. Catherine E. Woteki, Food & Nutrition Board, National Academy of Sciences, Washington, DC.
Manuscript received 10 December 1989. Revision accepted 11 July 1990.
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