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Department of Nutrition and Food Management, Oregon State University, Corvallis, OR 97331-5103
Over the past 50 yr there has been an increased awareness of the importance of vitamin B-6 in human nutrition. The knowledge base for evaluation of vitamin B-6 status has also increased. Indices for vitamin B-6 status can be separated into direct and indirect measures. Among the direct measures, plasma pyridoxal 5'-phosphate (PLP) is considered the most relevant. However, measurement of plasma pyridoxal or total vitamin B-6 and urinary 4-pyridoxic acid are also recommended. Indirect measures of vitamin B-6 include the assessment of urinary excretion of xanthurenic acid following a tryptophan load. This is a valid functional index for otherwise healthy persons. Evaluation of erythrocyte transaminase activity and stimulation with PLP provide an estimate of vitamin B-6 intake over an extended period of time. In addition to biochemical measures, determination of vitamin B-6 and protein intake are necessary. Present evidence suggests plasma PLP, urinary 4-pyridoxic acid, at least one indirect measure, and the intake of vitamin B-6 and protein are needed to properly assess vitamin B-6 status. The levels of plasma pyridoxal and erythrocyte PLP are newer measures of status and, with further refinement of methodology, may provide additional insight into vitamin B-6 status.
KEY WORDS: vitamin B-6 pyridoxal 5'-phosphate pyridoxal 4-pyridoxic acid transaminases
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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