Vitamin B-6: a status report.
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.
Leklem
J E
JE
Department of Nutrition and Food Management, Oregon State University, Corvallis 97331-5103.
D004912:Erythrocytes / Q000201:enzymology; D006801:Humans; D008099:Liver / Q000378:metabolism; D008715:Methionine / Q000378:metabolism; D015596:Nutrition Assessment; D009752:Nutritional Status; D011730:Pyridoxal / Q000097:blood; D011732:Pyridoxal Phosphate / Q000097:blood; D011735:Pyridoxic Acid / Q000652:urine; D011736:Pyridoxine / Q000032:analysis* / Q000097:blood / Q000652:urine; D000637:Transaminases / Q000097:blood; D014364:Tryptophan / Q000378:metabolism
D011730:Pyridoxal; D011735:Pyridoxic Acid; D011732:Pyridoxal Phosphate; D014364:Tryptophan; D008715:Methionine; D000637:Transaminases; D011736:Pyridoxine