Vitamin B-6 status of women with a constant intake of vitamin B-6 changes with three levels of dietary protein.
To determine the effect of varying levels of dietary protein with a constant intake of vitamin B-6 (B-6) on B-6 status, nine women were fed diets providing daily intakes of 1.25 mg B-6 and 0.5, 1.0 and 2.0 g protein/kg body weight. After an 8-d adjustment period, the women consumed each level of dietary protein for 14 d in a Latin-square design. Several direct and indirect B-6 status indicators were measured in blood and urine. Significant differences among protein levels were found for urinary 4-pyridoxic acid (4-PA) excretion (P < 0.01), plasma pyridoxal 5'-phosphate (PLP) concentration (P < 0.05), and urinary excretion of volatile amines (VA, kynurenine plus acetylkynurenine) after a 2-g L-tryptophan load (P < 0.05). Nitrogen intake was significantly negatively correlated with urinary 4-PA excretion (r = -0.619, P < 0.001) and plasma PLP concentration (r = -0.549, P < 0.01), and positively correlated with erythrocyte alanine aminotransferase percentage stimulation (r = 0.418, P < 0.05) and urinary post-tryptophan load excretion of xanthurenic acid (r = 0.535, P < 0.05), kynurenic acid (r = 0.563, P < 0.05) and VA (r = 0.626, P < 0.01). Compared with men consuming diets with similar B-6 to protein ratios In a previous study, the women excreted a greater percentage of the B-6 intake as 4-PA, had lower plasma PLP concentrations and excreted greater amounts of postload urinary tryptophan metabolites at all three protein levels. If the Recommended Dietary Allowance (RDA) of vitamin B-6 is to be based on the dietary B-6 to protein ratio, gender differences in response to varying protein intakes should be considered. For the levels of protein intake used in this study and a B-6 intake of 1.25 mg/d, a B-6 to protein ratio of greater than 0.020 mg/g is required for adequate vitamin B-6 status in women.
Hansen
C M
CM
Department of Nutrition and Food Management, Oregon State University, Corvallis 97331, USA.
Leklem
J E
JE
Miller
L T
LT
D000328:Adult; D000469:Alkaline Phosphatase / Q000097:blood; D003404:Creatinine / Q000652:urine; D004044:Dietary Proteins / Q000008:administration & dosage* / Q000378:metabolism; D005260:Female; D006801:Humans; D009751:Nutritional Requirements; D009752:Nutritional Status; D011735:Pyridoxic Acid / Q000652:urine; D011736:Pyridoxine / Q000008:administration & dosage / Q000378:metabolism*; D012727:Sex Characteristics; D014364:Tryptophan / Q000008:administration & dosage
D004044:Dietary Proteins; D011735:Pyridoxic Acid; D014364:Tryptophan; D003404:Creatinine; D000469:Alkaline Phosphatase; D011736:Pyridoxine