VITAMIN-B-6 STATUS OF WOMEN WITH A CONSTANT INTAKE OF VITAMIN-B-6 CHANGES WITH 3 LEVELS OF DIETARY-PROTEIN

To determine the effect of varying levels of dietary protein with a co nstant 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 pr otein/kg body weight. After an 8-d adjustment period, the women consum ed each level of dietary protein for 14 d in a Latin-square design. Se veral direct and indirect B-6 status indicators were measured in blood and urine. Significant differences among protein levels were found fo r urinary 4-pyridoxic acid (4-PA) excretion (P < 0.01), plasma pyridox al 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 negati vely correlated with urinary 4-PA excretion (r = -0.619, P < 0.001) an d plasma PLP concentration (r = -0.549, P < 0.01), and positively corr elated with erythrocyte alanine aminotransferase percentage stimulatio n (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 exc reted a greater percentage of the B-6 intake as 4-PA, had lower plasma PLP concentrations and excreted greater amounts of postload urinary t ryptophan 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 i n 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.