The vitamin B-6 requirement of young women consuming a constant high-protein diet (1.55 g/kg body wt) and the effect of various ratios of vitamin B-6 to protein on this requirement were studied. Eight women were fed a lactoovovegetarian basal diet containing 0.45 mg vitamin B-6 (2.66 micromol as pyridoxine) and 30 micromol carnitine for 92 d. The protocol consisted of successive baseline adjustment (9 d), depletion (27 d), and repletion (two 21-d and then one 14-d) periods. Vitamin B-6 intakes were 1.60, 0.45, 1.26, 1.66, and 2.06 mg, resulting in ratios of vitamin B-6 (in mg) to protein (in g) for the five periods of 0.016, 0.005, 0.013, 0.017, and 0.021, respectively. Direct and indirect as well as short- and long-term vitamin B-6 status measures were assessed weekly. Regression analysis revealed that the amount of dietary vitamin B-6 required to normalize urinary 4-pyridoxic acid, plasma pyridoxal-P, erythrocyte pyridoxal-P and pyridoxal, and erythrocyte alanine and aspartate aminotransferase activity coefficients to predepletion baseline values was 1.94 mg vitamin B-6/d (0.019 mg vitamin B-6/g protein). This study suggests that the current vitamin B-6 recommended dietary allowance of 1.6 mg/d based on 0.016 mg/g protein is not an adequate intake and may require reevaluation.
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