Assessment of vitamin B-6 status in young women consuming a controlled diet containing four levels of vitamin B-6 provides an Estimated Average Requirement and Recommended Dietary Allowance

The Recommended Dietary Allowance (RDA) of vitamin B-6 for young women was recently reduced from 1.6 to 1.3 mg/d based on an adequate plasma pyridoxal phosphate (PLP) concentration of 20 nmol/L, To assess vitamin B-6 requirem ents and suggest recommendations for intake, seven healthy young women cons umed a controlled diet providing 1.2 g protein/kg body weight for a 7-d adj ustment period (1.0 mg vitamin B-6/d) and three successive 14-d experimenta l periods (1.5, 2.1 and 2.7 mg/d, respectively). Direct and indirect vitami n B-6 status indicators were measured in plasma, erythrocytes and urine. In dicators most strongly correlated with vitamin B-6 intake [i.e., plasma and erythrocyte PLP, urinary 4-pyridoxic acid (4-PA) and total vitamin B-6] we re regressed on vitamin B-6 intake and the dietary vitamin B-6 to protein r atio. Inverse prediction using adequate and baseline values estimated vitam in B-6 requirement. Adequate values were determined for plasma PLP and urin ary 4-PA from baseline values of 60 previous subjects, using the statistica l method suggested by Sauberlich. The current study suggests a vitamin B-6 Estimated Average Requirement (EAR) for young women of 1.1 mg/d or 0.016 mg /g protein, and a RDA of 1.5 mg/d or 0.020 mg/g protein. When results from this study are combined with data from four other recent studies, the combi ned data predict an EAR of 1.2 mg/d or 0.015 mg/g protein, and a RDA of 1.7 mg/d or 0.018 mg/g protein. This study suggests that the current vitamin B -6 RDA may not be adequate.