- Four studies were conducted to evaluate the effect of varying levels of vitamin
B-6 (B6), protein and pyridoxine glucoside (PNG) on B6 status and requirements of
women. In the first two studies, women were fed a constant protein diet and vitamin
B-6 intakes of 0.84 to 2.39 mg/d during 10- to 15-day experimental periods.
Significant differences among intake levels were found in urinary 4-pyridoxic acid
(4PA) and total vitamin B-6 (UB6), plasma pyridoxal 5'-phosphate (PLP) and total
vitamin B-6 (TB6), and urinary xanthurenic acid (XA) following a tryptophan load.
Significant correlations were found between B6 intake and 4PA, UB6, plasma PLP,
TB6, erythrocyte alanine aminotransferase (EALT) percent stimulation, and postload
urinary XA and volatile amines (VA, kynurenine plus acetylkynurenine). More than
1.33 mg B6/d (> 0.016 mg B6/g dietary protein) was required for adequate B6
status. In a third study, nine women were fed diets providing 1.25 mg B6/d and three
levels of protein (0.5, 1.0 and 2.0 g/kg body weight), for 14 days each. Significant
differences in urinary 4PA, plasma PLP, and postload urinary VA were found among protein levels. Nitrogen intake was significantly negatively correlated with urinary
4PA and plasma PLP, and positively correlated with EALT percent stimulation and
postload urinary kynuremc acid (KA), XA and VA. Compared to men in a previous
study, women excreted a greater percentage of B6 intake as 4PA, had lower plasma
PLP and greater amounts of postload urinary tryptophan metabolites. At least 0.020
mg B6/g protein was required for adequate status. In a fourth study, nine women
were fed diets with a high (27%) or low (9%) percentage of the B6 intake as
pyridoxine glucoside, a form known to have reduced bioavailability, for 18 days each.
Urinary 4PA and UB6, plasma TB6 and red blood cell PLP were significantly lower,
and fecal B6 was significantly higher during the high PNG diet. The decrease in B6
status indicators on the high PNG diet suggested a loss of 15 to 18% of the total B6
intake. Taking into account bioavailability and gender differences in the effect of
dietary protein, and including a safety margin, the RDA for B6 for women should be
at least 0.020 mg/g dietary protein.