Vitamin B-6 metabolism and status in young and middle-aged women Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/np193c36j

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  • To investigate the responses of healthy adult women to two levels of vitamin B-6, a seven week two-part experiment was conducted with five young adults and eight middle-aged subjects. During the four unsupplemented weeks, dietary vitamin B-6 was 2.3-2.4 mg/day. In the final three weeks, the same diet was supplemented with 8.0 mg pyridoxine to give an intake of 10.3-10.4 mg/day. Plasma pyridoxal 5'-phosphate (PLP), plasma and urinary vitamin B-6 (PB6, UB6), and urinary 4-pyridoxic acid (4PA) were monitored throughout the study as indicators of status. Tryptophan load tests (TLT) were administered twice at each vitamin B-6 intake. The older women had significantly lower PLP, PB6 and UB6 and slightly higher 4PA values on normal vitamin B-6 intakes. With supplementation, in both age groups, the circulating status indicators increased 3-4 fold and excreted indicators increased 5-6 fold. During the supplemented weeks, only the difference in UB6 remained significant between age groups. The TLT revealed no between-group differences in xanthurenic acid or kynurenic acid excretion. Erythrocyte pyridoxine kinase activity differences (p < 0.05) between the groups were documented, with the older women being 50% higher throughout. Supplementation did not alter kinase activity. Plasma and erythrocyte magnesium were likewise unchanged with supplementation and did not differ between groups. These results demonstrate an age related difference in vitamin B-6 status in women under controlled conditions of dietary intake with adequate vitamin B-6. They support results of studies done under less controlled conditions. The decrease in circulating levels and increase in excretory product may be a reflection of age-related metabolic changes suggesting increased catabolism. The disappearance of significant age differences in three of four status indicators with vitamin B-6 supplementation suggests there may be age differences in the requirement for this vitamin. Constant TLT results, however, suggest that 2.3 mg/day is adequate for both groups of women.
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