Differences in vitamin B₆ status indicator responses between young and middle-aged women fed constant diets with two levels of vitamin B₆

The responses of adult women to two levels of vitamin B₆, was conducted with five young and eight middle-aged subjects. A constant diet (2.3–2.4 mg vitamin B₆ per day) was fed for four weeks followed by three weeks of the same diet supplemented with 8.0 mg pyridoxine. Plasma pyridoxal 5′-phosphate (PLP), plasma and urinary vitamin B₆, and urinary 4-pyridoxic acid (4-PA) were determined. The older women had significantly lower plasma PLP, plasma and urinary vitamin B₆ and slightly higher urinary 4-PA values on normal vitamin B₆ intakes. With supplementation, only the difference in urinary total vitamin B₆ remained significant. Tryptophan load tests revealed no significant between-group differences in xanthurenic acid or kynurenic acid excretion. These results demonstrate an age-related difference in vitamin status indicators in women under controlled dietary intake of vitamin B₆.