Effect of age on changes in plasma, erythrocyte, and urinary B-6 vitamers after an oral vitamin B-6 load.

We investigated the effect of age on indices of vitamin B-6 metabolism in 36 fasting males aged 25-35, 45-55, and 65-75 y who ingested 17.15 mumol vitamin B-6. There were no significant differences among groups in dietary vitamin B-6 intake, base-line erythrocyte pyridoxal 5'-phosphate (PLP), and total vitamin B-6 concentrations, and 24-h and base-line urinary excretion of total vitamin B-6 and 4-pyridoxic acid (4-PA). Base-line plasma PLP and total vitamin B-6 were higher (p less than 0.05) in the youngest group. Increased serum alkaline phosphatase (AP) and decreased dietary vitamin B-6 intake were correlated with decreased base-line plasma PLP and total vitamin B-6. Changes in plasma and erythrocyte PLP concentrations and excretion of 4-PA and total vitamin B-6 postload were not different among groups. Indices of vitamin B-6 absorption, phosphorylation, and excretion were not affected by age.