Response of vitamin B-6 content of muscle to changes in vitamin B-6 intake in men

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Abstract
Previous reports indicated that in growing rats the vitamin B-6 pool in muscle was relatively stable during deficiency but increased in response to increased vitamin B-6 intake. To determine whether human muscle would show a similar response 10 college-aged males received a low vitamin B-6 diet (1.76 µmol/d) for 6 wk followed by 6 wk on a self-selected diet supplemented with 0.98 mmol pyridoxine HCl/d. During depletion, excretion of pyridoxic acid rapidly adjusted to approximate the intake. Plasma pyridoxal phosphate concentrations at the end of the baseline, depletion, and supplementation periods were 81 ± 51,9 ± 3, and 455 ± 129 nmol/L, respectively, whereas muscle concentrations were 21 ± 9, 20 ± 4, and 25 ± 7 nmol/ g, respectively and total vitamin B-6 in muscle was 28 ± 10, 27 ± 4, and 35 ± 10 nmol/g, respectively. These data provide further confirmation that the vitamin B-6 pools in skeletal muscle are resistant to depletion. They also demonstrate that in humans with constant body weight, vitamin B-6 supplementation is not associated with marked increases in vitamin B-6 in muscle.