Comparative Vitamin B-6 Bioavailability from Tuna, Whole Wheat Bread and Peanut Butter in Humans

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Abstract
Relative bioavailability of vitamin B-6 from tuna, whole wheat bread and peanut butter was investigated in eight men. The study was divided into a 10-day adjustment and three, 14-day experimental periods in a 3 × 3 Latin square design. Vitamin B-6 intake was set at 1.6 mg/day, with 50% of the intake coming from one of the three experimental foods and 50% from a basal diet. Daily complete urine and fecal collections were made. Urine was analyzed for 4-pyridoxic acid (4PA) and vitamin B-6, fecal samples for vitamin B-6 and plasma (sampled every 5 days) for pyridoxal 5′-phosphate (PLP). Mean values ± SD for the adjustment, tuna, whole wheat bread and peanut butter periods were: 5.65 ± 1.76, 4.89 ± 1.10, 3.62 ± 0.66 and 2.80 ± 0.50 µmol/day for 4-pyridoxic acid; 0.98 ± 0.34, 1.05 ± 0.20, 0.76 ± 0.09 and 0.68 ± 0.19 µmol/day for urinary vitamin B-6; 2.72 ± 0.94, 3.08 ± 0.73, 3.80 ± 0.78 and 4.42 ± 1.03 µmol/day for fecal vitamin B-6 and 65.0 ± 23.30, 64.8 ± 29.80, 49.3 ± 14.40 and 48.4 ± 20.20 nM for plasma pyridoxal 5′-phosphate, respectively. 4PA and urinary vitamin B-6 excretion were significantly (P ≤ 0.01) higher in the tuna period than in either the whole wheat bread or peanut butter periods. The fecal vitamin B-6 excretion during the tuna period was significantly lower than during the peanut butter period. The vitamin B-6 in whole wheat bread and peanut butter is 75 and 63%, respectively, as available as that from tuna.