Bioavailability of vitamin B-6 from wheat bread in humans

Bioavailability of vitamin B-6 from three types of bread was studied in nine men. Each week one of the three types of bread, whole wheat (WHW), white (W) and W enriched with vitamin B-6 (WB6) was fed (570-600 g/day) to each subject using a Latin square design. The WHW, WB6 and W bread supplied 1.20, 1.18 and 0.35 mg of B-6 daily, respectively. The remaining constant diet supplied 0.38 mg of B-6. When W was fed, the subjects also received an oral dose of pyridoxine to maintain a daily intake of 1.5 mg of vitamin B-6. Dietary, urinary, fecal and blood samples were analyzed for vitamin B-6. The predominant forms of vitamin B-6 in the diet and urine were pyridoxine and pyridoxal, respectively. Fecal vitamin B-6 excretion was significantly higher (P smaller than or equal to 0.01) and urinary 4-pyridoxic acid excretion significantly lower (P smaller than or equal to 0.05) when WHW bread was fed than when either WB6 or W bread was fed. The plasma pyridoxal phosphate level was slightly lower when WHW bread was consumed as compared to when WB6 was fed. There were no significant differences in urinary B-6, plasma B-6 or the activity of the erythrocyte transaminases in relation to the type of bread fed. These data suggest that vitamin B-6 is 5-10% less available from WHW than from WB6 or W bread and an oral dose of B-6. The enrichment of refined wheat flour with pyridoxine is feasible based on the nutritional indices determined in this study.