Graduate Thesis Or Dissertation
 

In vivo and in vitro assessment of vitamin B6 bioavailability in humans

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  • Bioavailability (BA) of vitamin B6 (B-6) from foods may be limited. The knowledge of the BA of B6 from food is important in that this would help to understand if the B6 present in the diet of individuals will meet the requirements for this vitamin. The purpose of this study was a) to develop a method to measure the level of glycosylated vitamin B6 (GB6) in the foods; b) to investigate the relative vitamin B6 bioavailability from tuna (T), whole wheat bread (WW), and peanut butter (PB) in humans; c) to follow the excretion pattern of GB6 and relate this to the occurrence of the GB6 in foods. To measure the level of GB6 in foods, the B6 content was determined microbiologically before and after treatment of the foods with β-glycosidase as well as after acid hydrolysis. Animal products contained no measurable amount of GB6, but grain and legumes had 6-75% of total B6 present as GB6. Of the fruits and vegetables analyzed, orange juice (47%) and raw carrots (51%) had the highest GB6 levels. Relative BA of B6 from T, WW, and PB was investigated in eight healthy men in a 52-day study (10-day adjustment and three 14-day experimental periods). B5 intake was set at 1.6 mg/day, with 50% coming from one experimental food and 50% from a basal diet. Urine was analyzed for 4-pyridoxic acid (4PA) and B6; feces for B6; and plasma for pyridoxal-5'-phosphate (PLP). Of these four indices used to assess B6 bioavailability, 4PA and urinary B6 were significantly (p < 0.01) higher in T than in either WW or PB periods. When T was fed, fecal B6 excretion was significantly (p < 0.01) lower than when PB was fed. The B6 in WW and PB was 75% and 63% as available as that from T, respectively. The urine from the last day of each period for five subjects and the last fecal composite for each period was analyzed for the nonconjugated B6 and GB6. The majority of B6 in the feces was in the non-conjugated form. No GB6 was detected in the feces during either the T or PB periods. Only 4% of total B6 in the feces was in the GB6 form when WW was fed. GB6 was found in the urine in all periods. The level of GB6 in the food was inversely related to B6 bioavailability in foods fed to humans in our study and in three other human studies. It appears that the level of GB6 in foods could be used as an index of B6 bioavailability in foods.
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