Urinary Excretion Of 4-pyridoxic Acid Research Articles

Vitamin B-6 Status Indices Are Lower in Pregnant than in Nonpregnant Women but Urinary Excretion of 4-Pyridoxic Acid Does Not Differ1–4

The cause of reduced plasma pyridoxal-5'-phosphate (PLP) concentration and the validity of plasma PLP concentration as a vitamin B-6 status indicator during pregnancy are not well understood. In this study, pregnant and nonpregnant women consumed a controlled diet for 5 d to exclude dietary intake as a factor in altered vitamin B-6 metabolic utilization. Plasma PLP and pyridoxal (PL) concentrations were significantly lower and higher, respectively, and plasma PL+PLP concentration was significantly lower during pregnancy. When plasma PLP and PL concentrations were normalized based on plasma albumin concentration, the differences were less marked but were still significant. The erythrocyte aspartate aminotransferase activity coefficient was significantly greater in pregnant women which is a further indication of reduced vitamin B-6 concentrations in the blood. No difference was observed in the urinary excretion of 4-pyridoxic acid between the pregnant and nonpregnant women. Results of this study demonstrate that vitamin B-6 status indices are lower during pregnancy without differences in the urinary excretion of 4-pyridoxic acid.

Vitamin B6Requirement: Indicators and Factors Affecting

The purpose of this study was to establish the selection of indicators for estimating and factors affecting the requirement of vitamin B6. There has been a need to establish the human requirements of vitamin since vitamin is thought to be involved in more than one hundred biochemical reactions as a coenzyme in the metabolism of amino acids, glucose, and lipid, and the synthesis of neurotransmitters. For the review of the literature, this study included from early findings of the sixties to studies of 2009. This study suggests that plasma pyridoxal 5' phosphate (PLP) is the best single indicator of vitamin status for the healthy but not for the non-healthy. Erythrocyte aspartate aminotransferase and alanine aminotransferase activation by PLP as an indirect measure and urinary 4-pyridoxic acid excretion as a direct measure are useful as supporting indicators. Bioavailability, nutrient interaction, physiological need, and chronic diseases may increase the requirement for vitamin . However, these effects can not be quantified due to insufficient evidences.

Inflammation causes tissue-specific depletion of vitamin B6

Previously we observed strong and consistent associations between vitamin B6 status and several indicators of inflammation in patients with rheumatoid arthritis. Clinical indicators, including the disability score, the length of morning stiffness, and the degree of pain, and biochemical markers, including the erythrocyte sedimentation rate and C-reactive protein levels, were found to be inversely correlated with circulating vitamin B6 levels. Such strong associations imply that impaired vitamin B6 status in these patients results from inflammation. In the present study we examined whether inflammation directly alters vitamin B6 tissue contents and its excretion in vivo. A cross-sectional case-controlled human clinical trial was performed in parallel with experiments in an animal model of inflammation. Plasma and erythrocyte and pyridoxal 5'-phosphate concentrations, urinary 4-pyridoxic acid excretion, and the activity coefficient of erythrocyte aspartate aminotransferase were compared between patients and healthy subjects. Adjuvant arthritis was induced in rats for investigating hepatic and muscle contents as well as the urinary excretion of vitamin B6 during acute and chronic inflammation. Patients with rheumatoid arthritis had low plasma pyridoxal 5'-phosphate compared with healthy control subjects, but normal erythrocyte pyridoxal 5'-phosphate and urinary 4-pyridoxic acid excretion. Adjuvant arthritis in rats did not affect 4-pyridoxic acid excretion or muscle storage of pyridoxal 5'-phosphate, but it resulted in significantly lower pyridoxal 5'-phosphate levels in circulation and in liver during inflammation. Inflammation induced a tissue-specific depletion of vitamin B6. The low plasma pyridoxal 5'-phosphate levels seen in inflammation are unlikely to be due to insufficient intake or excessive vitamin B6 excretion. Possible causes of decreased levels of vitamin B6 are discussed.

Vitamin B6 metabolites in idiopathic calcium stone formers: no evidence for a link to hyperoxaluria.

Vitamin B6 metabolites and their potential correlates to urinary oxalate excretion in idiopathic calcium stone formers (ICSF) compared with healthy subjects were investigated. This clinical study was performed in a population of male ICSF with (Hyperoxalurics, n=55) or without hyperoxaluria (Normooxalurics, n=57) as well as in 100 healthy male control subjects. Pyridoxal 5'-phosphate serum concentration (S-pyridoxal 5'P) and 24-h urinary excretion of 4-pyridoxic acid (U-4pyridoxic acid) were measured using HPLC; 24-h urinary excretion of oxalate (U-oxalate) was measured concurrently. A subgroup of subjects (40 Hyperoxalurics, 15 Normooxalurics and 50 controls) underwent the same measurements before and after 7-day pyridoxine loading per os (pyridoxine hydrochloride, 300 mg/d). Under usual conditions, U-4pyridoxic acid was similar in the three groups, whereas mean S-pyridoxal 5'P was significantly lower ( p<0.0001) in the Hyperoxalurics (59.6+/-21.2 nmol/L) and in the Normooxalurics (64.9+/-19.7 nmol/L) than in the controls (86.0+/-31.0 nmol/L). No correlation could be found between U-oxalate and U-4pyridoxic acid or S-pyridoxal 5'P. After B6 loading, S-pyridoxal 5'P was still significantly lower in the Hyperoxalurics (415+/-180 nmol/L, p<0.001) and in the Normooxalurics (429+/-115 nmol/L, p=0.036) than in the controls (546+/-180 nmol/L), although there was no difference between groups for U-4pyridoxic acid. No correlation in any group could be found between changes in U-oxalate and changes in U-4pyridoxic acid or S-pyridoxal 5'P. Although there is no vitamin B6 deficiency in ICSF with or without hyperoxaluria, these patients, on average, have lower levels of S-pyridoxal 5'P than healthy subjects. However, this slight decrease does not seem to account for idiopathic hyperoxaluria.

The Influence of Dietary Restriction on Vitamin B-6 Vitamer Distribution and on Vitamin B-6 Metabolizing Enzymes in Rats

Objective: The purpose of this study was to assess the effect of dietary restriction on tissue distribution of vitamin B-6 vitamers and activities of vitamin B-6 metabolizing enzymes in rats.Methods: Male rats were subjected to a 40% dietary restriction for 10, 20 or 40 weeks. The tissue vitamin B-6 vitamer concentrations and activities of the vitamin B-6 metabolizing enzymes of the animals were determined.Results: The plasma pyridoxal 5′-phosphate (PLP) concentrations of the diet-restricted (DR) rats were comparable to those of the control group at week ten but were significantly lower at weeks 20 and 40. These significantly lower levels of plasma PLP in DR rats might in part be related to lower hepatic pyridoxal kinase and pyridoxamine (pyridoxine) 5′-phosphate oxidase activities. The urinary 4-pyridoxic acid excretion of the DR groups responded to the reduced food intake and were lower at weeks 10 and 20. Tissue levels of PLP were not affected by dietary restriction. In contrast, greater levels of pyridoxamine 5′-phosphate were found in liver, kidney and heart of the DR animals.Conclusion: The duration of dietary restriction influenced the distribution of vitamin B-6 vitamers. When plasma PLP is used to evaluate vitamin B-6 status, the length of dietary restriction should be considered.

Konjac mannan improves the vitamin B-6 status of rats fed a vitamin B-6-deficient diet.

To investigate how dietary fiber in the diet affects vitamin B-6 nutriture of rats which have been deprived of vitamin B-6, rats were made vitamin B-6-deficient by feeding a vitamin B-6-deficient 70% casein diet. They were fed 2% cellulose powder-based vitamin B-6-deficient diets supplemented with 3% of additional dietary fiber sources (agar, konjac mannan, pectin and cellulose powder) for subsequent 18 days. Vitamin B-6 status was evaluated according to several biological criteria (weight gain, urinary excretion of xanthurenic acid after tryptophan loading, plasma pyridoxal 5'-phosphate, apparent pyridoxal 5'-phosphate-saturation of liver kynureninase, urinary excretion of 4-pyridoxic acid and fecal output of vitamin B-6). Vitamin B-6 status evaluated by these criteria was considerably improved in the konjac mannan-fed group, when compared with the respective data of the vitamin B-6 supplemented group. The relative mean effect of the konjac mannan diet was about 40% of the vitamin B-6 supplemented diet. In conclusion, konjac mannan was effective for improving the vitamin B-6 nutritional state in vitamin B-6-deprived rats.

Changes in vitamin B-6 status indicators of women fed a constant protein diet with varying levels of vitamin B-6

Changes in vitamin B-6 status indicators were evaluated in vitamin B-6-replete subjects. Ten young women consumed diets providing 85 g protein/d and 1.03, 1.33, 1.73, and 2.39 mg vitamin B-6/d for 12 or 15 d during four successive diet periods; in a second study, six women were fed diets providing 85 g protein/d and 0.84, 1.14, and 2.34 mg vitamin B-6/d for 10 or 12 d during three successive diet periods. Vitamin B-6 status indicators showing significant differences among intakes included urinary excretion of 4-pyridoxic acid and total vitamin B-6, pyridoxal 5'-phosphate and total vitamin B-6 in plasma, and xanthurenic acid excretion after a 2-g L-tryptophan load. Significant correlations were found between vitamin B-6 intake and 4-pyridoxic acid, total vitamin B-6, plasma pyridoxal 5'-phosphate, plasma total vitamin B-6, erythrocyte alanine aminotransferase percentage stimulation and postload excretion of xanthurenic acid and volatile amines (kynurenine plus acetylkynurenine). Depending on the indicator, between 20% and 70% of the subjects had inadequate values for 4-pyridoxic acid, total vitamin B-6, plasma pyridoxal 5'-phosphate, and erythrocyte alanine aminotransferase percentage stimulation at a vitamin B-6 intake of 1.33 mg/d (0.016 mg vitamin B-6/g protein). A ratio of dietary vitamin B-6 to protein > 0.016 mg/g is required for adequate vitamin B-6 status in women.

Chronic Exercise Affects Vitamin B-6 Metabolism but Not Requirement of Growing Rats , ,

The effect of chronic exercise (forced swimming) on vitamin B-6 status and metabolism was studied in growing male rats fed deficient (0 mg pyridoxine-HCl/kg), suboptimal (2 mg pyridoxine-HCl/kg) or control (7 mg pyridoxine-HCl/kg) diets for 9 wk. Sedentary rats were fed the same diets. Body weight gain was lower in deficient rats than in both other dietary groups. Sedentary rats were heavier than trained rats of all diet groups. Erythrocyte aspartate aminotransferase, urinary 4-pyridoxic acid excretion, blood (plasma and erythrocytes) and tissue B-6 vitamers were measured. Urinary 4-pyridoxic acid, plasma pyridoxal 5′-phosphate and erythrocyte aspartate aminotransferase values of exercised and sedentary rats responded to changes in dietary pyridoxine but were not different from one another. After 9 wk of vitamin B-6 depletion, tissue concentrations of pyridoxal 5′-phosphate and pyridoxamine 5; 5'-phosphate were 41–66% and 26–49% lower, respectively, in the deficient groups than in the control groups. Larger percentage differences occurred in plasma than in tissues (95 vs. 22–66%). In liver, pyridoxal 5′-phosphate concentrations were lower, whereas pyridoxal concentrations were higher in trained than in sedentary rats. In gastrocnemius muscle, pyridoxal 5′-phosphate, pyridoxamine 5′-phosphate and total vitamin B-6 concentrations were higher in trained than in sedentary rats. Concentrations of vitamin B-6 compounds in heart, kidneys, brain and adrenals were not affected by training. On the basis of the vitamin B-6–dependent variables measured in this study, we conclude that prolonged exercise affects the metabolism of vitamin B-6, but does not increase the vitamin B-6 requirement in growing rats.

Pyridoxic acid excretion during low vitamin B-6 intake, total fasting, and bed rest

Vitamin B-6 metabolism in 10 volunteers during 21 d of total fasting was compared with results from 10 men consuming a diet low only in vitamin B-6 (1.76 mumol/d) and with men consuming a normal diet during bed rest. At the end of the fast mean plasma concentrations of vitamin B-6 metabolites and urinary excretion of 4-pyridoxic acid tended to be higher in the fasting subjects than in the low-vitamin B-6 group. The fasting subjects lost approximately 10% of their total vitamin B-6 pool and approximately 13% of their body weight. The low-vitamin B-6 group lost only approximately 4% of their vitamin B-6 pool. Compared with baseline, urinary excretion of pyridoxic acid was significantly increased during 17 wk of bed rest. There was no increase in pyridoxic acid excretion during a second 15-d bed rest study. These data suggest the possibility of complex interactions between diet and muscle metabolism that may influence indexes that are frequently used to assess vitamin B-6 status.

Relative bioavailability of B-6 vitamers from cooked ground beef in humans

The relative bioavailability of vitamin B-6 from cooked beef, supplemented with pyridoxal (PL) or pyridoxamine (PM), was investigated in two groups of healthy young men (age 22–35 years). The subjects were fed a controlled diet (2100–2500 kcal/day) for four days during the two test periods. After two days of controlled dietary intake, subjects ingested equimolar amounts of PL (5.98 μmol) or PM (5.95 μmol) in apple juice or cooked beef (176 0 C, 75 mins). After vitamin B-6 dosage, 24 hr urine samples were collected. In vitro assays revealed an increase in the irreversible binding (15–20%) of the [ 3H]B-6 vitamers to proteins in cooked beef extrinsically labelled with [ 3H]PL or [ 3H]PM compared to their respective controls in apple juice. There was no difference in the urinary excretion of 4-pyridoxic acid (4-PA) when subjects consumed the vitamin in apple juice or in cooked beef. Furthermore, urinary 4-PA excretion was not significantly different between the groups supplemented with PL or PM in the cooked test samples. In conclusion, vitamin B-6 from cooked beef appears to be highly bioavailable despite the increased irreversible binding of B-6 vitamers to proteinaceous components in beef.

Effect of sulfasalazine on vitamin B-6 status and metabolism in vitamin B-6adequate and deficient rats

Diets adequate or deficient in vitamin B-6 were supplemented or not supplemented with sulfasalazine and fed to rats for 5 weeks. After that time period, 24 hour urine samples were collected, rats were sacrificed, and liver and blood samples were collected. During the 5 week feeding period, reduced weight gain was observed for rats fed the deficient diet supplemented with sulfasalazine compared to deficient controls. There was no difference in the plasma pyridoxal 5′-phosphate (PLP) concentrations, plasma or red blood cell aspartate aminotransferase activity, and urinary excretion of 4-pyridoxic acid between the deficient control rats and deficient rats fed sulfasalazine. Hepatic PLP concentrations were lower in deficient rats fed sulfasalazine compared to the deficient controls. Observations from this study would suggest that sulfasalazine intake may aggravate a vitamin B-6 deficiency.

Relationship Between Vitamin B-6 Status and Elevated Pyridoxal Kinase Levels Induced by Theophylline Therapy in Humans

Theophylline administration to seven healthy male volunteers resulted in a rapid and significant decline in both plasma and erythrocyte pyridoxal-5'-phosphate levels. Total erythrocyte pyridoxal kinase levels increased during 15 wk of theophylline treatment from a mean initial activity of 19.23 +/- 5.03 (mean +/- SD) to 62.64 +/- 11.59 nmol pyridoxal-5'-phosphate formed/(g hemoglobin.h). Although plasma pyridoxal levels remained normal, the threefold increase in total erythrocyte pyridoxal kinase activity levels did not normalize plasma and erythrocyte pyridoxal-5'-phosphate levels. Pyridoxal-5'-phosphate hydrolysis was not affected by theophylline therapy. Increased pyridoxal oxidation was confirmed by elevated urinary 4-pyridoxic acid excretion after 15 wk of theophylline treatment. Mean erythrocyte alanine aminotransferase activity declined by 70%, and aspartate aminotransferase activity declined by 50%, indicating that decreased availability of pyridoxal-5'-phosphate can have widespread metabolic consequences. We conclude that the effect of theophylline on vitamin B-6 metabolism is not transitory and cannot be overcome by elevated intracellular levels of pyridoxal kinase. However, pyridoxine supplementation (10 mg/d for 1 wk) normalized indices of vitamin B-6 status and reversed the downward trend in both alanine aminotransferase and aspartate aminotransferase activity levels.

Vitamin B6 status in cirrhotic patients in relation to apoenzyme of serum alanine aminotransferase

Plasma levels of pyridoxal-5'-phosphate (PLP) in cirrhotic patients were significantly lower than in control subjects. However, the plasma total pyridoxal level and urinary 4-pyridoxic acid excretion were not decreased in non-alcoholic patients but in alcoholic patients. In the latter, the percentage of apo alanine aminotransferase was not related to the plasma PLP level, but was significantly correlated with plasma total pyridoxal level and urinary 4-pyridoxic acid excretion. We conclude that alcoholic cirrhotic patients have vitamin B6 deficiency, which is at least responsible for low serum alanine aminotransferase activity.

Bioavailability of Vitamin B-6 from Rat Diets Containing Wheat Bran or Cellulose

Bioavailability of vitamin B-6 (B-6) in the total diet was studied in male, weanling Sprague-Dawley rats fed fiber-free (FF) diets with 0.2 or 6.9 mg pyridoxine/kg diet (0-, 2- or 6.9-PYR), 20% wheat bran (WB) diets with 3.9- or 5.5-PYR or 7% cellulose (C) diets with 0- or 2-PYR for 28 d. Body weight gain (mean +/- SEM) with 0-PYR was 70 +/- 9.0 and 81.2 +/- 4.2 g for FF and C, respectively. All other groups gained 170-180 g. Urinary excretion of 4-pyridoxic acid (4-PA), a major B-6 metabolite, for FF groups was 1.31 +/- 0.22, 2.26 +/- 0.28 and 6.39 +/- 1.73 micrograms/24 h, at 0-, 2- and 6.9-PYR, respectively. Rats fed WB diets excreted 4.99 +/- 0.58 and 9.81 +/- 0.76 micrograms/24 h (3.9- and 5.5-PYR, respectively) and those fed C diets excreted 1.46 +/- 0.34 and 2.69 +/- 0.72 micrograms/24 h (0- and 2-PYR). There was increasing turnover and shorter biological half-life of [14C]pyridoxine (1 mu Ci injected on d 1) with increasing dietary B-6. Growth, 4-PA and 14C turnover data indicated that WB contributed to B-6 intake of these rats. Cellulose acted as a simple dietary diluent and had no effect on indices of B-6 status. These data suggest that dietary fiber, as cellulose or the indigestible component of wheat bran, does not adversely affect the bioavailability of vitamin B-6.

Effect of exposure to carbon disulfide on tryptophan metabolism and the tissue vitamin B6 contents of rats.

Female Wistar rats were exposed to 100 ppm or 600 ppm carbon disulfide for 6 hours a day, 5 days a week for 12 weeks. During the exposure period, their urinary excretion of 4-pyridoxic acid was determined. The urinary excretions of xanthurenic acid and kynurenic acid after tryptophan loading were also determined. At the end of the exposure period, the rats were sacrificed and the levels of the five major forms of vitamin B6, pyridoxine, pyridoxal, pyridoxamine, pyridoxal phosphate and pyridoxamine phosphate, in the liver, kidneys and brain were determined by HPLC fluorometry. During the exposure the urinary excretions of xanthurenic acid and kynurenic acid after i.p. administration of tryptophan increased significantly in both experimental groups. However, urinary excretion of 4-pyridoxic acid decreased only slightly in the group exposed to carbon disulfide at 600 ppm and did not decrease in the group exposed to 100 ppm carbon disulfide. Furthermore, no significant changes were observed in the contents of vitamins B6 in any tissues examined. These results indicate that carbon disulfide does not cause vitamin B6 deficiency and thus that the disorders of tryptophan metabolism induced by carbon disulfide intoxication are not due to vitamin B6 deficiency.

Determination of urinary 4-pyridoxic acid levels as 4-pyridoxic acid lactone using high-performance liquid chromatography

A high-performance liquid chromatography method for quantitation of urinary 4-pyridoxic acid excretion is presented. Urine samples were treated with HCl to form 4-pyridoxic acid lactone. Acid-treated urine samples were diluted and analyzed by cation-exchange chromatography involving post-column alkalinization and fluorescence detection. Absence of interfering fluorescent urinary compounds was demonstrated by 1) analyzing urine samples without lactonization and 2) rechromatography of aliquots of 4-pyridoxic acid lactone peaks employing reverse-phase chromatography. The method is suitable for determination of urinary 4-pyridoxic acid excretion in nutritional, metabolic, and pharmacokinetic studies.

Urinary 4-pyridoxic acid excretion in 24-hour versus random urine samples as a measurement of vitamin B6 status in humans

Urinary excretion of 4-pyridoxic acid (4PA) in 19 men (n = 5) and women (n = 14) was measured to evaluate the validity of determining the 4PA/creatinine ratio in random urine samples as an alternative to total 24-h 4PA excretion in assessing vitamin B6 nutritional status. The relationships among dietary vitamin B6 intake, 4PA excretion, plasma pyridoxal 5′-phosphate levels, and erythrocyte aspartate aminotransferase activity and in vitro stimulation by added plasma pyridoxal 5′-phosphate were examined. The subjects consumed all meals for 3 days in a metabolic unit, and protein intake was kept constant. Plasma pyridoxal 5′-phosphate concentration was positively correlated with vitamin B6 intake of the previous day (r = 0.61, p < 0.01). There was a positive correlation (r = 0.59, p < 0.01) between total 4PA and 4PA/ creatinine in the 24-h urine samples. No difference (p > 0.05) in 4PA/creatinine between the 24-h samples and either morning or afternoon random samples taken the next day was found. These findings support the use of the 4PA/creatinine ratio in random urine samples as an alternative to 24-h urinary 4PA excretion.

Increased plasma pyridoxal 5′-phosphate and vitamin B6 in male adolescents after a 4500-meter run

To investigate the effect of running on vitamin B6 metabolism, plasma pyridoxal 5′-phosphate and total vitamin B6 levels were determined in male adolescent trained athletes before and immediately after a 4500-m run. Six to seven subjects were studied twice during the fall and once during the spring training seasons. A mean increase in pyridoxal 5′-phosphate of 0.77 ± 0.31 to 1.83 ± 0.77 nmol/100 ml of plasma was observed after the three runs (p < 0.01). Similarly, significant increases (p < 0.05) in plasma total vitamin B6 were seen in all three runs. These increases were not solely due to changes in plasma volume. From urine samples collected on two runs, urinary 4-pyridoxic acid excretion in this group of adolescents was found to be similar to that reported for male adults. While changes in plasma glucose were not significantly correlated with changes in vitamin B6 metabolites, it is hypothesized that the significant changes in vitamin B6 metabolites found in this study were related to an increased need for cofactor for gluconeogenesis. The changes found in this study do not provide evidence for or against an increased need for vitamin B6 in persons that exercise, but does show, for the first time, that exercise in the form of long distance running dramatically alters plasma levels of pyridoxal 5′-phosphate.

Effects of oestrogen administration on vitamin B6 and tryptophan metabolism in the rat.

1. In order to assess the effects of oestrogens on the metabolism of tryptophan and vitamin B6, ovariectomized rats have been maintained on diets providing known amounts of tryptophan, nicotinamide and vitamin B6. They received oestrone sulphate, 210 micrograms/kg body-wt per d, either incorporated in the diet for 8 weeks, or by daily intraperitoneal injection for periods of 1-3 d. 2. Oestrone sulphate administration caused a slight reduction in the concentration of pyridoxal phosphate in plasma. It had no effect on the concentration of pyridoxal phosphate in liver or kidney, the urinary excretion of 4-pyridoxic acid, the activation of erythrocyte aspartate aminotransferase (L-aspartate:2-oxo-glutarate aminotransferase, EC 2. 6. 1. 1) by incubation with added pyridoxal phosphate, or the activity of pyridoxal oxidase (aldehyde:oxygen oxido-reductase, EC 1.2.3.1) in the liver. 3. Oestrone sulphate administration caused an increase in the urinary excretion of kynurenine and a reduction in the activity of liver kynureninase (L-kynurenine hydrolase, EC 3.7.1.3). It had no effect on the urinary excretion of N1-methyl nicotinamide or the concentrations of nicotinamide nucleotides in blood, liver or kidney. 4. There was a considerable excess of the apoenzyme of kynureninase in the liver. Incubation of liver homogenates with added pyridoxal phosphate led to a 4- to 5-fold increase in activity. 5. We conclude that there is no evidence of any significant effect of oestrogens on vitamin B6. It is suggested that abnormalities of tryptophan metabolism in women receiving oestrogens, which have been widely attributed to drug-induced vitamin B6 depletion, can be accounted for by inhibition of kynureninase by oestrogen metabolites.

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.