Bioavailability of vitamin B-6 from wheat bread in humans

Comparative bioavailability of vitamins in human foods sourced from animals and plants

Vitamins are essential components of enzyme systems involved in normal growth and function. The quantitative estimation of the proportion of dietary vitamins, that is in a form available for utilization by the human body, is limited and fragmentary. This review provides the current state of knowledge on the bioavailability of thirteen vitamins and choline, to evaluate whether there are differences in vitamin bioavailability when human foods are sourced from animals or plants. The bioavailability of naturally occurring choline, vitamin D, vitamin E, and vitamin K in food awaits further studies. Animal-sourced foods are the almost exclusive natural sources of dietary vitamin B-12 (65% bioavailable) and preformed vitamin A retinol (74% bioavailable), and contain highly bioavailable biotin (89%), folate (67%), niacin (67%), pantothenic acid (80%), riboflavin (61%), thiamin (82%), and vitamin B-6 (83%). Plant-based foods are the main natural sources of vitamin C (76% bioavailable), provitamin A carotenoid β-carotene (15.6% bioavailable), riboflavin (65% bioavailable), thiamin (81% bioavailable), and vitamin K (16.5% bioavailable). The overview of studies showed that in general, vitamins in foods originating from animals are more bioavailable than vitamins in foods sourced from plants.

The Roles of Food Processing in Translation of Dietary Guidance for Whole Grains, Fruits, and Vegetables

The Dietary Guidelines for Americans (DGA) recommend the consumption of whole grains, fruits, and vegetables as part of a healthy diet. However, current consumption patterns suggest that most Americans are not meeting these recommendations. The challenge remains to align the DGA guidance with the food environment and consumers’ expectations for product quality, availability, and affordability. Currently, processed foods play an increasingly important role in American diets. Often characterized as unhealthy, processed foods are contributors to both food and nutritional security. When the alignment of processing strategies with DGA principles exists, achieving DGA goals is more likely, regardless of processing level. In this review, select processing strategies for whole grains, fruits, and vegetables are described to show how DGA principles can guide processing efforts to create healthier products. Although whole grains, supported by industry-wide innovation and guidance, have had some success with consumers, improving intake of fruit and vegetable products remains a challenge. Closing consumption gaps requires new innovations and products aligned with consumer preferences and DGA principles.

Dietary intake of vitamin B6 and concentration of vitamin B6 in blood samples of German vegans

OBJECTIVE

The study aimed to evaluate the dietary vitamin B6 intake and determine the vitamin B6 concentration in blood samples of German vegans.

DESIGN AND SETTING

Cross-sectional study with 33 examination sites all over Germany. Subjects Ninety-three vegans (50 females) with a mean (+/- standard deviation (SD)) age of 43.7 +/- 15.7 years who took no vitamin supplements.

METHODS

Dietary intake was assed using a semi-quantitative food-frequency questionnaire. Erythrocyte aspartate aminotransferase activity coefficient (EAST-AC) was calculated as the ratio of stimulated (pyridoxal 5'-phosphate added) to unstimulated activity in blood samples that were provided after an overnight fast.

RESULTS

Mean +/- SD vitamin B6 intake was 2.83 +/- 0.98 mg day(-1) and mean +/- SD protein intake was 56.6 +/- 21.7 g day(-1). Of the participants 4% showed vitamin B6 intakes lower than daily recommended intakes for Germany, 16% showed EAST-AC > 1.85, and a further 58% showed EAST-AC of 1.5-1-85. Moderate vegans were affected to a lesser extent than strict vegans. None of the established confounders was a significant predictor of EAST-AC. In logistic regression analyses the contribution of nutriments and cereals to pyridoxine intake was the only predictor of EAST-AC classified as < or = 1.85 and > 1.85, respectively.

CONCLUSIONS

In spite of the high total intake of vitamin B6, an adequate concentration in blood samples could not be realised for a majority of the participants. Due to the health implications of a marginal pyridoxine status, vegans should be encouraged to include foods with a high bioavailability of pyridoxine, such as beans, lentils and bananas, in the daily diet.

Effect of dietary fiber on the vitamin B6 status among vegetarian and nonvegetarian elderly (Dutch nutrition surveillance system)

To obtain more insight into the effect of dietary fiber on vitamin B6 status among elderly people, we studied dietary interrelationships as well as associations between dietary intake and plasma pyridoxal-5'-phosphate (PLP) and cofactor stimulation of aspartate aminotransferase in erythrocytes (EAST-AC) among 441 nonvegetarian (aged 65-79) and 32 vegetarian elderly (aged 65-94). EAST-AC was found to be inversely related with intake of vitamin B6 and dietary fiber in bivariate regression analyses. After adjustment for age, intake of energy, protein, and fiber, the intake of vitamin B6 was still inversely related with EAST-AC. The association between EAST-AC and dietary fiber disappeared in the multivariate analysis, whereas total protein intake proved to be positively related with EAST-AC in the multivariate analysis only. The differences between bi- and multivariate analyses are most likely due to the observed interrelationships between intake of vitamin B6, fiber, and protein. It is concluded that dietary fiber does not have a significant impact on the vitamin B6 status among Dutch elderly people, since only protein (positively) and vitamin B6 (inversely) intake appeared to be related with EAST-AC in the multivariate analysis.

The bioavailability of vitamin B6. Recent findings

Further clarification of the bioavailability of dietary vitamin B6 requires better analytical data concerning the forms of vitamin B6 in foods as well as the overall composition of foods. The application of radioisotopic and stable-isotopic studies such as those described will provide useful information concerning the inherent bioavailability of the various vitamin B6 compounds. Additional studies should then address the influence of other dietary components on the utilization of the vitamin B6 compounds, using intrinsic and extrinsic enrichment techniques. Care must be taken in interpretation of the results of animal bioassays in the determination of the bioavailability of vitamin B6 in complex diets.

Refined carbohydrates - a cause of suboptimal nutrient intake

During the refining of carbohydrate foods there is a sharp drop in the concentration of dietary fiber and of various vitamins and minerals. Estimates were made of the effect of refining on the total diet intake of fiber, selenium, folic acid, vitamins E and B6, choline, chromium, magnesium, zinc, manganese, copper, sodium and potassium. The health implications of this are discussed and it is concluded that the losses are likely to be detrimental.