Bioavailable Vitamin Research Articles

Calculated free and bioavailable vitamin D metabolite concentrations in vitamin D-deficient hip fracture patients after supplementation with cholecalciferol and ergocalciferol

We previously showed that oral cholecalciferol and ergocalciferol have comparable effects in decreasing circulating parathyroid hormone (PTH), despite a greater increase in total serum 25-hydroxyvitamin D (25OHD) concentration with cholecalciferol supplementation. However, the effects of cholecalciferol and ergocalciferol on total serum 1,25-dihydroxyvitamin D (1,25(OH)2D), vitamin D-binding protein (DBP), free 25OHD and free 1,25(OH)2D concentrations have not been previously studied.We randomized 95 hip fracture patients (aged 83±8years) with vitamin D deficiency (serum 25OHD <50nmol/L) to oral supplementation with either cholecalciferol 1000IU/day (n=47) or ergocalciferol 1000IU/day (n=48) for three months. All were given matching placebos of the alternative treatment to maintain blinding. We measured serum 25OHD (high-pressure liquid chromatography), 1,25(OH)2D (Diasorin radioimmunoassay), DBP (immunonephelometry), ionized calcium (Bayer 800 ion-selective electrode) and albumin (bromocresol green) concentrations before and after treatment. We calculated free and bioavailable concentrations of the vitamin D metabolites using albumin and DBP, and calculated free vitamin D metabolite indices as the ratios between the molar concentrations of the vitamin D metabolites and DBP.Seventy participants (74%) completed the study with paired samples for analysis. Total serum 1,25(OH)2D did not change significantly with either treatment (p>0.05, post-treatment vs baseline). Both treatments were associated with comparable increases in DBP (cholecalciferol: +18%, ergocalciferol: +16%, p=0.32 between groups), albumin (cholecalciferol: +31%, ergocalciferol: +21%, p=0.29 between groups) and calculated free 25OHD (cholecalciferol: +46%, ergocalciferol: +36%, p=0.08), with comparable decreases in free 1,25(OH)2D (cholecalciferol: −17%, ergocalciferol: −19%, p=0.32 between groups). In the treatment-adherent subgroup the increase in ionized calcium was marginally greater with cholecalciferol compared with ergocalciferol (cholecalciferol: +8%, ergocalciferol: +5%, p=0.03 between groups). There were no significant differences between the treatments in their effects on the calculated bioavailable concentrations or free indices of the vitamin D metabolites (p>0.05 between groups).In vitamin D-deficient hip fracture patients, oral supplementation with cholecalciferol and ergocalciferol had no effect on total serum 1,25(OH)2D, and comparable effects on DBP and free vitamin D metabolite concentrations. This is despite cholecalciferol having greater effects than ergocalciferol in increasing total 25OHD, and in increasing ionized calcium in treatment-adherent subjects. These findings may explain why cholecalciferol and ergocalciferol supplementation result in similar magnitudes of PTH reduction, but implicate potential differences in other vitamin D metabolites, such as 24,25(OH)2D, that could explain their different effects on ionized calcium.

Longitudinal study of vitamin D metabolites after long bone fracture

Animal models suggest a key role for dihydroxylated vitamin D metabolites in fracture healing, as evidenced by increases in serum concentration of 24R,25-dihydroxyvitamin D (24R,25[OH]₂D) after long bone fracture. Human studies investigating the kinetics of serum concentrations of 24R,25[OH]₂D, 1,25-dihydroxyvitamin D (1,25[OH]₂D) and their parent metabolite 25-hydroxyvitamin D (25[OH]D) are lacking. We, therefore, conducted a longitudinal study to determine whether total, free, or bioavailable concentrations of these vitamin D metabolites fluctuate in humans after long bone fracture. Twenty-eight patients with cross-shaft (diaphyseal) long bone fracture presenting to an emergency department in London, UK, were studied. Serum concentrations of 25(OH)D, 24R,25(OH)₂D, 1,25(OH)₂D, vitamin D binding protein, albumin, and calcium were determined within 48 hours of fracture and again at 1 and 6 weeks postfracture. Concentrations of free and bioavailable vitamin D metabolites were calculated using standard equations. No changes in mean serum concentrations of 25(OH)D or 24R,25(OH)₂D were seen at either follow-up time point versus baseline. In contrast, mean serum 1,25(OH)2 D concentration declined by 21% over the course of the study, from 68.5 pmol/L at baseline to 54.1 pmol/L at 6 weeks (p < 0.05). This decline was associated with an increase in mean serum corrected calcium concentration, from 2.32 mmol/L at baseline to 2.40 mmol/L at 1 week (p < 0.001) that was maintained at 6 weeks. No changes in free or bioavailable concentrations of any vitamin D metabolite investigated were seen over the course of the study. We conclude that serum 1,25(OH)₂D concentration declines after long bone fracture in humans but that the serum 24R,25(OH)₂D concentration does not fluctuate. The latter finding contrasts with those of animal models reporting increases in serum 24R,25(OH)₂D concentration after long bone fracture.

Bioavailable vitamin D is more tightly linked to mineral metabolism than total vitamin D in incident hemodialysis patients

Prior studies showed conflicting results regarding the association between 25-hydroxyvitamin D (25(OH)D) levels and mineral metabolism in end-stage renal disease. In order to determine whether the bioavailable vitamin D (that fraction not bound to vitamin D binding protein) associates more strongly with measures of mineral metabolism than total levels, we identified 94 patients with previously measured 25(OH)D and 1,25-dihydroxyvitamin D (1,25(OH)2D) from a cohort of incident hemodialysis patients. Vitamin D binding protein was measured from stored serum samples. Bioavailable 25(OH)D and 1,25(OH)2D were determined using previously validated formulae. Associations with demographic factors and measures of mineral metabolism were examined. When compared with whites, black patients had lower levels of total, but not bioavailable, 25(OH)D. Bioavailable, but not total, 25(OH)D and 1,25(OH)2D were each significantly correlated with serum calcium. In univariate and multivariate regression analysis, only bioavailable 25(OH)D was significantly associated with parathyroid hormone levels. Hence, bioavailable vitamin D levels are better correlated with measures of mineral metabolism than total levels in patients on hemodialysis.

Bioavailable vitamin D in chronic kidney disease

Most of the major vitamin D metabolites 25-hydroxyvitamin D and 1,25-dihydroxyvitamin D circulates in a tightly bound state to vitamin D-binding protein (DBP), rendering this fraction unavailable for biological action. A smaller fraction, loosely bound to albumin or circulating freely, is bioavailable, and hence bioactive. This Commentary discusses the free hormone hypothesis and the role of DBP in vitamin D metabolism.

The Bioavailability of Vitamin E in Fortified Processed Foods

Objectives: Vitamin E is an important human lipophilic antioxidant and is required for many metabolic functions. A high vitamin E intake appears to favorably impact a variety of disease processes. The vitamin E intake, excluding sup-plemental intake, of the vast majority of adults is below the current recommended level. By consuming vitamin E-enriched food, it is possible to take in adequate amounts of vitamin E. Vitamin E intake from enriched foods might prevent certain diseases without the need to ingest specific vitamin E supplements. The vitamin E that is present in enriched foods has to exhibit maximal bioavailability to ensure a sufficient intake of vitamin E from one portion of fortified food. The aim of the present study was to develop an enriched food that has highly bioavailable vitamin E. Furthermore, we wanted to examine whether vitamin E bioavailability can be affected by the technological properties of fortified food. Methods: Volunteers were given test foods (cream cheese and mayonnaise) that had been fortified with 60 mg of RRR-α-tocopherol. The test foods were technologically modified and the bioavailability of RRR-α-tocopherol was determined via a short-term kinetic measurement, which was 24 h long, and a long-term kinetic measurement, which was 28 d long. The test foods were characterized with respect to matrix properties. Results: In comparison to the mayonnaise group the serum α-tocopherol area under the curve (AUC) was significantly higher in the cream cheese group, as shown in the short-term kinetic (p = 0.010) and long-term kinetic (p = 0.017) studies. Conclusions: In conclusion, RRR-α-tocopherol was more bioavailable in cream cheese than in mayonnaise in both short-term and long-term periods. Hence, food matrices affect bioavailability of RRR-α-tocopherol. Fortified foods with proven high α-tocopherol bioavailabilities could be merchandised as functional foods with diseases prevention properties.

Genotype and Environment Effects on the Contents of Vitamins B1, B2, B3, and B6 in Wheat Grain

The total contents of thiamine (vitamin B1), riboflavin (B2), and pyridoxine (B6) and the bioavailable forms of niacin (B3) were determined on wholemeal flours of 24 winter wheat varieties grown on four sites (United Kingdom, Poland, France, and Hungary) in 2007 and of two spring varieties grown on the same sites with the exception of Poland. The contents of vitamins B1 (5.53-13.55 μg/g dw), B2 (0.77-1.40 μg/g dw), and B6 (1.27-2.97 μg/g dw) were within the ranges reported previously, while the content of bioavailable vitamin B3 (0.16-1.74 μg/g dw) was about 10-15% of the total contents of vitamin B3 reported in previous studies. Strong correlations were observed between the contents of vitamins B1, B3, and B6, and partitioning of the variance in the contents of these three B vitamins showed that between 48 and 70% was accounted for by the environment. By contrast, the content of vitamin B2 was not correlated with the contents of other B vitamins, and 73% of the variance was ascribed to the error term, which suggests that this trait may be influenced by genotype × environment interactions. Whereas the contents of vitamins B1, B3, and B6 were correlated positively with the mean temperature from heading to harvest (r > 0.8), the content of vitamin B2 was positively correlated with precipitation during the 3 months prior to heading. These results are discussed in relation to the development of new wheat varieties with enhanced health benefits.

Kinetic Optimization of Folic Acid Polymer Conjugates for Drug Targeting

Problem statement: Folic Acid (FA) is an essential, bioavailable water soluble B-complex vitamin that helps in the replication of normal cells. It is obtained from natural sources and it deficiency can leads to oncogenic cells development. Within this frame work in mind, we designed and synthesized a new bioconjugate carrier that can enhance the effectiveness of FA. Approach: The polymeric carrier: Polysucscinimide (PSI) was synthesized via the polycondensation of aspartic acid by attaching 3-(N,N-Dimethylamino) Propylamine (DMP) and 1,3-Ppropylenediamine (PDA) for solubility behavior and reactivity for FA site anchoring. Also the use of an ester 2-(1H-benzotrial-1-yl)-1,1,3,3-tetramethylurium Hexafluorophosphate (HBTU) as coupling agent to FA. The bioreversible binding of the water-soluble and biocompatible macromolecular were attested through kinetic studies. The kinetic reactions were investigated through the nuclear resonance (H1NMR) spectra analysis. Results and Conclusion: The H1NMR optimization reaction times were found within the range of 120-130 min (80-85%) as optimum coupling. The yield of the FA occurred within the same time range but with maximum incorporation between 90-100%. The growth of FA incorporation in terms of reaction time resulted to an increase inherent viscosity relative to the decrease of water solubility of the conjugate obtained.

Nutrition in vulnerable communities in economically marginalized societies

Childhood malnutrition is highly prevalent in developing countries. Globally 35% (3.5 million) of child deaths before the age of five years were attributed to under nutrition in 2004. Vulnerable communities generally consume a diet based mainly on plant-based staples, and a low consumption of animal source foods, fruit and vegetables predisposes these communities to micronutrient deficiencies. In this paper, South African data is used to illustrate the poor diet and consequences thereof in vulnerable communities. Childhood malnutrition and maternal overweight often co-exist in the same community. Dietary modification strategies to address malnutrition should therefore focus on the nutritional quality of the diet, rather than on energy content only. Animal foods are particularly rich sources of bio-available iron, zinc and vitamin A (the micronutrients of greatest concern), and these nutrients are difficult to obtain in adequate amounts from plant foods alone. Foods of animal sources (particularly muscle tissue) also enhance the absorption of the less bio-available non-heme iron. Dietary modification strategies need to be introduced from a very young age. In the developed world, commercially available baby products play an important role in meeting the nutritional requirements of infants, but in developing countries cost and possible contamination (bottle feeds) prohibit the use of baby products. Addition of small amounts of foods of animal sources can improve the nutritional quality of the diet, as well as the nutritional status and functional outcomes of vulnerable populations. A moderate increase in the consumption of animal source foods will provide critical nutritional benefits without a significant increase in the risk of chronic diseases in the poor. Constraints for frequent consumption of animal source foods include availability, affordability and lack of cold storage facilities. Adequate dietary intake is essential for good nutrition, but frequent infections can also lead to malnutrition. The underlying causes of malnutrition, i.e. inadequate care on the one hand, and insufficient health services and an unhealthy environment on the other hand, should also therefore be addressed.

Vitamin B-12 and neural tube defects: the Canadian experience

Although early epidemiologic studies showed a protective effect of adequate maternal folic acid (FA) status against neural tube defects (NTDs), the role of adequate vitamin B-12 nutrition in the putative reduction of NTD frequency has remained uncertain. Evaluating vitamin B-12 status was complicated by the need to control for altered FA status after fortification in Canada. More recent studies have made use of better biomarkers of vitamin B-12 status, including methylmalonic acid and holotranscobalamin (holoTC). HoloTC provides a useful measure of vitamin B-12 status because it represents the bioavailable fraction of circulating vitamin B-12. By assessing bioavailable vitamin B-12 status in a large Canadian cohort accrued before and after FA fortification, we found a 3-fold increase in the risk of NTDs in mothers who had vitamin B-12 status in the lower quartile, regardless of FA fortification. Our work suggests that vitamin B-12 fortification, analogous to the FA fortification program, may reduce NTDs more than FA fortification alone. A multicenter randomized controlled trial comparing periconceptional vitamin B-12 in combination with FA against FA alone is warranted.

Determinants of Anemia among Preschool Children in the Philippines

Objective: Our objective was to identify the determinants of anemia among rural Filipino children aged 12–71 months.Methods: A cross-sectional survey was conducted among 2090 preschool children from 8 rural villages in Cebu, an area non-endemic for malaria and schistosomiasis. Hemoglobin (Hb) concentration was determined using a HemoCue hemoglobinometer and zinc protoporphyrin (ZPP) concentration was measured with a hematofluorometer. A 3-day non-consecutive 24-hour food recall interview with the child's primary caregiver was done to estimate the child's dietary intake. Stool analysis for presence of soil-transmitted helminths was performed through a concentration technique. A separate interview on household socio-economic status with the child's primary caregiver was conducted.Results: Mean Hb concentration was 12.0 g/dL (SD 1.3). 16.1% were anemic. Age and sex had a significant interaction in their effect on Hb concentration. Females had higher Hb concentration between 12 to 23 months of age. Hb levels equalize between the 2 genders at around 24 months and increase with similar increments until 71 months of age. All dietary parameters improved Hb concentration with increasing intake. In the multiple regression, however, only the index for bioavailable iron and vitamin C intakes remained independent factors. None of the helminths or combination of helminths had significant effects on Hb concentration. Among the socio-economic variables, maternal educational attainment and water supply were significant independent factors. Mean ZPP concentration was 72.07 (SD 46.45) and 30.8% were iron deficient. As with Hb concentration, age and sex had a significant interaction in their effect on ZPP concentration, with females having lower ZPP levels before 24 months of age. Bioavailable iron (animal iron + 0.3*plant iron) had a significant effect on ZPP concentration at levels of at least 15% of the iron requirement. This was seen even after controlling for multivitamin supplementation.Conclusion: The control of anemia among preschoolers can be achieved through a combination of various nutritional interventions such as micronutrient supplementation, food fortification and nutrition education. Our findings emphasize the importance of a multi-sectoral approach to nutritional problems –the importance of empowering women (through engagement and education) and of maintaining a healthy physical environment (water and sanitation) are often peripheral concerns of nutritionists. Our study highlights the importance of supporting initiatives that address these issues not only for their core benefit, but also for the potential benefit to nutrition.

Bioavailability of vitamin A sources for cattle1

An experiment was conducted to evaluate the bioavailability of 5 sources of vitamin A. It was hypothesized that some vitamin A products have protective coatings that are more resistant than others to rumen destruction and that such protection would result in greater tissue concentrations of vitamin A. Fifty-three yearling Angus x Brahman cattle, consisting of 39 steers and 14 heifers, were stratified by BW and sex and randomly assigned to 6 high-concentrate diet groups receiving no vitamin A supplementation (control) or vitamin A supplemented from the following sources: Microvit A (Adisseo, Acworth, GA), Rovamix A (DSM, Parsippany, NJ), Sunvit A, Lutavit A, and Microvit A DLC (Adisseo). The vitamin A treatment groups were fed daily 80,000 IU of retinol/animal in a low-retinol concentrate diet (78.5% oats, 10% cottonseed hulls, 8% molasses, and 2% cottonseed meal; DM basis) and a free-choice, poor quality (low carotene) hay for 84 d. Every 28 d, BW was determined and liver biopsies and plasma were collected and analyzed for retinol concentrations. All retinol treatments showed significant increases in liver retinol concentrations compared with control animals (P < 0.0001), which steadily decreased over time. At all collection times, Microvit A led to numerically, but not significantly, greater concentrations of retinol in liver than did all other treatments. However, at the end of the experiment, there was no significant difference in liver retinol concentration among Microvit A, Rovamix A, Lutavit A, and Microvit A DLC diets. When liver retinol concentrations at all collection times were considered, Microvit A and Rovamix A appeared to provide the most bioavailable vitamin A.

Lycopene and vitamin C concentrations increase in plasma and lymphocytes after tomato intake. Effects on cellular antioxidant protection.

This study seeks to verify whether the regular consumption of small amounts of tomato products can protect lymphocyte DNA and lipids from oxidative damage. Standardized dietary intervention. Twelve healthy female subjects (mean age 25.2 y). Subjects were instructed to follow a standardized diet for 1 week, followed by 3 weeks consumption of the same diet enriched with small amounts of different tomato products providing as a mean 8 mg lycopene, 0.5 mg beta-carotene and 11 mg vitamin C per day. Plasma and lymphocyte concentrations of carotenoids, vitamin C and vitamin E were analysed. Ex vivo protection of lymphocyte DNA from oxidative injury produced by iron ions was evaluated by means of the Comet assay, and lipid peroxidation by HPLC analysis of malondialdehyde (MDA). Dietary intervention with tomato products increased lycopene concentration both in plasma (P < 0.001) and lymphocytes (P < 0.01). Vitamin C concentrations increased by approximately 35% in plasma (P < 0.05) and by approximately 230% in lymphocytes (P < 0.005). Vitamin E decreased significantly in plasma (P < 0.0001) but not in lymphocytes. Finally, there was an improved protection from DNA oxidative damage (P < 0.05) with no significant effect on MDA levels. Our results suggest that tomato products are not only good sources of lycopene but also sources of bioavailable vitamin C. A Regular intake of small amounts of tomato products can increase cell protection from DNA damage induced by oxidant species. This effect may originate from the synergism of different antioxidants present in tomatoes.

Factors associated with Hb concentration in children aged 6-59 months in the State of Pernambuco, Brazil.

In 1997, the prevalence of anaemia was 40.9 % among children aged 6-59 months in the State of Pernambuco, north-east Brazil. Using the same sample of children, we have investigated possible reasons for this high prevalence. A representative sample was selected through a three-stage process: proportional systematic random sampling of municipalities in the State, systematic random sampling of census sectors within these municipalities, and finally, simple random sampling of households with children aged 6-59 months to obtain the sample of 650 children. Data collection included demographic, environmental, socio-economic and maternal variables, and nutritional status and dietary intakes of the children. Multiple linear regression analysis was based on a hierarchical model of factors associated with Hb concentration. The mean Hb concentration of children aged 6-23 months was 10 g/l lower than that of older children. In the regression analysis, child age explained 8.3 % of the variance in Hb concentration. The intake of bioavailable Fe explained a further 3.3, serum retinol 2.7, diarrhoea 2.4, water treatment 1.7, sanitation 1.3 and low birth-weight 0.5 %. The final model explained 23.4 % of the variance in Hb concentration. We conclude that child age, bioavailable-Fe intake, serum retinol concentration, diarrhoea, water treatment, sanitation and low birth-weight are independently associated with Hb concentration. In north-east Brazil, anaemia prevention programmes among children should focus on those aged <2 years and should consider feasible strategies to improve intakes of bioavailable Fe and vitamin A, and reduce infection. Supplemental Fe should be given to low birth-weight infants.

Safety and impact of vitamin A supplementation delivered with oral polio vaccine as part of the immunization campaign in Orissa, India.

A study was carried out in Orissa, India, to evaluate the impact on vitamin A status of vitamin A supplementation integrated with an immunization campaign. Data were collected from a representative sample of 1,811 children, aged 12 to 48 months, at baseline and then at 4 and 16 weeks following implementation of vitamin A supplementation. The primary outcome indicator was serum retinol. The coverage of vitamin A supplementation was 97%. There was a significant decline in the prevalence of Bitot's spots from 2.9% to 1.9% at 4 weeks, but the prevalence increased to 3.6% by 16 weeks. Serum retinol concentrations increased between baseline and 4 weeks (from 0.62 +/- 0.32 to 0.73 +/- 0.23 mumol/L, p < .001) but then decreased to 0.50 +/- 0.19 mumol/l at 16 weeks, which was significantly lower than at baseline (p < .001). The greatest increase in serum retinol from baseline to 4-week follow-up was among children with lowest baseline serum retinol and children with Bitot's spots at baseline. This study demonstrates the short-term benefits of vitamin A supplementation to be significant, especially for those whose status is most compromised. At the same time, the benefit of vitamin A supplementation in this population was transient. The impact of the vitamin A could not be sustained for the full 16 weeks in the study population. This finding calls for exploration of other means to improve vitamin A status, perhaps by adjusting the vitamin A supplementation schedule with more aggressive measures to improve intake of foods rich in bioavailable vitamin A, such as small amounts of animal foods or fortified foods. The study demonstrates the feasibility of integrating vitamin A supplementation with immunization campaigns.

Red Palm Oil Supplementation: A Feasible Diet-Based Approach to Improve the Vitamin A Status of Pregnant Women and Their Infants

This double-blinded, randomized, controlled study was designed to study the effect of dietary supplementation with red palm oil during pregnancy on maternal and neonatal vitamin A status. A total of 170 women were recruited at 16 to 24 weeks of gestation and randomly assigned to an experimental group that received red palm oil to supply approximately one recommended dietary amount (RDA) (2,400 μg) of β-carotene or to a control group that received an equivalent volume of groundnut oil. The women received the oils for a period of 8 weeks, starting at 26 to 28 weeks of gestation and extending to 34 to 36 weeks of gestation. The mean postintervention (34 to 36 weeks) levels of serum retinol were 1.20 ± 0.22 (SD) μmol/L (95% CI, 1.15–1.25) in women receiving red palm oil and 0.73 ± 0.15 μmol/L (95% CI, 0.69–0.77) in their infants; these levels were significantly higher than those in women receiving groundnut oil (1.07 ± 0.26 μmol/L; 95% CI, 1.01–1.13; p &lt; .01) and their infants (0. 62 ± 0.17 μmol/L; 95% CI, 0.57–0.67; p &lt; .001). A significantly lower proportion of women in the red palm oil group than in the control group had vitamin A deficiency (serum retinol levels &lt; 0.7 μmol/L) after intervention (1.5% vs. 9.7%). The proportion of women having anemia was significantly lower (p &lt; .01) in the red palm oil-supplemented group (80.6%) than in the control group (96.7%). The mean birthweight and gestational age of the infants did not differ significantly between the two groups. An increased risk of low birthweight (p = . 003) and preterm delivery (p = . 000) was observed with decreasing serum retinol levels in the third trimester of pregnancy. These results show that red palm oil supplementation significantly improved maternal and neonatal vitamin A status and reduced the prevalence of maternal anemia. Maternal vitamin A status in the later part of pregnancy is significantly associated with fetal growth and maturation. Hence red palm oil, a rich source of bioavailable vitamin A, could be used as a diet-based approach for improving vitamin A status in pregnancy.

Vitamin C is reduced in human milk after storage

In order to establish how cold storage of human milk affects levels of bioavailable vitamin C, 11 samples were stored for 24 h in the refrigerator or up to 2 mo in the freezer. Total vitamin C levels decreased on average by one-third in the refrigerator or after 1 mo of freezing, with wide variations between individuals (6 to 76% and 3 to 100%, respectively). After 2 mo of freezing, the average decrease was two-thirds (7–100%). Conclusion: We recommend a change in human milk storage practices, to under 24 h in a refrigerator or under 1 mo in a freezer. Alternatively, vitamin C supplementation may be considered.

Vitamin C is reduced in human milk after storage

In order to establish how cold storage of human milk affects levels of bioavailable vitamin C, 11 samples were stored for 24 h in the refrigerator or up to 2 mo in the freezer. Total vitamin C levels decreased on average by one-third in the refrigerator or after I mo of freezing, with wide variations between individuals (6 to 76% and 3 to 100%, respectively). After 2 mo of freezing, the average decrease was two-thirds (7-100%). We recommend a change in human milk storage practices, to under 24 h in a refrigerator or under 1 mo in a freezer. Alternatively, vitamin C supplementation may be considered.

Food Sources of Vitamin A and Provitamin a Specific to Africa: An FAO Perspective

Vitamin A deficiency is a major public health problem in Africa, especially in the Sahelian countries. It occurs mainly in young children and women of childbearing age. Inadequate intake of vitamin A is the main cause of the deficiency. The main animal sources of vitamin A are liver, eggs, milk, and milk products. They contain 25 to 8,235 retinol equivalents (RE)/100 g of edible portion. Even though these sources are rich in highly bioavailable vitamin A, their consumption among the population is still low. Plant foods rich in provitamin A represent more than 80% of the total food intake of vitamin A because of their low cost, high availability, and diversity. Fruits, roots, tubers, and leafy vegetables are the main providers of provitamin A carotenoids. Because of their availability and affordability, green leafy vegetables are consumed largely by the poor populations, but their provitamin A activity has been proven to be less than previously assumed. Among fruits, mangoes constitute an important seasonal source of vitamin A. Yellow or orange sweet potatoes are rich in provitamin A. Red palm oil has a high concentration of provitamin A carotenoids (500–700 ppm/100 g). Extension of new varieties with a high content of bioavailable provitamin A and locally adapted education and counseling on the handling and storage of provitamin A sources can significantly increase the vitamin A intake of vulnerable people. The Food and Agriculture Organization has implemented projects in several African countries to increase production and promote consumption of locally produced or available vitamin A–rich foods. The focus has been on women as the principal food producers and behavioral change agents. Adoption of food- and agriculture-based strategies as the best, appropriate, efficient, and long-term solution should be the focus of African efforts to improve nutrition. Food sources of vitamin A and provitamin A are plentiful in Africa. Food-consumption practices, food habits, and cultural aspects represent essential factors to be taken into account for successful implementation of these approaches.

Excess Dietary Methionine Markedly Increases the Vitamin B-6 Requirement of Young Chicks

A soy-protein isolate diet that contained essentially no bioavailable vitamin B-6 was used to establish the quantitative effect of excess dietary methionine on the vitamin B-6 requirement of young chicks. When made adequate in vitamin B-6, chicks fed the basal diet required 2 g/kg supplemental DL-methionine to achieve maximal growth, and 10 g/kg additional DL-methionine (total = 12 g/kg) was found to be a tolerable excess level that would not depress voluntary food intake or growth rate. When chicks were fed seven graded doses of supplemental pyridoxine (PN) in diets that contained either adequate (2 g/kg) or excess (12 g/kg) methionine, the vitamin B-6 requirement for maximal growth was found to increase (P: < 0.01) from 0.73 to 1.05 mg/kg, a 44% increase, when 10 g/kg excess methionine was present in the diet. Indeed, this level of excess dietary methionine depressed (P: < 0.01) growth at all PN dose levels < or =1 mg/kg, but not at PN doses of 1.2 or 1.4 mg/kg. Because dietary intakes of both vitamin B-6 and methionine can affect plasma homocysteine levels, dietary methionine (and protein) intake should be considered important factors in setting safe and adequate requirement levels for vitamin B-6.

Dietary Approaches to the Control of Vitamin A Deficiency: An Introduction and Overview

As a public health problem, deficiency of vitamin A occurs when the habitual intake of bioavailable vitamin A is too little to meet physiological needs under prevailing conditions. Needs are increased during growth periods and when frequent infections cause inefficient utilization of the vitamin. Historical records and recent experience document that improved dietary intake, even when most vitamin A activity comes from provitamin A carotenoids, can correct the problem, especially when such diets contain adequate fat and the subjects are relieved of heavy worm infestation. An epidemiologic evaluation of the entire food chain, consisting of production, procurement, processing, and consumption, provides the framework for selecting suitable dietary approaches. These approaches include homestead food production, centrally or home-based fortified foods, and educational approaches promoting dietary diversification and modification of preparation practices to conserve the vitamin and render it more bioavailable. Even agricultural approaches that select and propagate germ plasma from varieties with increased micronutrient density can be utilized, including, in the future, genetic modifications to increase micronutrient density of vegetable and staple crops. Usually a mixture of intervention strategies will be most effective, particularly when social marketing accompanies efforts to increase consumer acceptance and compliance. Where the ecological and economic context prohibits dietary approaches, or where acute deficiency necessitates an immediate therapeutic response, distribution of vitamin A supplements is needed until suitable food-based approaches become feasible.