Vitamin A Stores Research Articles

Development of a “Super‐Kid” Model Based on Plasma [13c10]‐Retinol Kinetics in Well‐Nourished Mexican Infants

To study vitamin A (VA) metabolism in infants, a tracer dose of [13C10]‐retinyl acetate was given orally to 15 subjects (15‐34 months), 2 samples were drawn/child to build a 10 time‐point kinetic curve from 7.5 h to 35 d after dosing; mean fraction of dose in plasma was calculated at each sampling time. Model‐based compartmental analysis using WinSAAM was used to develop a composite 'super‐kid’ model of plasma [13C10]‐retinol kinetics. Data fit a 5 compartment model which includes a delay element representing VA digestion and absorption plus chylomicron formation and metabolism; a compartment for uptake and metabolism of newly absorbed VA in liver; the plasma retinol pool; and two extravascular VA storage pools: a fast‐ and a slower turning‐over compartment. Irreversible loss was modeled from the slower turning‐over pool, at a rate of 2.6% per day, which is the system fractional catabolic rate (FCR). Our modeling results indicate early and rapid VA absorption, followed by significant retinol recycling among plasma and tissues and high retinol turnover, plus a low system FCR reflecting the relatively high VA stores in these well‐nourished infants who received a 60 mg retinyl acetate dose as part of a National Program in Mexico, 3 mo prior to this study. The 'super kid’ approach facilitates model development in infants for whom blood collections need to be minimized or when access to subjects is limited in the field.IAEA 16880

Quantifying the Bioefficacy of β‐Carotene‐biofortified Sorghum Using a Mongolian Gerbil Model

β‐Carotene‐biofortified transgenic sorghum is being developed to alleviate vitamin A deficiency in semiarid regions of Africa. Our objective was to quantify the bioefficacy of the biofortified sorghum using a Mongolian gerbil model. Gerbils were fed a vitamin A (VA)‐free control diet (45% by wt non‐transgenic sorghum flour) for 4 wk; 8 animals were then killed at baseline. The remaining animals were randomly assigned to treatments for 6 wk (n = 11 per group): 1) control diet dosed daily with cottonseed oil vehicle; 2) biofortified diet (45% by wt transgenic sorghum flour) dosed daily with cottonseed oil vehicle (95.8 nmol retinol equivalents/d); 3) control diet dosed daily with β‐carotene (84.5 nmol retinol equivalents/d); 4) control diet dosed daily with VA (84.5 nmol retinol equivalents/d). Liver VA stores in the baseline (1.27 ± 0.29 μmol), β‐carotene‐dosed (1.30 ± 0.26 μmol), and biofortified (1.31 ± 0.23 μmol) groups were not different; liver stores in the vehicle‐dosed control group were lower (0.92 ± 0.22 μmol) (P < 0.03). Liver stores were highest in the VA‐dosed group (2.48 ± 0.23 μmol) (P < 0.0001). The calculated bioconversion efficiency for the β‐carotene in the biofortified sorghum (4.3 μg β‐carotene to 1 μg retinol) was similar to that of the β‐carotene dose (3.8 μg to 1 μg retinol). The β‐carotene in the biofortified sorghum effectively restored liver vitamin A stores in an animal model.

International experiences in assessing vitamin A status and applying the vitamin A-labeled isotope dilution method.

Inadequate vitamin A (VA) nutrition continues to be a major problem worldwide, and many interventions being implemented to improve VA status in various populations need to be evaluated. The interpretation of results after an intervention depends greatly on the method selected to assess VA status. To evaluate the effect of an intervention on VA status, researchers in Cameroon, India, Indonesia, Mexico, Senegal and Zambia have used serum retinol as an indicator, and have not always found improvement in response to supplementation. One problem is that homeostatic control of serum retinol may mask positive effects of treatment in that changes in concentration are observed only when status is either moderately to severely depleted or excessive. Because VA is stored mainly in the liver, measurements of hepatic VA stores are the “gold standard” for assessing VA status. Dose response tests such as the relative dose response (RDR) and the modified relative dose response (MRDR), allow a qualitative assessment of VA liver stores. On the other hand, the use of the vitamin A-labeled isotope dilution (VALID) technique, (using 13C or 2H-labeled retinyl acetate) serves as an indirect method to quantitatively estimate total body and liver VA stores. Countries including Cameroon, China, Ghana, Mexico, Thailand and Zambia are now applying the VALID method to sensitively assess changes in VA status during interventions, or to estimate a population’s dietary requirement for VA. Transition to the use of more sensitive biochemical indicators of VA status such as the VALID technique is needed to effectively assess interventions in populations where mild to moderate VA deficiency is more prevalent than severe deficiency.

Relative vitamin A values of 9-cis- and 13-cis-β-carotene do not differ when fed at physiological levels during vitamin A depletion in Mongolian gerbils (Meriones unguiculatus)

Provitamin A biofortification of staple crops may decrease the prevalence of vitamin A (VA) deficiency if widely adopted in target countries. To assess the impact of processing methods on the VA value of plant foods, the unique bioefficacies of cis-βC isomers (formed during cooking) compared with all-trans (at) β-carotene (βC) must be determined. The bioefficacies of 9-cis (9c)- and 13-cis (13c)-βC isomers were compared with those of the at-βC isomer and VA positive (VA+) and negative (VA - ) controls in VA-depleted Mongolian gerbils (Meriones unguiculatus) in two experimental studies (study 1, n 56; study 2, n 57). A 3- or 4-week depletion period was followed by a 3- or 4-week treatment period in which the groups received oral doses of the 9c-, 13c- or at-βC isomers in cottonseed oil (study 1, 15 nmol/d; study 2, 30 nmol/d). In study 1, the βC isomers did not maintain baseline liver VA stores in all groups (0.69 (SD 0.20) μmol/liver) except in the VA+group (0.56 (SD 0.10) μmol/liver) (P= 0.0026). The βC groups were similar to the VA+group, but the 9c- and 13c-βC groups did not differ from the VA - group (0.39 (SD 0.09) μmol/liver). In study 2, the βC isomers maintained baseline liver VA stores in all the βC groups (0.35 (SD 0.13) μmol/liver), and in the VA+group, the VA supplement (0.54 (SD 0.19) μmol/liver) exceeded the baseline VA status (0.38 (SD 0.15) μmol/liver) (P< 0.0001); however, the 9c-βC group did not differ from the VA - group (0.20 (SD 0.07) μmol/liver). In vivo isomerisation of βC was confirmed in both experimental studies. Lower VA bioconversion factor values were obtained for the cis-βC isomers in study 2 when compared with study 1, but higher values were obtained for the at-βC isomer. Dose and VA status clearly affect bioconversion factors. In conclusion, the cis-βC isomers yielded similar liver VA stores to the at-βC isomer in Mongolian gerbils, and liver VA stores of the 9c- and 13c-βC groups did not differ when the doses were provided at physiological levels over time in two studies.

Simplified approaches for estimating vitamin A stores and β‐carotene bioconversion in humans (39.6)

Better methods are needed to assess vitamin A (VA) status and the efficiency of bioconversion of β‐carotene (BC) to retinol (ROH). Data on plasma ROH kinetics from 2 h to 14 d after an oral tracer dose of [13C10]BC and [13C10]retinyl acetate (RAc) to 33 healthy young adults were analyzed using model‐based compartmental analysis (WinSAAM, the Windows version of the Simulation, Analysis and Modeling software). The 6‐compartment model that fit data for all subjects predicted 5.3 pools of plasma ROH were transferred into extravascular stores each day, with ~17%/d recycling back to plasma; 6.5%/day was irreversibly lost and total body VA stores (TBS) were 146 ± 89 μmol (mean ± SD). We derived a simplified isotope dilution (“Olson”) equation for TBS, eliminating several factors and assumptions: TBS = F * (1 / SA), where F (fraction of dose [FD] absorbed and retained) was estimated as 0.61 from the kinetic data and SA (specific activity) is FD 13C10[ROH] in plasma 3 d after dosing / plasma ROH pool (μmol). TBS calculated using the equation was 149 ± 85 μmol, essentially the same as the value predicted by the model. BC bioconversion, calculated as FD 13C5[ROH] (derived from BC) / 13C10[ROH] (derived from RAc) at 2 d, averaged 23 ± 11% and was significantly correlated (R=0.942) with WinSAAM’s estimate based on areas under the curves (26 ± 12%). Our results indicate that both TBS and BC conversion to ROH can be estimated based on blood samples taken 3 and 2 d, respectively, after dosing. With further refinement, one sample at 3 d may suffice.Grant Funding Source: BBSRC, U.K. and DSM, Basel, Switzerland

Vitamin A-Fortified Milk Increases Total Body Vitamin A Stores in Mexican Preschoolers

Vitamin A (VA) deficiency (VAD) continues to be a major nutritional problem in developing countries, including Central America. In Mexico, milk is a well-accepted vehicle for the administration of micronutrients, including VA, to preschoolers. Thus, we conducted a randomized, controlled, clinical trial to investigate the efficacy of daily consumption of 250 mL of VA-fortified milk (which provided 196 retinol equivalents/d) for 3 mo on VA stores in mildly to moderately VAD (serum retinol concentration 0.35–0.7 μmol/L) preschoolers who were not enrolled in a food assistance program. Twenty-seven mildly to moderately VAD children were randomly assigned based on screening measurements to either the intervention (n = 14) or control group (n = 13) (children in the control group did not receive placebo). All children in the control group and 79% (n = 11) of the children in the intervention group completed the study. The total body VA (TBVA) pool size was estimated using the deuterated retinol dilution technique before and after the intervention. After 3 mo, median changes in the serum retinol concentration for the intervention and control groups were 0.13 and −0.21 μmol/L, respectively (P = 0.009). Median changes in the TBVA stores were 0.06 and 0.01 mmol, respectively (P = 0.006) and estimated median changes in the liver VA concentration were 0.09 and 0.01 μmol/g, respectively (P = 0.002). The VA-fortified milk was well accepted among preschoolers and significantly increased TBVA stores, liver VA stores, and serum retinol concentration, indicating that it may be an effective means to ameliorate VAD in young Mexican children.

Effect of Vitamin A Fortified Milk Intake on Total Body Vitamin A Stores in Mexican Preschoolers

In Mexico, vitamin A deficiency (VAD) is a public health problem for preschool children. Vitamin A (VA) fortified milk (Liconsa) is distributed nationally to fight VAD, nevertheless its effect has yet not been assessed. The aim of this study was to assess the effect of daily intake of VA fortified milk on the total body VA (TBVA) stores of preschoolers.We conducted a randomized controlled clinical trial in Mexico to assess the effect of daily intake of 250 mL of VA fortified Liconsa milk for 12 weeks on VA status of 24 VA‐deficient preschoolers. Subjects were randomly allocated to treatment (n=11) or control (n=13) groups respectively. TBVA stores were calculated using the Olson equation at baseline and three months after daily intake of VA fortified “Liconsa” milk.TBVA stores of the treatment group had a significant increase compared to their baseline value (P&lt;0.05) and stores had a significant difference of 0.75 mmol in treatment vs control groups (P=0.01). Serum retinol concentration was significantly reduced compared to its baseline value in the control group (P&lt;0.05) and serum retinol was 0.291μmol/L greater in the treatment vs control group (P=0.01).Daily intake of vitamin A fortified “Liconsa” milk during 12 weeks, significantly increased TBVA stores and serum retinol levels of Mexican preschoolers.Study supported by the IAEA. LTV received a fellowship from CONACyT.Grant Funding Source : IAEA‐CONACyT

3, 4-Didehydroretinol Kinetics Differ during Lactation in Sows on a Retinol Depletion Regimen and the Serum:Milk 3, 4-Didehydroretinol:Retinol Ratios Are Correlated1–3

3, 4-Didehydroretinol (DR) metabolism was previously followed in vitamin A (VA)-replete lactating sows. This study followed DR appearance and clearance after dosage in serum and milk during 2 lactation cycles in sows (n = 8) fed VA-free feed for 3 gestation-lactation cycles. During lactations 2 and 3, 35 μmol 3, 4-didehydroretinyl acetate was given orally after overnight food deprivation. Blood and milk were collected at 0, 1.5, 3, 5, 7, 9, 16, 24, 36, 48, 60, and 72 h; livers were obtained at kill. Samples were analyzed for DR, retinol (R), and 3, 4-didehydroretinyl esters. During lactations 2 and 3, the 5-h serum DR:R ratios were 0.028 ± 0.017 and 0.069 ± 0.042, respectively, and serum R concentrations were 0.75 ± 0.23 and 0.86 ± 0.37 μmol/L, respectively. The DR:R ratio and serum R were 0.018 ± 0.013 and 0.94 ± 0.12 μmol/L, respectively, in VA-replete sows from the same herd. After lactation 3, liver VA was 0.23 ± 0.05 μmol/g, indicating low-normal VA status. Serum DR area-under-the curve from 0 to 48 h increased as liver stores decreased. Thirteen to 23% of DR dose was secreted into milk, consistent with VA-replete sows. Milk DR concentrations were greater during lactation 3 than 2. Peak concentration occurred earlier and the half-life was shorter for milk DR in the more VA-depleted sows. The milk and serum DR:R were correlated from 3 to 9 h (r = 0.70; P < 0.0001) and increased as VA stores decreased regardless of serum R concentration. Milk DR:R may replace serum measurements during lactation.

Mathematical Modeling of Serum 13C-Retinol in Captive Rhesus Monkeys Provides New Insights on Hypervitaminosis A , ,

Hypervitaminosis A is increasingly a public health concern, and thus noninvasive quantitative methods merit exploration. In this study, we applied the 13C-retinol isotope dilution test to a nonhuman primate model with excessive liver stores. After baseline serum chemistries, rhesus macaques (Macaca mulatta; n = 16) were administered 3.5 μmol 13C2-retinyl acetate. Blood was drawn at baseline, 5 h, and 2, 4, 7, 14, 21, and 28 d following the dose. Liver biopsies were collected 7 d before and 2 d after dosing (n = 4) and at 7, 14, and 28 d (n = 4/time) after dosing. Serum and liver were analyzed by HPLC and GC-combustion-isotope ratio MS for retinol and its enrichment, respectively. Model-based compartmental analysis was applied to serum data. Lactate dehydrogenase was elevated in 50% of the monkeys. Total body reserves (TBR) of vitamin A (VA) were calculated at 28 d. Predicted TBR (3.52 ± 2.01 mmol VA) represented measured liver stores (4.56 ± 1.38 mmol VA; P = 0.124). Predicted liver VA concentrations (13.3 ± 9.7 μmol/g) were similar to measured liver VA concentrations (16.4 ± 5.3 μmol/g). The kinetic models predict that 27–52% of extravascular VA is exchanging with serum in hypervitaminotic A monkeys. The test correctly diagnosed hypervitaminosis A in all monkeys, i.e. 100% sensitivity. Stable isotope techniques have important public health potential for the classification of VA status, including hypervitaminosis, because no other technique besides invasive liver biopsies, correctly identifies excessive liver VA stores.

Assessment of the relative dose-response test based on serum retinol-binding protein instead of serum retinol in determining low hepatic vitamin A stores

Background:The relative dose-response (RDR) test, which measures the percentage of change in serum retinol concentration in response to an oral vitamin A (VA) dose, is a functional reference method to assess low hepatic VA stores. However, problems due to the relative instability of retinol, which is measured in the traditional RDR test, could be circumvented if retinol-binding protein (RBP), a more stable marker of VA, could be measured instead of retinol to provide the RDR value. Objective:The objective was to compare classification of VA status assessed by retinol-RDR with that assessed by using RBP-RDR. Design:With the use of serum samples from 57 lactating women in northern Kenya collected in August-September 2006, we assessed the accuracy of RBP-RDR in predicting low hepatic VA stores through receiver operator characteristic (ROC) analysis using retinol-RDR values as the gold standard. By using regression analysis, we explored the effects of1) body mass index (BMI) on RBP-RDR performance and2) the oral VA dose on the retinol-RBP molar ratio. Results:The classificatory accuracy of RBP-RDR was low to moderate (n = 50; ROC area: 0.56–0.72) depending on the cutoffs used. RBP-RDR systematically overestimated VA deficiency with higher BMI, although it was superior to a single measurement of serum retinol. The discrepancy between RBP-RDR and retinol-RDR appears to originate in a retinol concentration–dependent alteration of the retinol-RBP molar ratio triggered by the oral dose. Conclusions:RBP-RDR has the potential to serve as a moderately accurate surrogate measure of retinol-RDR if the variation associated with BMI is understood and adjusted. Further studies should clarify the dynamics of the retinol-RBP molar ratio and its link to RBP-RDR performance.

Kinetic Analysis Shows that Vitamin A Disposal Rate in Humans Is Positively Correlated with Vitamin A Stores ,

Vitamin A (VA) kinetics, storage, and disposal rate were determined in well-nourished Chinese and U.S. adults using model-based compartmental analysis. [2H8]Retinyl acetate (8.9 μmol) was orally administered to U.S. (n = 12; 59 ± 9 y; mean ± SD) and Chinese adults (n = 14; 54 ± 4 y) and serum tracer and VA concentrations were measured from 3 h to 56 d. Using the Windows version of the Simulation, Analysis and Modeling software, we determined that the average time from dosing until appearance of labeled retinol in serum was greater in U.S. subjects (40.6 ± 8.47 h) than in Chinese subjects (32.2 ± 5.84 h; P < 0.01). Model-predicted total traced mass (898 ± 637 vs. 237 ± 109 μmol), disposal rate (14.7 ± 5.87 vs. 5.58 ± 2.04 μmol/d), and system residence time (58.9 ± 28.7 vs. 42.9 ± 14.6 d) were greater in U.S. than in Chinese subjects (P < 0.05). The model-predicted VA mass and VA mass estimated by deuterated retinol dilution at 3 and 24 d did not differ. VA disposal rate was positively correlated with VA traced mass in Chinese (R2 = 0.556), U.S. (R2 = 0.579), and all subjects (R2 = 0.808). Additionally, VA disposal rate was significantly correlated with serum retinol pool size (R2 = 0.227) and retinol concentration (R2 = 0.330) in all subjects. Our results support the hypothesis that VA stores are the principle determinant of VA disposal rate in healthy, well-nourished adults.

Vitamin A kinetics and utilization in Chinese vs US adults

Vitamin A (VA) kinetics, storage, and utilization were compared in well-nourished Chinese (Wang Z et al., Br J Nutr; 91:–31, 2004) and US adults (Tang G et al., Am J Clin Nutr; 78:–66, 2003). [2H8]Retinyl acetate was orally administered (Chinese: n=15; 55 ± 4 y; mean ± SD and US: n=13; 60 ± 8 y), and plasma tracer and VA concentrations were measured from 3 h to 56 d. Data for plasma tracer vs time were fit to a 7-compartment model using the Simulation, Analysis and Modeling software (WinSAAM). The average time for the appearance of labeled retinol bound to retinol-binding protein in plasma was similar in both groups (~31 h). The plasma retinol pool was 3.34 ± 1.08 in Chinese vs 5.09 ± 1.11 μmol in US subjects (P<0.001); the model-predicted total VA pool was 232 ± 116 and 1866 ± 1603 μmol (P<0.002), and disposal rate was 4.74 ± 2.55 and 9.89 ± 5.15 μmol/d (P<0.0025). Based on these kinetic parameters, Chinese had 54.0 ± 26.9 d of VA stores vs 267 ± 314 d in US adults (P<0.016). Our results indicate that VA stores and disposal rates differ in healthy, well-nourished Chinese and US adults. (Chinese National Natural Science Foundation #30271121 and USDA #51000-065)

Model-based compartmental analysis indicates a reduced mobilization of hepatic vitamin A during inflammation in rats

Vitamin A (VA) kinetics was studied in rats with marginal VA stores before, during, and after inflammation. Rats received orally [11,12-(3)H(N)]retinol ([(3)H]VA; day 0), and inflammation was induced on day 21 with lipopolysacchride (LPS) for 3 days (n = 5) or recombinant human interleukin-6 (rhIL-6) for 7 days (n = 5). Both the fraction of [(3)H]VA and retinol concentrations in plasma were reduced significantly by LPS or rhIL-6. Compartmental analysis using the Windows version of Simulation, Analysis, and Modeling software was applied to group mean data, and non-steady-state models were developed. After absorption, VA kinetics was described by a three-compartment model that included plasma, kidney/interstitium, and liver/carcass. Four mechanisms decreasing plasma retinol were investigated: increased urinary excretion, increased irreversible loss, increased movement into interstitium, and decreased hepatic mobilization. Modeling demonstrated that a 79% reduction in hepatic mobilization of retinol (from 4.3 to 0.9 nmol/h) by 15 h after LPS best accounted for the observed changes in plasma VA kinetics (sum of squares = 9.05 x 10(-07)). rhIL-6 caused an earlier reduction (75% by 5.6 h). These models predicted a return to control values by 10 days after inflammation. If prolonged, inflammation-induced hyporetinolemia can render hepatic retinol unavailable to extrahepatic tissues, possibly leading to their impaired function, as observed in VA-deficient children with measles infection.

Megalin-Mediated Reuptake of Retinol in the Kidneys of Mice Is Essential for Vitamin A Homeostasis

The reuptake of retinol (ROH) and retinol-binding protein (RBP) in the kidneys is mediated by the endocytic receptor megalin, suggesting an important role for this receptor in vitamin A (VA) metabolism. We examined the extent to which megalin deficiency may affect urinary ROH excretion, levels of ROH and RBP in plasma, as well as storage of VA in liver and kidney. For this purpose, mice with a kidney-specific megalin gene defect (megalin(lox/lox); apoE(Cre)) and control mice (megalin(lox/lox)) were fed either a basal diet containing 4500 retinol equivalents (RE)/kg diet or a diet without VA during experimental periods of 42 and 84 d. Urinary ROH excretion was observed only in megalin(lox/lox); apoE(Cre) mice (P < 0.0001, 2-way ANOVA) and not in the controls. Plasma ROH and RBP differed only by diet (P < 0.05), but not genotype (P = 0.615). A major effect of megalin deficiency, however, was evident in retinyl ester levels in the liver (P < 0.05), which were approximately 37% lower than those in megalin(lox/lox) controls (P < 0.05, Student's t test) during the 84-d period of dietary VA deprivation. Kidney levels of VA were not affected by the receptor gene defect. The findings demonstrate that urinary ROH excretion caused by megalin deficiency requires accelerated mobilization of hepatic VA stores to maintain normal plasma ROH levels, which suggests that megalin plays an essential role in systemic VA homeostasis.

Extra-Hepatic Vitamin A Concentrations in Captive Rhesus (Macaca Mulatta) and Marmoset (Callithrix Jacchus) Monkeys Fed Excess Vitamin A

Recent work examining vitamin A (VA) status of rhesus monkeys (Macaca mulatta) used as models for human biomedical research has revealed subtoxic hepatic VA concentrations. Livers of marmoset monkeys (Callithrix jacchus), another experimental animal, were also high in VA as was serum retinyl ester concentration. Both species consumed common research diets that provided up to four times the amount of VA (retinyl acetate) as currently recommended by the National Research Council. To further define the effects of chronically high dietary VA as found in many human subpopulations, we analyzed lung and kidney tissues from subtoxic rhesus and marmoset monkeys (n = 10 each) for retinol and retinyl esters. Marmoset kidneys contained 0.88 +/- 0.66 micromol VA/g and was nearly the same as hepatic VA at 1.40 +/- 0.44 micromol/g (p = 0.143). In contrast, rhesus kidney VA concentrations were 0.0100 +/- 0.0032 micromol/g, even though liver reserves were 18.8 +/- 6.4 micromol VA/g (p < 0.0001). Lung tissue VA concentrations, 0.0022 +/- 0.0012 and 0.0061 +/- 0.0025 micromol/g for marmosets and rhesus, respectively, were lower as compared with kidney (p < 0.011). Kidney and lung VA in monkeys with adequate, but not excessive, VA stores have not been determined; hence, interpretation of these findings is limited to tissue retinol and retinyl ester profiles and extrapolation from other species rather than direct comparison to "normal" values.

Determination of a Cut-Off Value for the Molar Ratio of Retinol-Binding Protein to Transthyretin (RBP:TTR) in Bangladeshi Patients with Low Hepatic Vitamin A Stores

The purpose of this study was to determine a cut-off value of the molar ratio of retinol-binding protein to transthyretin (RBP:TTR) to indicate marginal vitamin A (VA) deficiency. Plasma RBP and TTR were measured by radial immunodiffusion in two groups of patients, i.e., surgical patients with known hepatic VA stores, and a cohort of children residing in a malaria-endemic area of Papua New Guinea who had received placebo or 210 micro mol of VA every 3 mo for 9 mo. A RBP:TTR ratio < or =0.36 selectively detected five of seven patients (71% sensitivity) with hepatic VA stores < or =69.9 nmol/g of tissue (i.e., < or =20 micro g/g), indicative of marginal VA deficiency. Using this cut-off value, 28% (n = 245) of children from Papua New Guinea had marginal VA deficiency before supplementation. After 7 mo, a low ratio persisted in 29% (n = 92) of placebo-treated children but in only 11% (n = 83) of those receiving VA supplements (chi(2), P < 0.01). At the end of the study, 13 mo after initiation or 4 mo after the last dose of VA, the percentage of children with a low ratio was still lower (chi(2), P < 0.02) in the VA group, 42.5% (n = 113) than in the placebo group, 58.6% (n = 118). These results demonstrate that a cut-off value < or =0.36 is indicative of marginal VA deficiency and can be used as an indirect method of VA assessment.

Amount of Dietary Fat and Type of Soluble Fiber Independently Modulate Postabsorptive Conversion of β-Carotene to Vitamin A in Mongolian Gerbils

Current dietary guidelines recommend a decrease in fat intake and an increase in fiber consumption. Decreased bioavailability (BV) of carotenoids is thought to be associated with both of these recommendations. A 2 x 4 factorial design was used to test the effects of dietary fat level at 10 or 30% of total energy and fiber type using no fiber, silica, citrus pectin or oat gum (7 g/100 g) on beta-carotene (betaC) BV in 4- to 5-wk-old Mongolian gerbils. We assessed BV as both accumulation of betaC and bioconversion of betaC to vitamin A (VA) in tissues. A VA- and betaC-deficient diet was fed for 1 wk followed by one of eight isocaloric, semipurified diets supplemented with carrot powder [ approximately 1 microgram betaC, 0.5 microgram alpha-carotene (alphaC)/kJ diet] for 2 wk (n = 12/group). Increasing dietary fat resulted in higher VA (P: = 0.074) and lower betaC (P: = 0.0001) stores in the liver, suggesting that consumption of high fat diets enhances conversion of betaC to VA. The effect of soluble fiber on hepatic VA storage was dependent on fiber type. Consumption of citrus pectin resulted in lower hepatic VA stores and higher hepatic betaC stores compared with all other groups, suggesting less conversion of betaC to VA. In contrast, consumption of oat gum resulted in hepatic VA and betaC stores that were higher (P = 0.012) and lower (P = 0.022), respectively, than those of citrus pectin-fed gerbils. The level of dietary fat consumed with soluble fiber had no interactive effects on hepatic VA, betaC or alphaC stores. Results demonstrate that betaC BV is independently affected by dietary fat level and type of soluble fiber, and suggest that these dietary components modulate postabsorptive conversion of betaC to VA. This study confirms the negative effects of citrus pectin on betaC BV, and suggests that oat gum does not adversely affect betaC BV.

Ferrets (Mustela putoius furo) Inefficiently Convert β-Carotene to Vitamin A 4-5

The ferret has recently been used as a model to evaluate the absorption and metabolism of several carotenoids; however, little is known about the vitamin A (VA) requirements of this species or the ability of ferrets to convert dietary β-carotene (βC) to VA. Three studies were conducted to estimate the daily utilization of VA in ferrets and to determine the effect of prior VA status on the ability of ferrets to utilize βC as a source of VA. Weanling male ferrets were fed a pelleted, low carotenoid, semipurified diet either with (+VA) or without VA (−VA) for 21- to 35-d prefeeding periods. Upon initiation of the experiments, several ferrets were killed to determine base-line VA status. The remaining ferrets were fed VA, βC, or VA and βC in pelleted feed (Studies 1–3) or liquid carrier (Study 3) for 16–21 additional days. Hepatic VA and βC concentrations were used as the primary indicators of VA status, although serum and adrenal VA and βC also were measured. The results showed the following: 1) provision of βC at up to a 15:1 weight ratio of βC to VA in pelleted feed or liquid carrier was not sufficient to maintain hepatic VA stores after a −VA prefeeding period; 2) the daily utilization rate of VA by ferrets ranged from 80 to 171 μg in the three studies; 3) the ferret was confirmed to be a species that has the majority of its serum VA in ester form; and 4) feeding −VA diets significantly reduced serum retinyl esters but had less effect on serum retinol. We conclude that although ferrets can convert βC to VA, the process is inefficient. The ferret model can be most appropriately used when studying the biological effect of tissue βC stores on VA status and is less appropriate for the evaluation of dietary βC conversion to VA.