Mathematical model of zinc absorption: effects of dietary calcium, protein and iron on zinc absorption

Modeling Zinc Absorption in the Adult Population of Colombia: Insights for Nutritional Evaluation and Intervention Strategies

Zinc is a vital trace element, yet its deficiency is common in various populations. This study addresses the gap in understanding zinc intake and its relationship with key nutritional parameters in a Colombian population. We analyzed data from 12,987 individuals, focusing on the daily intake of zinc, phytate, protein, and calcium, and used the phytate/zinc molar ratio as an input parameter in the Miller et al. (2013) model. This model was employed to estimate the total absorbed zinc (TAZ) and the fractional absorption of zinc (FAZ). Our findings highlight a general trend towards insufficient intake compared to the standards of the Institute of Medicine (IOM) and Colombia, with a significant percentage of the population falling below the estimated average requirement (EAR) and recommended daily allowance (RDA) for zinc, underscoring the need for targeted nutritional strategies. Our study contributes to a broader understanding of zinc nutrition and public health implications in Colombia, providing a basis for future dietary guidelines and health interventions.

Dietary Zn deficiency, the current situation and potential solutions

Zinc (Zn) deficiency is a worldwide problem, and this review presents an overview of the magnitude of Zn deficiency with a particular emphasis on present global challenges, current recommendations for Zn intake, and factors that affect dietary requirements. The challenges of monitoring Zn status are clarified together with the discussion of relevant Zn bioaccessibility and bioavailability issues. Modern lifestyle factors that may exacerbate Zn deficiency and new strategies of reducing its effects are presented. Biofortification, as a potentially useful strategy for improving Zn status in sensitive populations, is discussed. The review proposes potential actions that could deliver promising results both in terms of monitoring dietary and physiological Zn status as well as in alleviating dietary Zn deficiency in affected populations.

Plant to animal protein ratio in the diet: nutrient adequacy, long-term health and environmental pressure

Background

Animal and plant protein sources have contrasting relationships with nutrient adequacy and long-term health, and their adequate ratio is highly debated.

Objective

We aimed to explore how the percentage of plant protein in the diet (%PP) relates to nutrient adequacy and long-term health but also to environmental pressures, to determine the adequate and potentially optimal %PP values.

Methods

Observed diets were extracted from the dietary intakes of French adults (INCA3, n = 1,125). Using reference values for nutrients and disease burden risks for foods, we modeled diets with graded %PP values that simultaneously ensure nutrient adequacy, minimize long-term health risks and preserve at best dietary habits. This multi-criteria diet optimization was conducted in a hierarchical manner, giving priority to long-term health over diet proximity, under the constraints of ensuring nutrient adequacy and food cultural acceptability. We explored the tensions between objectives and identified the most critical nutrients and influential constraints by sensitivity analysis. Finally, environmental pressures related to the modeled diets were estimated using the AGRIBALYSE database.

Results

We find that nutrient-adequate diets must fall within the ~15-80% %PP range, a slightly wider range being nevertheless identifiable by waiving the food acceptability constraints. Fully healthy diets, also achieving the minimum-risk exposure levels for both unhealthy and healthy foods, must fall within the 25-70% %PP range. All of these healthy diets were very distant from current typical diet. Those with higher %PP had lower environmental impacts, notably on climate change and land use, while being as far from current diet.

Conclusion

There is no single optimal %PP value when considering only nutrition and health, but high %PP diets are more sustainable. For %PP > 80%, nutrient fortification/supplementation and/or new foods are required.

Higher adherence to the EAT-Lancet reference diet is associated with higher nutrient adequacy in the NutriNet-Santé cohort : a cross-sectional study

BACKGROUND

In 2019, the EAT-Lancet Commission proposed a planetary and healthy reference diet; however, its nutritional quality has been rarely evaluated.

OBJECTIVE

Across different adherence levels to the EAT-Lancet reference diet, the following were our objectives:1) describe the food and nutritional intakes of the French population, 2) to evaluate the nutrient quality and, 3) investigate the consistency between the French national recommendations and the EAT-Lancet reference diet.

DESIGN

This cross-sectional study was conducted among participants of the NutriNet-Santé cohort and the sample was weighted on the characteristics of the general French population. Adherence to the EAT-Lancet reference diet was estimated using the EAT-Lancet Diet Index (ELD-I). Usual nutrient intakes were obtained using the variance reduction method. We used the estimated average requirements cut-point method to estimate the proportion of participants who meet their respective nutritional requirements. Furthermore, the adequacy of the French food-based dietary recommendations (Programme National Nutrition Santé [PNNS]) according to adherence to the EAT-Lancet reference diet was studied.

RESULTS

The weighted sample was composed of 98,465 participants. Except for bioavailable zinc and vitamin B12, we observed a decrease in the nutrient inadequacy prevalence when the adherence to the EAT-Lancet reference diet increased, particularly for vitamin B9 (Q1=37.8% vs. Q5=5.5%, p=<0.0001) and vitamin C (Q1=59.0% vs. Q5=10.8 %, p=<0.0001). However, inadequacy prevalence remained high in all ELD-I quintiles, particularly for fiber (95.9%), vitamin B1 (70.8%), iodine (48.4%), and magnesium (76.8%). Higher ELD-I score was associated with higher adherence for most components of the PNNS, except for food groups that are not specifically included in the EAT-Lancet reference diet and are typical of the French diet, including alcohol, processed meat, and salt.

CONCLUSION

In the French context, although issues with the intake of certain nutrients may occur, a diet that remains within the planetary limits as the EAT-Lancet reference diet allows a favorable nutritional quality.

TRIAL REGISTRATION NUMBER

NCT03335644.

The Molecular Basis for Zinc Bioavailability

Zinc is an essential micronutrient, and its deficiency is perhaps the most prevalent and least understood worldwide. Recent advances have expanded the understanding of zinc’s unique chemistry and molecular roles in a vast array of critical functions. However, beyond the concept of zinc absorption, few studies have explored the molecular basis of zinc bioavailability that determines the proportion of dietary zinc utilized in zinc-dependent processes in the body. The purpose of this review is to merge the concepts of zinc molecular biology and bioavailability with a focus on the molecular determinants of zinc luminal availability, absorption, transport, and utilization.

Nutritionally adequate and environmentally respectful diets are possible for different diet groups: an optimized study from the NutriNet-Santé cohort

BACKGROUND

Research has shown that vegetarian diets have a low environmental impact, but few studies have examined the environmental impacts and nutritional adequacy of these diets together, even though vegetarian diets can lead to nutritional issues.

OBJECTIVES

Our objective was to optimize and compare 6 types of diets with varying degrees of plant foods (lacto-, ovolacto-, and pescovegetarian diets and diets with low, medium, and high meat content) under nutritional constraints.

METHODS

Consumption data in 30,000 participants were derived from the French NutriNet-Santé cohort using an FFQ. Diets were optimized by a nonlinear algorithm minimizing the diet deviation while meeting multiple constraints at both the individual and population levels: nonincrease of the cost and environmental impacts (as partial ReCiPe accounting for greenhouse gas emissions, cumulative energy demand, and land occupation, distinguishing production methods: organic and conventional), under epidemiologic, nutritional (based on nutrient reference values), and acceptability (according to the diet type) constraints.

RESULTS

Optimized diets were successfully identified for each diet type, except that it was impossible to meet the EPA (20:5n-3) + DHA (22:6n-3) requirements in lacto- and ovolactovegetarians. In all cases, meat consumption was redistributed or reduced and the consumption of legumes (including soy-based products), whole grains, and vegetables were increased, whereas some food groups, such as potatoes, fruit juices, and alcoholic beverages, were entirely removed from the diets. The lower environmental impacts (as well as individual indicators) observed for vegetarians could be attained even when nutritional references were reached except for long-chain n-3 (omega-3) fatty acids.

CONCLUSIONS

A low-meat diet could be considered as a target for the general population in the context of sustainable transitions, although all diets tested can be overall nutritionally adequate (except for n-3 fatty acids) when planned appropriately.This trial was registered at clinicaltrials.gov as NCT03335644.

Zinc Fortification: Current Trends and Strategies

Zinc, through its structural and cofactor roles, affects a broad range of critical physiological functions, including growth, metabolism, immune and neurological functions. Zinc deficiency is widespread among populations around the world, and it may, therefore, underlie much of the global burden of malnutrition. Current zinc fortification strategies include biofortification and fortification with zinc salts with a primary focus on staple foods, such as wheat or rice and their products. However, zinc fortification presents unique challenges. Due to the influences of phytate and protein on zinc absorption, successful zinc fortification strategies should consider the impact on zinc bioavailability in the whole diet. When zinc is absorbed with food, shifts in plasma zinc concentrations are minor. However, co-absorbing zinc with food may preferentially direct zinc to cellular compartments where zinc-dependent metabolic processes primarily occur. Although the current lack of sensitive biomarkers of zinc nutritional status reduces the capacity to assess the impact of fortifying foods with zinc, new approaches for assessing zinc utilization are increasing. In this article, we review the tools available for assessing bioavailable zinc, approaches for evaluating the zinc nutritional status of populations consuming zinc fortified foods, and recent trends in fortification strategies to increase zinc absorption.

In-vivo (Albino Mice) and in-vitro Assimilation and Toxicity of Zinc Oxide Nanoparticles in Food Materials

Purpose

Recent advances in nanotechnology have given rise to the potential utilization of nanoparticles as food, nano-medicine/biomedicines.

Patient

The study aimed to investigate the effects of nano-zinc oxide (nano-zinc) on the bio-assimilation of mineral (Zn) in mice, aged 3-6 weeks.

Methods

ZnO nanoparticles were added to the basal diet as a supplement at amounts of 0.07, 0.14 and 0.21 mg/kg. The synthesized material was characterized by Fourier transform infrared spectrophotometer, particle size, scanning electron microscope, Thermogravimetric Analysis Thermal, X-ray diffraction spectrophotometer and Zeta potential.

Results

In-vitro bioavailability of synthesized group ZnO (120 nm) was 43%, whereas for standard group ZnO (50 nm) was reported as 55%. In-vivo bioavailability of zinc oxide illustrated the maximum absorption level compared with the control. In-vivo toxicity was characterized as damage done to the liver and spleen tissues with a high dose of 0.21 mg/kg, while smaller doses indicated no toxic effects.

Conclusion

The study provided important insights on the toxicological effects of ZnO nanoparticles, depending on dose rate and bio-assimilation, as well as particles, under various conditions (in-vitro and in-vivo). These findings will motivate further detailed research on nano-based medicine for alleviating malnutrition conditions.

Modeled healthy eating patterns are largely constrained by currently estimated requirements for bioavailable iron and zinc-a diet optimization study in French adults

BACKGROUND

Healthier dietary patterns involve more plant-based foods than current Western diets rich in animal products containing high amounts of bioavailable iron and zinc. Little consideration is given to the bioavailability of iron and zinc when studying healthy eating patterns.

OBJECTIVES

Our aim was to determine whether currently estimated requirements for bioavailable iron and zinc limit the identification of healthier dietary patterns.

METHODS

Using dietary data from a representative French survey and multicriteria nonlinear optimization, we identified diets that maximize health criteria based on food-based dietary guidelines and concomitantly depart only minimally from the observed diet while complying with all nutrient reference values either strictly (nonflexible optimization) or by allowing bioavailable iron and zinc below the current reference values, but to a limited extent (flexible optimization). Using a comparative risk assessment model, we estimated the resulting impact on cardiometabolic and colorectal cancer mortality/morbidity and changes to iron-deficiency anemia.

RESULTS

Under nonflexible optimization, reference values for bioavailable iron and zinc were the most binding of the 35 nutrient constraints, and modeled diets displayed considerable redistributions within grains and meat. With flexible optimization, modeled diets were healthier as they contained less red meat and more whole-grain products, but would increase iron-deficiency anemia to 5.0% (95% CI: 3.9%, 6.4%). Globally, in terms of disability adjusted life years (DALYs), as the loss due to anemia would represent <30% of the gain otherwise made on chronic diseases, adding flexibility in the iron and zinc reference values would result in a further 18% decrease in the disease burden from 84,768 [95% uncertainty interval (UI): 81,066, 88,470] to 99,689 (95% UI: 95,787, 103,591) DALYs averted.

CONCLUSIONS

Currently estimated requirements for bioavailable iron and zinc proved to be critical factors when modeling healthy eating patterns. Considering lower reference values enables the identification of diets that are apparently healthier overall.

Calcium exacerbates the inhibitory effects of phytic acid on zinc bioavailability in rats

BACKGROUND

Complementary feeding of breastfed infants with foods high in bioavailable zinc (Zn) can help meet physiological requirements for Zn. Some infant cereals contain high concentrations of phytic acid (PA) and calcium (Ca) that may reduce absorbable Zn.

OBJECTIVES

This study measured PA, Zn and Ca concentrations in selected infant cereals sold in Canada and investigated the effects of dietary PA and Ca at concentrations present in infant cereals on Zn bioavailability in rats.

METHODS AND RESULTS

Male Sprague-Dawley rats (36-day old) were fed a control diet containing normal Zn (29.1 mg/kg) and Ca (4.95 g/kg) or six test diets (n = 12/diet group). Test diets were low in Zn (8.91-9.74 mg/kg) and contained low (2.16-2.17 g/kg), normal (5.00-5.11 g/kg) or high (14.6-14.9 g/kg) Ca without or with added PA (8 g/kg). After 2 weeks, rats were killed and Zn status of the rats was assessed. PA, Zn and Ca concentrations in infant cereals (n = 20) differed widely. PA concentrations ranged from undetectable to 16.0 g/kg. Zn and Ca concentrations ranged from 7.0-29.1 mg/kg and 0.8-13.4 g/kg, respectively. The [PA]/[Zn] and [PA × Ca]/[Zn] molar ratios in infants cereals with detectable PA (16 of 20 cereals) ranged from 22-75 and 0.9-14.9 mol/kg, respectively, predicting low Zn bioavailability. Body weight, body composition (lean and fat mass), right femur weight and length measurements and Zn concentrations in serum and femur indicated that diets higher in Ca had a more pronounced negative effect on Zn status of rats fed a PA-supplemented diet. Addition of PA to the diet had a greater negative effect on Zn status when Ca concentration in the diet was higher.

CONCLUSION

These results show that, in rats, higher concentrations of dietary Ca and PA interact to potentiate a decrease in bioavailable Zn and may suggest lower Zn bioavailability in infant cereals with higher PA and Ca concentrations.

Revisiting phytate-element interactions: implications for iron, zinc and calcium bioavailability, with emphasis on legumes

Myo-Inositol hexakisphosphate or phytic acid concentration is a prominent factor known to impede divalent element bioavailability in vegetal foods including legumes. Both in vivo and in vitro studies have suggested that phytic acid and other plant-based constituents may synergistically form insoluble complexes affecting bioavailability of essential elements. This review provides an overview of existing investigations on the role of phytic acid in the binding, solubility and bioavailability of iron, zinc and calcium with a focus on legumes. Given the presence of various interference factors within legume matrices, current findings suggest that the commonly adapted approach of using phytic acid-element molar ratios as a bioavailability predictor may only be valid in limited circumstances. In particular, differences between protein properties and molar concentrations of other interacting ions are likely responsible for the observed poor correlations. The role of phytate degradation in element bioavailability has been previously examined, and in this review we re-emphasize its importance as a tool to enhance mineral bioavailability of mineral fortified legume crops. Food processing strategies to achieve phytate reduction were identified as promising tools to increase mineral bioavailability and included germination and fermentation, particularly when other bioavailability promoters (e.g. NaCl) are simultaneously added.

Revised D-A-CH-reference values for the intake of zinc

BACKGROUND

The Nutrition Societies of Germany, Austria and Switzerland as the joint editors of the 'D-A-CH reference values for nutrient intake' have revised the reference values for zinc in July 2019.

METHODS

For infants aged 0 to under 4 months, an estimated value was set based on the zinc intake via breast feeding. For all other age groups, the reference values were calculated using the factorial method considering endogenous zinc losses via intestinal losses, urine, faeces, skin and sweat, semen in men and the additional zinc requirements to build up body weight in children and adolescents as well as in pregnant women. Due to the strong influence of phytate intake on zinc absorption, the recommendations for the intake of zinc for adults are derived depending on low (0.5 mmol/day, corresponding to 330 mg/day), moderate (1.0 mmol/day, corresponding to 660 mg/day) and high (1.5 mmol/day, corresponding to 990 mg/day) phytate intake. The reference values for lactating women take into account the zinc loss via breast milk.

RESULTS AND CONCLUSION

For adults, pregnant and lactating women, the recommended intake values for zinc range from 7 mg/day to 16 mg/day, depending on sex and dietary phytate intake.

The Effect of Sheep and Cow Milk Supplementation of a Low Calcium Diet on the Distribution of Macro and Trace Minerals in the Organs of Weanling Rats

The aim of this study was to investigate the effect of either sheep or cow milk supplementation to a low calcium and phosphorus diet on growth and organ mineral distribution in weanling rats. Rats were fed diets consisting of either a control chow, a 50% reduced calcium and phosphorous chow (low Ca/P), low Ca/P and sheep milk, or low Ca/P and cow milk diet for 28 days. Food intake of the rats, the growth rate of the rats, and the concentrations of minerals in the soft organs and serum were determined. Rats fed the low Ca/P diet alone had lower weight gain than rats consuming either of the milk-supplemented diets (p < 0.05). Both sheep milk and cow milk supplementation overcame the effects of consuming a diet restricted in calcium and phosphorus but the sheep milk was effective at a significantly lower level of milk intake (p < 0.05). Significant differences (p < 0.05) in essential and trace mineral concentrations due to milk type were observed in the kidney, spleen, and liver. For non-essential minerals, significant differences (p < 0.05), related to diet, were observed in all organs for arsenic, cesium, rubidium, and strontium concentrations.

A short 18 items food frequency questionnaire biochemically validated to estimate zinc status in humans

Inadequate dietary zinc intake is wide-spread in the world's population. Despite the clinical significance of zinc deficiency there is no established method or biomarker to reliably evaluate the zinc status. The aim of our study was to develop a biochemically validated questionnaire as a clinically useful tool that can predict the risk of an individual being zinc deficient. From 71 subjects aged 18-55 years blood and urine samples were collected. Zinc concentrations in serum and urine were determined by atomic absorption spectrometry. A food frequency questionnaire (FFQ) including 38 items was filled out representing the consumption during the last 6 months obtaining nutrient diet scores. Latter were calculated by multiplication of the particular frequency of consumption, the nutrient intake of the respective portion size and the extent of the consumed quantity. Results from the FFQ were compared with nutrient intake information gathered in 24-h dietary recalls. A hemogram was performed and cytokine concentrations were obtained using Enzyme-linked Immunosorbent Assay. Reducing the items of the primary FFQ from 38 to 18 did not result in a significant variance between both calculated scores. Zinc diet scores showed highly significant correlation with serum zinc (r = 0.37; p < 0.01) and urine zinc concentrations (r = 0.34; p < 0.01). Serum zinc concentrations and zinc diet scores showed a significant positive correlation with animal protein intake (r = 0.37; p < 0.01/r = 0.54; p < 0.0001). Higher zinc diet scores were found in omnivores compared to vegetarians (213.5 vs. 111.9; p < 0.0001). The 18 items FFQ seems to be a sufficient tool to provide a good estimation of the zinc status. Moreover, shortening of the questionnaire to 18 items without a loss of predictive efficiency enables a facilitated and resource-saving routine use. A validation of the questionnaire in other cohorts could enable the progression towards clinical utilization of this promising tool.

Approaches used to estimate bioavailability when deriving dietary reference values for iron and zinc in adults

This review aims to describe approaches used to estimate bioavailability when deriving dietary reference values (DRV) for iron and zinc using the factorial approach. Various values have been applied by different expert bodies to convert absorbed iron or zinc into dietary intakes, and these are summarised in this review. The European Food Safety Authority (EFSA) derived zinc requirements from a trivariate saturation response model describing the relationship between zinc absorption and dietary zinc and phytate. The average requirement for men and women was determined as the intercept of the total absorbed zinc needed to meet physiological requirements, calculated according to body weight, with phytate intake levels of 300, 600, 900 and 1200 mg/d, which are representative of mean/median intakes observed in European populations. For iron, the method employed by EFSA was to use whole body iron losses, determined from radioisotope dilution studies, to calculate the quantity of absorbed iron required to maintain null balance. Absorption from the diet was estimated from a probability model based on measures of iron intake and status and physiological requirements for absorbed iron. Average dietary requirements were derived for men and pre- and post-menopausal women. Taking into consideration the complexity of deriving DRV for iron and zinc, mainly due to the limited knowledge on dietary bioavailability, it appears that EFSA has made maximum use of the most relevant up-to-date data to develop novel and transparent DRV for these nutrients.

Drug-development concepts as guides for optimizing clinical trials of supplemental zinc for populations at risk of deficiency or diarrhea

Studies on the efficacy of zinc supplementation for treatment or prevention of diarrhea have shown an inconsistent effect in populations at risk for zinc deficiency. Unlike drugs, which have no preexisting presence in the body, endogenous zinc must be assessed pharmacokinetically by isotope tracer studies. Although such methods have produced much data, very few studies have estimated the dose and the timing of dosing of zinc supplementation. This review examines drug kinetics used to establish the best dose, the timing of such doses, and the mechanism of action through pharmacodynamic markers and applies them, where possible, to zinc supplements. The findings reveal that little is known, especially in children at highest risk of zinc deficiency. Key data missing to inform proper dosing, whether for treatment of disease or for preventive nutrient supplementation, are noted. Addressing these uncertainties could improve study design, leading to future studies of zinc supplements that might be of greater benefit.

Zinc Absorption from Milk Is Affected by Dilution but Not by Thermal Processing, and Milk Enhances Absorption of Zinc from High-Phytate Rice in Young Dutch Women

Background: Milk has been suggested to increase zinc absorption. The effect of processing and the ability of milk to enhance zinc absorption from other foods has not been measured directly in humans.Objective: We aimed to assess zinc absorption from 1) milk undergoing various processing and preparatory steps and 2) from intrinsically labeled high-phytate rice consumed with milk or water.Methods: Two randomized crossover studies were conducted in healthy young women [age:18-25 y; body mass index (in kg/m²): 20-25]: 1) a milk study (n = 19) comparing the consumption of 800 mL full-fat ultra-high temperature (UHT) milk [heat-treated milk (HTM)], full-fat UHT milk diluted 1:1 with water [heat-treated milk and water (MW)], water, or unprocessed (raw) milk (UM), each extrinsically labeled with ⁶⁷Zn, and 2) a rice study (n = 18) comparing the consumption of 90 g intrinsically ⁶⁷Zn-labeled rice with 600 mL of water [rice and water (RW)] or full-fat UHT milk [rice and milk (RM)]. The fractional absorption of zinc (FAZ) was measured with the double-isotope tracer ratio method. In vitro, we assessed zinc extraction from rice blended into water, UM, or HTM with or without phytate.Results: FAZ from HTM was 25.5% (95% CI: 21.6%, 29.4%) and was not different from UM (27.8%; 95% CI: 24.2%, 31.4%). FAZ from water was higher (72.3%; 95% CI: 68.7%, 75.9%), whereas FAZ from MW was lower (19.7%; 95% CI: 17.5%, 21.9%) than HTM and UM (both P < 0.01). FAZ from RM (20.7%; 95% CI: 18.8%, 22.7%) was significantly higher than from RW (12.8%; 95% CI: 10.8%, 14.6%; P < 0.01). In vitro, HTM and UM showed several orders of magnitude higher extraction of zinc from rice with HTM than from rice with water at various phytate concentrations.Conclusions: Milk enhanced human FAZ from high-phytate rice by 62% compared with water. Diluting milk with water decreases its absorption-enhancing proprieties, whereas UHT processing does not. This trial was registered at the Dutch trial registry as NTR4267 (http://www.trialregister.nl/trialreg/admin/rctview.asp?TC=4267).

Effects of Long-Term Exposure to Zinc Oxide Nanoparticles on Development, Zinc Metabolism and Biodistribution of Minerals (Zn, Fe, Cu, Mn) in Mice

Zinc oxide nanoparticles (nano-ZnOs) are widely used and possess great potentials in agriculture and biomedicine. It is inevitable for human exposure to these nanoparticles. However, no study had been conducted to investigate the long term effects of nano-ZnOs. This study aimed at investigating effects of nano-ZnOs on development, zinc metabolism and biodistribution of minerals (Zn, Fe, Cu, and Mn) in mice from week 3 to 35. After the characteristics of nano-ZnOs were determined, they were added into the basal diet at 0, 50, 500 and 5000 mg/kg. Results indicated that added 50 and 500 mg/kg nano-ZnOs showed minimal toxicity. However, 5000 mg/kg nano-ZnOs significantly decreased body weight (from week 4 to 16) and increased the relative weights of the pancreas, brain and lung. Added 5000 mg/kg nano-ZnOs significantly increased the serum glutamic-pyruvic transaminase activity and zinc content, and significantly enhanced mRNA expression of zinc metabolism-related genes, including metallothionein 1(32.66 folds), metallothionein 2 (31.42 folds), ZIP8 (2.21folds), ZIP14 (2.45 folds), ZnT1 (4.76 folds), ZnT2 (6.19 folds) and ZnT4 (1.82 folds). The biodistribution determination showed that there was a significant accumulation of zinc in the liver, pancreas, kidney, and bones (tibia and fibula) after receiving 5000 mg/kg nano-ZnO diet, while no significant effects on Cu, Fe, and Mn levels, except for liver Fe content and pancreas Mn level. Our results demonstrated that long term exposure to 50 and 500 mg/kg nano-ZnO diets showed minimal toxicity. However, high dose of nano-ZnOs (5000 mg/kg) caused toxicity on development, and altered the zinc metabolism and biodistribution in mice.

Fractional Zinc Absorption for Men, Women, and Adolescents Is Overestimated in the Current Dietary Reference Intakes

BACKGROUND

The fractional zinc absorption values used in the current Dietary Reference Intakes (DRIs) for zinc were based on data from published studies. However, the inhibitory effect of phytate was underestimated because of the low phytate content of the diets in the studies used.

OBJECTIVE

The objective of this study was to estimate the fractional absorption of dietary zinc from the US diet by using 2 published algorithms.

METHODS

Nutrient intake data were obtained from the NHANES 2009-2010 and the corresponding Food Patterns Equivalents Database. Data were analyzed with the use of R software by taking into account the complex survey design. The International Zinc Nutrition Consultative Group (IZiNCG; Brown et al. Food Nutr Bull 2004;25:S99-203) and Miller et al. (Br J Nutr 2013;109:695-700) models were used to estimate zinc absorption.

RESULTS

Geometric means (95% CIs) of zinc absorption for all subjects were 30.1% (29.9%, 30.2%) or 31.3% (30.9%, 31.6%) with the use of the IZiNCG model and Miller et al. model, respectively. For men, women, and adolescents, absorption values obtained in this study with the use of the 2 models were 27.2%, 31.4%, and 30.1%, respectively, for the IZiNCG model and 28.0%, 33.0%, and 31.6%, respectively, for the Miller et al. model, compared with the 41%, 48%, and 40%, respectively, used in the current DRIs. For preadolescents, estimated absorption values (31.1% and 32.8% for the IZiNCG model and Miller et al. model, respectively) compare well with the conservative estimate of 30% used in the DRIs. When the new estimates of zinc absorption were applied to the current DRI values for men and women, the results suggest that the Estimated Average Requirement (EAR) and RDA for these groups need to be increased by nearly one-half of the current values in order to meet their requirements for absorbed zinc.

CONCLUSIONS

These data suggest that zinc absorption is overestimated for men, women, and adolescents in the current DRI. Upward adjustments of the DRI for these groups are recommended.

Zinc Absorption Is Not Related to Dietary Phytate Intake in Infants and Young Children Based on Modeling Combined Data from Multiple Studies

BACKGROUND

It is widely understood that the 2 primary factors affecting dietary zinc absorption in adults are the quantities of zinc and phytate in the diet. Although a similar association of absorption to dietary zinc and phytate is presumed to exist in children, to our knowledge, no large-scale examination of the relation of zinc absorption to dietary and growth factors has been conducted.

OBJECTIVE

The goal was to apply an adult absorption model and related models to data from zinc absorption studies of infants and children in order to determine the nature of the relation of zinc absorption to dietary zinc and phytate, age, body size, and zinc homeostatic variables.

METHODS

Data from 236 children between 8 and 50 mo of age were obtained from stable-isotope studies of zinc absorption. Statistical and mechanistic models were fit to the data using linear and nonlinear regression analysis.

RESULTS

The effect of dietary phytate on zinc absorption when controlling for dietary zinc was very small and not statistically discernable (P = 0.29). A 500-mg/d increase in dietary phytate reduced absorbed zinc by <0.04 mg/d. Absorption was observed to vary with age, weight, and height (P < 0.0001) when controlling for dietary zinc. For example, absorption from 6 mg/d of dietary zinc increased by as much as 0.2 mg/d with a 12-mo increase in age. Absorption varied with weight and exchangeable zinc pool size (0.01 < P < 0.05) when controlling for dietary zinc and age.

CONCLUSIONS

The absence of a detectable phytate effect on zinc absorption raises caution about use of dietary phytate:zinc molar ratios to predict zinc bioavailability and does not support phytate reduction as a strategy to improve zinc status of young children. The effect of age on zinc absorption and the absence of a phytate effect should facilitate estimations of dietary zinc needs in young children.

Biomarkers of Nutrition for Development (BOND)-Zinc Review

Zinc is required for multiple metabolic processes as a structural, regulatory, or catalytic ion. Cellular, tissue, and whole-body zinc homeostasis is tightly controlled to sustain metabolic functions over a wide range of zinc intakes, making it difficult to assess zinc insufficiency or excess. The BOND (Biomarkers of Nutrition for Development) Zinc Expert Panel recommends 3 measurements for estimating zinc status: dietary zinc intake, plasma zinc concentration (PZC), and height-for-age of growing infants and children. The amount of dietary zinc potentially available for absorption, which requires an estimate of dietary zinc and phytate, can be used to identify individuals and populations at risk of zinc deficiency. PZCs respond to severe dietary zinc restriction and to zinc supplementation; they also change with shifts in whole-body zinc balance and clinical signs of zinc deficiency. PZC cutoffs are available to identify individuals and populations at risk of zinc deficiency. However, there are limitations in using the PZC to assess zinc status. PZCs respond less to additional zinc provided in food than to a supplement administered between meals, there is considerable interindividual variability in PZCs with changes in dietary zinc, and PZCs are influenced by recent meal consumption, the time of day, inflammation, and certain drugs and hormones. Insufficient data are available on hair, urinary, nail, and blood cell zinc responses to changes in dietary zinc to recommend these biomarkers for assessing zinc status. Of the potential functional indicators of zinc, growth is the only one that is recommended. Because pharmacologic zinc doses are unlikely to enhance growth, a growth response to supplemental zinc is interpreted as indicating pre-existing zinc deficiency. Other functional indicators reviewed but not recommended for assessing zinc nutrition in clinical or field settings because of insufficient information are the activity or amounts of zinc-dependent enzymes and proteins and biomarkers of oxidative stress, inflammation, or DNA damage.

Zinc absorption from biofortified maize meets the requirements of young rural Zambian children

BACKGROUND

The zinc content of maize, a major global food staple, is generally insufficient alone to meet the requirements of young children.

OBJECTIVES

The primary objective of this study was to determine whether substitution of biofortified maize (34 μg zinc/g grain) for control maize (21 μg zinc/g) was adequate to meet zinc physiologic requirements in young children for whom maize was the major food staple. A secondary objective was to compare total daily zinc absorption when maize flour was fortified with zinc oxide to a total concentration of 60 μg zinc/g.

METHODS

Participants included 60 rural Zambian children with a mean age of 29 mo who were randomly assigned to receive 1 of 3 maize types (control, biofortified, or fortified) all of which were readily consumed (>100 g on 1 d). Total daily zinc intake (from maize and low-zinc relish) was determined from duplicate diet collections. Multiplication by fractional absorption of zinc, measured by a dual isotope ratio technique, determined the total daily zinc absorption on the day the test meals were given.

RESULTS

The mean ± SD total daily zinc intake (milligrams per day) from the biofortified maize (5.0 ± 2.2) was higher (P < 0.0001) than for the control maize (2.3 ± 0.9). Intake of zinc from the fortified maize (6.3 ± 2.6) did not differ from the biofortified maize. Fractional absorption of zinc from control maize (0.28 ± 0.10) did not differ from the biofortified maize (0.22 ± 0.06). Total daily absorption of zinc (milligrams per day) from the biofortified maize (1.1 ± 0.5) was higher (P = 0.0001) than for the control maize (0.6 ± 0.2), but did not differ from the fortified maize (1.2 ± 0.4).

CONCLUSIONS

These results indicate that feeding biofortified maize can meet zinc requirements and provide an effective dietary alternative to regular maize for this vulnerable population. This trial was registered at clinicaltrials.gov as NCT02208635.

Zinc absorption from micronutrient powder is low but is not affected by iron in Kenyan infants

Interference with zinc absorption is a proposed explanation for adverse effects of supplemental iron in iron-replete children in malaria endemic settings. We examined the effects of iron in micronutrient powder (MNP) on zinc absorption after three months of home fortification with MNP in maize-based diets in rural Kenyan infants. In a double blind design, six-month-old, non-anemic infants were randomized to MNP containing 5 mg zinc, with or without 12.5 mg of iron (MNP + Fe and MNP − Fe, respectively); a control (C) group received placebo powder. After three months, duplicate diet collections and zinc stable isotopes were used to measure intake from MNP + non-breast milk foods and fractional absorption of zinc (FAZ) by dual isotope ratio method; total absorbed zinc (TAZ, mg/day) was calculated from intake × FAZ. Mean (SEM) TAZ was not different between MNP + Fe (n = 10) and MNP - Fe (n = 9) groups: 0.85 (0.22) and 0.72 (0.19), respectively, but both were higher than C (n = 9): 0.24 (0.03) (p = 0.04). Iron in MNP did not significantly alter zinc absorption, but despite intakes over double estimated dietary requirement, both MNP groups' mean TAZ barely approximated the physiologic requirement for age. Impaired zinc absorption may dictate need for higher zinc doses in vulnerable populations.

Zinc supplementation reduced DNA breaks in Ethiopian women

Assessment of zinc status remains a challenge largely because serum/plasma zinc may not accurately reflect an individual's zinc status. The comet assay, a sensitive method capable of detecting intracellular DNA strand breaks, may serve as a functional biomarker of zinc status. We hypothesized that effects of zinc supplementation on intracellular DNA damage could be assessed from samples collected in field studies in Ethiopia using the comet assay. Forty women, from villages where reported consumption of meat was less than once per month and phytate levels were high, received 20 mg zinc as zinc sulfate or placebo daily for 17 days in a randomized placebo-controlled trial. Plasma zinc concentrations were determined by inductively coupled plasma mass spectrometry. Cells from whole blood at the baseline and end point of the study were embedded in agarose, electrophoresed, and stained before being scored by an investigator blinded to the treatments. Although zinc supplementation did not significantly affect plasma zinc, mean (± SEM) comet tail moment measurement of supplemented women decreased from 39.7 ± 2.7 to 30.0 ± 1.8 (P< .005), indicating a decrease in DNA strand breaks in zinc-supplemented individuals. These findings demonstrated that the comet assay could be used as a functional assay to assess the effects of zinc supplementation on DNA integrity in samples collected in a field setting where food sources of bioavailable zinc are limited. Furthermore, the comet assay was sufficiently sensitive to detect changes in zinc status as a result of supplementation despite no significant changes in plasma zinc.

Bioavailability of iron, zinc, folic acid, and vitamin A from fortified maize

Several strategies appear suitable to improve iron and zinc bioavailability from fortified maize, and fortification per se will increase the intake of bioavailable iron and zinc. Corn masa flour or whole maize should be fortified with sodium iron ethylenediaminetetraacetate (NaFeEDTA), ferrous fumarate, or ferrous sulfate, and degermed corn flour should be fortified with ferrous sulfate or ferrous fumarate. The choice of zinc fortificant appears to have a limited impact on zinc bioavailability. Phytic acid is a major inhibitor of both iron and zinc absorption. Degermination at the mill will reduce phytic acid content, and degermed maize appears to be a suitable vehicle for iron and zinc fortification. Enzymatic phytate degradation may be a suitable home-based technique to enhance the bioavailability of iron and zinc from fortified maize. Bioavailability experiments with low phytic acid-containing maize varieties have suggested an improved zinc bioavailability compared to wild-type counterparts. The bioavailability of folic acid from maize porridge was reported to be slightly higher than from baked wheat bread. The bioavailability of vitamin A provided as encapsulated retinyl esters is generally high and is typically not strongly influenced by the food matrix, but has not been fully investigated in maize.