Zinc absorption and intestinal losses of endogenous zinc in young Chinese women with marginal zinc intakes

Zinc nutrition and dietary zinc supplements

As the second most abundant trace element in the human body, zinc nutrition is constantly a hot topic. More than one-third population is suffering zinc deficiency, which results in various types of diseases or nutritional deficiencies. Traditional ways of zinc supplementation seem with low absorption rates and significant side effects. Zinc supplements with dietary components are easily accessible and improve zinc utilization rate significantly. Also, mechanisms of maintaining zinc homeostasis are of broad interest. The present review focuses on zinc nutrition in human health in inductive methods. Mainly elaborate on different diseases relating to zinc disorder, highlighting the impact on the immune system and the recent COVID-19. Then raise food-derived zinc-binding compounds, including protein, peptide, polysaccharide, and polyphenol, and also analyze their possibilities to serve as zinc complementary. Finally, illustrate the way to maintain zinc homeostasis and the corresponding mechanisms. The review provides data information for maintaining zinc homeostasis with the food-derived matrix.

Zinc Signaling in the Mammary Gland: For Better and for Worse

Zinc (Zn²⁺) plays an essential role in epithelial physiology. Among its many effects, most prominent is its action to accelerate cell proliferation, thereby modulating wound healing. It also mediates affects in the gastrointestinal system, in the testes, and in secretory organs, including the pancreas, salivary, and prostate glands. On the cellular level, Zn²⁺ is involved in protein folding, DNA, and RNA synthesis, and in the function of numerous enzymes. In the mammary gland, Zn²⁺ accumulation in maternal milk is essential for supporting infant growth during the neonatal period. Importantly, Zn²⁺ signaling also has direct roles in controlling mammary gland development or, alternatively, involution. During breast cancer progression, accumulation or redistribution of Zn²⁺ occurs in the mammary gland, with aberrant Zn²⁺ signaling observed in the malignant cells. Here, we review the current understanding of the role of in Zn²⁺ the mammary gland, and the proteins controlling cellular Zn²⁺ homeostasis and signaling, including Zn²⁺ transporters and the Gq-coupled Zn²⁺ sensing receptor, ZnR/GPR39. Significant advances in our understanding of Zn²⁺ signaling in the normal mammary gland as well as in the context of breast cancer provides new avenues for identification of specific targets for breast cancer therapy.

Zinc absorption and zinc status are reduced after either sleeve gastrectomy or Roux-en-Y gastric bypass in premenopausal women with severe obesity studied prospectively over 24 postoperative months

BACKGROUND

Roux-en-Y gastric bypass (RYGBP) is known to reduce zinc absorption; the effects of vertical sleeve gastrectomy (SG) and its long-term implications on zinc absorption have not yet been studied.

OBJECTIVE

The aim was to evaluate the effects of SG and RYGBP on zinc absorption and zinc status in premenopausal women with severe obesity up to 24 mo after surgery.

METHODS

Twenty-six premenopausal women undergoing SG [BMI (in kg/m2): 37.3 ± 3.2] and 32 undergoing RYGBP (BMI: 42.0 ± 4.2) were studied. A series of anthropometric, dietary, and zinc status parameters (plasma and hair zinc), and the size of the exchangeable zinc pool (EZP), as well as percentage zinc absorption from a standardized dose using a stable isotope methodology were evaluated in the patients before the surgical procedure and at 12 and 24 mo after SG or RYGBP. SG patients received 15 mg and RYGBP received 25 mg of supplemental Zn/d.

RESULTS

In premenopausal women, zinc absorption was decreased by 71.9% and 52.0% in SG and RYGBP, respectively, 24 mo postsurgery, compared with initial values. According to 2-factor repeated-measures ANOVA, time effect was significant (P = <0.0001), but not time × group interaction (P = 0.470). Plasma zinc below the cutoff point of 70 µg/dL increased from 0 to 15.4% and 38.1% in SG and RYGBP, respectively. Mean EZP was significantly reduced 24 mo after surgery, although no time × group interactions were observed. Hair zinc did not change across time or between groups.

CONCLUSIONS

Both SG and RYGBP have profound effects on zinc absorption capacity, which are not compensated for after 24 mo. Although zinc absorption reduction was similar in both types of surgeries, plasma zinc was more affected in RYGBP than SG, despite greater zinc supplementation in RYGBP.This trial was registered at http://www.isrctn.com as ISRCTN31937503.

Zinc nutritional status influences ZnT1 and ZIP4 gene expression in children with a high risk of zinc deficiency

INTRODUCTION

Subclinical deficiency of zinc is associated with impairment of immune system function, growth, and cognitive development in children. Although plasma zinc is the best available biomarker of the risk of zinc deficiency in populations, its sensitivity for early detection of deficiency is limited. Therefore, we aimed to investigate zinc deficiency among preschool children and its relationship with whole blood gene expression of zinc transporters ZIP4 and ZnT1.

MATERIAL AND METHODS

This cross-sectional study included 139 children aged 32-76 months enrolled in philanthropic day-care centers. We performed an anthropometric evaluation, weighed food record and dietary record for dietary assessment, blood sample collection for zinc, and whole blood gene expression analyses of ZnT1 (SLC30A1) and ZIP4 (SLC39A4).

RESULTS

Zinc deficiency was observed in 26.6 % of the children despite adequate zinc intake and a phytate:zinc molar ratio < 18. Usual zinc intake did not affect whole blood gene expression of zinc transporters, but zinc status influenced ZnT1 and ZIP4 whole blood mRNA. Children with zinc deficiency exhibited 37.1 % higher ZnT1 expression and 45.3 % lower ZIP4 expression than children with adequate zinc (p < 0.05).

CONCLUSION

Children with plasma zinc deficiency exhibited higher expression of ZnT1 and lower expression of ZIP4 in whole blood mRNA, reinforcing the existence of strong regulation of mineral homeostasis according to the nutritional status, indicating that this analysis may be useful in the evaluation of dietary interventions.

Greater Circulating Copper Concentrations and Copper/Zinc Ratios are Associated with Lower Psychological Distress, But Not Cognitive Performance, in a Sample of Australian Older Adults

Dyshomeostasis of copper and zinc is linked to neurodegeneration. This study investigated the relationship between circulating copper and zinc and copper/zinc ratios and cognitive function, symptoms of depression and anxiety, and neurotrophic factors in older Australian adults. In this cross-sectional study (n = 139), plasma copper, serum zinc, and neurotrophic factors (brain-derived neurotrophic factor (BDNF), vascular endothelial growth factor, and insulin-like growth factor-1) were assessed. Cognition was assessed using the Cogstate battery and the Behavior Rating Inventory (BRI) of Executive Function (Adult version). Symptoms of anxiety and depression were assessed with the Hospital Anxiety and Depression Scale. Copper (β = −0.024; 95% CI = −0.044, −0.004; p = 0.019) and copper/zinc ratio (β = −1.99; 95% CI = −3.41, −0.57; p = 0.006) were associated with lower depressive symptoms, but not cognition. Plasma copper had a modest positive association with BDNF (β = −0.004; 95% CI = 0.000, 0.007; p = 0.021). Zinc was not associated with any of the outcomes. In conclusion, greater circulating copper concentrations and higher copper/zinc ratios were associated with lower depressive symptoms (but not cognition), with copper also positively associated with BDNF concentration, in a sample of community-dwelling older adults.

Maintaining Balance

Writing this biography forced me to look back over my career as a scientist, teacher, wife, and mother. To my surprise, a lifelong theme emerged that I was unaware of, that is, the role of maintaining balance between work and family, science and teaching, mentorship and administration, and personal values and challenges. My primary mentor, Dr. Doris Calloway, demonstrated the importance of maintaining balance. My interest in nutrition started as a preschooler living on a farm where I learned firsthand the importance of balancing the expense of providing good nutrition to the livestock with potential income. In our small high school, I became acquainted with the fascinating field of chemistry, but found it critical to balance that interest with a politically correct field of study for a woman in the early 1960s. I chose dietetics for its strong roots in chemistry. As a US Army dietitian, I learned firsthand how to conduct metabolic studies and knew, immediately, that I had to balance that interest with future opportunities feasible for a dietitian. I chose the University of California, Berkeley, for my PhD because it needed to train dietitians in research to balance an emerging need to offer undergraduates a practicum in dietetics. My subsequent faculty appointment there enabled me to develop novel isotopic approaches for studying zinc and prenatal nutrition, and balance my research with teaching and administrative responsibilities. During the next 40 years, my work as a Berkeley professor led to appointments at the Western Human Nutrition Research Center and Children's Hospital Oakland Research Institute, while balancing my responsibilities as a wife and a mother to my two sons. Balance is defined as a condition in which different elements are equal or in the correct proportions. It is extremely satisfying to look back and see evidence of successfully balancing the disparate elements of my career.

The Linoleic Acid: Dihomo-γ-Linolenic Acid Ratio (LA:DGLA)-An Emerging Biomarker of Zn Status

Zinc (Zn) deficiency is a common aliment predicted to affect 17% of the world's population. Zinc is a vital micronutrient used for over 300 enzymatic reactions and multiple biochemical and structural processes in the body. Although whole blood, plasma, and urine zinc decrease in severe zinc deficiency, accurate assessment of zinc status, especially in mild to moderate deficiency, is difficult as studies with these biomarkers are often contradictory and inconsistent. Hence, as suggested by the World Health Organization, sensitive and specific biological markers of zinc status are still needed. In this review, we provide evidence to demonstrate that the LA:DGLA ratio (linoleic acid:dihomo-γ-linolenic acid ratio) may be a useful additional indicator for assessing Zn status more precisely. However, this biomarker needs to be tested further in order to determine its full potential.

The influence of food consumption and socio-economic factors on the relationship between zinc and iron intake and status in a healthy population

OBJECTIVE

To examine Zn and Fe nutritional status of a healthy population by means of anthropometric, dietary and biochemical measurements and to investigate the relationship of usual Zn and Fe dietary intakes to Zn and Fe status. In addition, to examine the impact of food choices and socio-economic factors on Fe and Zn dietary intakes and status with the aim to identify groups at risk of dietary deficiency and suggest factors that may influence the status of these nutrients.

DESIGN

Food consumption was assessed by 24 h recall questionnaires. Twenty biochemical parameters were measured, of which Hb, haematocrit, erythrocyte count and plasma concentrations of Fe and Zn were directly related to Fe and Zn nutrition. The prevalence of study participants with inadequate micronutrient intakes was calculated using the Estimated Average Requirement cut-point method.

SETTING

Serbia, Europe.

SUBJECTS

Apparently healthy adults (25-65 years of age).

RESULTS

Mean daily Zn and Fe intakes were 9·1 mg and 11·6 mg for males and 7·3 mg and 9·4 mg for females, respectively. Five per cent of the study population had inadequate dietary Fe intake and 15-25 % had inadequate Zn intake. Lower Hb concentrations were measured in women with lower Zn intakes. No differences in Fe and Zn intakes and status among various socio-economic groups were observed, except for Fe intake between the low-income and affluent groups.

CONCLUSIONS

Regular follow-ups are needed to ensure that potential deficiencies of Zn and Fe do get recognized and addressed in a timely manner.

Upregulation of Zinc Absorption Matches Increases in Physiologic Requirements for Zinc in Women Consuming High- or Moderate-Phytate Diets during Late Pregnancy and Early Lactation

Background: Estimated physiologic requirements (PRs) for zinc increase in late pregnancy and early lactation, but the effect on dietary zinc requirements is uncertain.Objective: The aim of this study was to determine changes in daily fractional absorbed zinc and total absorbed zinc (TAZ) from ad libitum diets of differing phytate contents in relation to physiologic zinc requirements during pregnancy and lactation.Methods: This was a prospective observational study of zinc absorption at 8 (phase 1) and 34 (phase 2) wk of gestation and 2 (phase 3) and 6 (phase 4) mo of lactation. Participants were indigenous Guatemalan women of childbearing age whose major food staple was maize and who had been randomly assigned in a larger study to either of 2 ad libitum feeding groups: low-phytate maize (LP; 1.6 mg/g; n = 14) or control maize (C; 7.1 mg/g; n = 8). Total dietary zinc (milligrams per day, TDZ) and phytate (milligrams per day) were determined from duplicate diets and fractional absorption (FAZ) by dual isotope ratio technique (TAZ = TDZ × FAZ). All variables were examined longitudinally and by group and compared with PRs. TAZ values at later phases were compared with phase 1. Measured TAZ was compared with predicted TAZ for nonpregnant, nonlactating (NPNL) women.Results: TAZ was greater in the LP group than in the C group at all phases. All variables increased from phase 1 to phases 2 and 3 and declined at phase 4. TAZ increased by 1.25 mg/d (P = 0.045) in the C group and by 0.81 mg/d (P = 0.058) in the LP group at phase 2. At phase 3, the increases were 2.66 mg/d (P = 0.002) in the C group and 2.28 mg/d (P = 0.0004) in the LP group, compared with a 1.37-mg/d increase in PR. Measured TAZ was greater than predicted values in phases 2-4.Conclusions: Upregulation of zinc absorption in late pregnancy and early lactation matches increases in PRs of pregnant and lactating women, regardless of dietary phytate, which has implications for dietary zinc requirements of pregnant and lactating women.

Predictors of the Size of the Exchangeable Zinc Pool Differ between Children and Adults

BACKGROUND

The size of the rapidly exchanging pool of body zinc has been suggested as having potential utility as a biomarker of zinc status. Knowledge of the relations of exchangeable zinc pool (EZP) size to relevant variables is necessary to adequately evaluate its use as a biomarker.

OBJECTIVE

We used regression analysis to investigate associations of EZP with age, sex, body size, and zinc nutrition variables.

METHODS

Data were compiled from 18 isotope tracer studies of zinc absorption in 247 children and adults (248 observations) in which EZP and relevant variables (e.g., weight, age, absorbed zinc) were measured. Linear regression analyses were performed separately on data from adults and children.

RESULTS

In children, EZP was most strongly associated with weight (r = 0.78). The best-fitting regression models of EZP (R² ≥ 0.68) had weight or age and weight-for-age z score as predictors. Other variables had little effect on EZP when controlling for weight. Absorbed zinc was observed to be a predictor of EZP only in zinc intervention trials of infants. The mean EZP/wt was 4 mg/kg between 8 and 120 mo of age. In adults, EZP was observed to vary in a complex manner with (in order of importance) age, absorbed zinc, weight, sex, and plasma zinc concentration. EZP data from zinc-deprived subjects were lower than the 95% prediction interval of a model of normative data.

CONCLUSIONS

EZP was observed to maintain a constant size relative to weight and was influenced only slightly by other factors in children. In contrast, EZP in adults varied with several factors, including absorbed zinc, and was statistically smaller in zinc-deprived individuals. The findings suggest that EZP may have utility as an indicator of zinc status in adults, but there is less evidence for this in children. Additional data are needed to reach a definitive conclusion.

Photodynamic Therapy Mediated by Nontoxic Core-Shell Nanoparticles Synergizes with Immune Checkpoint Blockade To Elicit Antitumor Immunity and Antimetastatic Effect on Breast Cancer

An effective, nontoxic, tumor-specific immunotherapy is the ultimate goal in the battle against cancer, especially the metastatic disease. Checkpoint blockade-based immunotherapies have been shown to be extraordinarily effective but benefit only the minority of patients whose tumors have been pre-infiltrated by T cells. Here, we show that Zn-pyrophosphate (ZnP) nanoparticles loaded with the photosensitizer pyrolipid (ZnP@pyro) can kill tumor cells upon irradiation with light directly by inducing apoptosis and/or necrosis and indirectly by disrupting tumor vasculature and increasing tumor immunogenicity. Furthermore, immunogenic ZnP@pyro photodynamic therapy (PDT) treatment sensitizes tumors to checkpoint inhibition mediated by a PD-L1 antibody, not only eradicating the primary 4T1 breast tumor but also significantly preventing metastasis to the lung. The abscopal effects on both 4T1 and TUBO bilateral syngeneic mouse models further demonstrate that ZnP@pyro PDT treatment combined with anti-PD-L1 results in the eradication of light-irradiated primary tumors and the complete inhibition of untreated distant tumors by generating a systemic tumor-specific cytotoxic T cell response. These findings indicate that nanoparticle-mediated PDT can potentiate the systemic efficacy of checkpoint blockade immunotherapies by activating the innate and adaptive immune systems in tumor microenvironment.

Use of Serum Zinc Concentration as an Indicator of Population Zinc Status

Assessing the prevalence and severity of zinc deficiency in populations is critical to determine the need for and appropriate targeting of zinc intervention programs and to assess their effectiveness for improving the health and well-being of high-risk populations. However, there is very little information on the zinc status of populations worldwide due to the lack of consensus on appropriate biochemical indicators of zinc status. The objective of this review was to evaluate the use of serum zinc concentration as an indicator of population zinc status.

We have reviewed the response of serum zinc concentration to dietary zinc restriction and zinc supplementation. In addition, we completed pooled analyses of nine zinc intervention trials in young children to assess the relations between serum zinc concentration of individuals before treatment and their responses to zinc supplementation. Also, in updated combined analyses of previously published data, we investigated the relation between the mean initial serum zinc concentration of a study population and their mean growth responses to zinc supplementation in randomized intervention trials among children.

The results from depletion/repletion studies indicate that serum zinc concentrations respond appreciably to severe dietary zinc restriction, although there is considerable interindividual variation in these responses. There is also clear evidence that both individual and population mean serum zinc concentrations increase consistently during zinc supplementation, regardless of the initial level of serum zinc concentration. By contrast, an individual's serum zinc concentration does not reliably predict that person's response to zinc supplementation.

Serum zinc concentration can be considered a useful biomarker of a population's risk of zinc deficiency and response to zinc interventions, although it may not be a reliable indicator of individual zinc status.

Stable Isotopes of Minerals as Metabolic Tracers in Human Nutrition Research

Enriched stable isotopes used as tracers have proven to be valuable in studies of the absorption and metabolism of minerals. Unlike radioisotopes, they can be used in high-risk population groups such as infants, children, and pregnant or lactating women. Estimates of mineral absorption can be made from the oral administration of a single tracer or from two tracers, one given orally and the other intravenously (IV). It is possible to determine the metabolism of the mineral with modeling based on the amount of the tracer or tracers in different biological samples. One of the key decisions in studies of this type is determining which enriched isotope and what amount to use. An example is given of calculations to estimate and compare the amounts of tracers needed for an absorption study. Methods for calculating the amounts of tracer in oral and IV doses are presented, and limits of detection and quantitation are discussed in terms of percent of enrichment and related to isotope ratio measurement precision. A general review of the use of mass spectrometric instruments for quantifying various stable isotopes is given.

An initial evaluation of newly proposed biomarker of zinc status in humans - linoleic acid: dihomo-γ-linolenic acid (LA:DGLA) ratio

BACKGROUND

Zinc is an essential micronutrient for humans with important physiological functions. A sensitive and specific biomarker for assessing Zn status is still needed.

OBJECTIVE

The major aim of this study was to examine if the changes in the content of plasma phospholipid LA, DGLA and LA: DGLA ratio can be used to efficiently predict the dietary Zn intake and plasma Zn status of humans.

METHODS

The study was performed on healthy human volunteers, 25-55 years of age. The dietary Zn intake was assessed using 24 h recall questionnaires. Plasma phospholipid fatty acid analysis was done by gas chromatography, and plasma analysis of minerals by atomic absorption spectrometry. Biochemical, anthropometrical and hematological parameters were assessed.

RESULTS

No significant relationship was found between the dietary and plasma zinc status (r = 0.07; p = 0.6). There was a statistically significant correlation between DGLA and plasma Zn (r = 0.39, p = 0.00). No relationship was observed between the linoleic acid and plasma Zn, while there was a significant negative correlation between LA: DGLA ratio and plasma Zn status (r = -0.35, p = 0.01). Similarly, there were statistically significant difference in DGLA status (p = 0.004) and LA: DGLA ratio (p = 0.042) between the Zn formed groups.

CONCLUSIONS

This study is an initial step in evaluating LA: DGLA ratio as a biomarker of Zn status in humans. The results are encouraging as they show that concentration of DGLA is decreased and LA: DGLA ratio increased in people with lower dietary Zn intake. However, additional studies are needed to fully examine the sensitivity of this biomarker.

The effect of parity on maternal body mass index, plasma mineral element status and new-born anthropometrics

BACKGROUND

Adverse pregnancy outcome is an important public health problem that has been partly associated with increasing maternal parity.

AIM

To determine the effect of parity on maternal body mass index (BMI), mineral element status and newborn anthropometrics.

METHODS

Data for 349 pregnant women previously studied for the impacts of maternal plasma mineral element status on pregnancy and its outcomes was analysed. Obstetric and demographic data and 5mls of blood samples were obtained from each subject. Blood lead, plasma copper, iron and zinc were determined using atomic absorption spectrophotometer.

RESULTS

Maternal BMI increases with parity. Women with parity two had significantly higher plasma zinc but lower plasma copper with comparable levels of the elements in nulliparous and higher parity groups. Although plasma iron was comparable among the groups, blood lead was significantly higher in parity > three. Newborn birth length increases with parity with a positive correlation between parity and maternal BMI (r = 0.221; p = 0.001) and newborn birth length (r = 0.170; p = 0.002) while plasma copper was negatively correlated with newborn's head circumference (r = -0.115; p = 0.040).

CONCLUSION

It is plausible that parity affects maternal BMI and newborn anthropometrics through alterations in maternal plasma mineral element levels. While further studies are desired to confirm the present findings, there is need for pregnant and would-be pregnant women to diversify their diet to optimize their mineral element status.

The potential for zinc stable isotope techniques and modelling to determine optimal zinc supplementation

It is well recognised that zinc deficiency is a major global public health issue, particularly in young children in low-income countries with diarrhoea and environmental enteropathy. Zinc supplementation is regarded as a powerful tool to correct zinc deficiency as well as to treat a variety of physiologic and pathologic conditions. However, the dose and frequency of its use as well as the choice of zinc salt are not clearly defined regardless of whether it is used to treat a disease or correct a nutritional deficiency. We discuss the application of zinc stable isotope tracer techniques to assess zinc physiology, metabolism and homeostasis and how these can address knowledge gaps in zinc supplementation pharmacokinetics. This may help to resolve optimal dose, frequency, length of administration, timing of delivery to food intake and choice of zinc compound. It appears that long-term preventive supplementation can be administered much less frequently than daily but more research needs to be undertaken to better understand how best to intervene with zinc in children at risk of zinc deficiency. Stable isotope techniques, linked with saturation response and compartmental modelling, also have the potential to assist in the continued search for simple markers of zinc status in health, malnutrition and disease.

Resistant starch does not affect zinc homeostasis in rural Malawian children

OBJECTIVE

This study tested the hypothesis that Malawian children at risk for zinc deficiency will have reduced endogenous fecal zinc (EFZ) and increased net absorbed zinc (NAZ) following the addition of high amylose maize resistant starch (RS) to their diet.

METHODS

This was a small controlled clinical trial to determine the effects of added dietary RS on zinc homeostasis among 17 stunted children, aged 3-5 years consuming a plant-based diet and at risk for perturbed zinc homeostasis. Dual zinc stable isotope studies were performed before and after 28 d of intervention with RS, so that each child served as their own control. The RS was incorporated into fried wheat flour dough and given under direct observation twice daily for 28 d. Changes in zinc homeostatic measures were compared using paired Student's t-tests and linear regression analysis.

RESULTS

Children had a mean height-for-age Z-score of -3.3, and consumed animal source foods ≤twice per month. Their habitual diet contained a phytate:zinc molar ratio of 34:1. Children avidly consumed the RS without complaints. EFZ was 0.8±0.4mg/d (mean±SD) both before and after the intervention. Fractional absorption of zinc was 0.38±0.08 and 0.35±0.06 before and after the RS intervention respectively. NAZ was 1.1±0.5 and 0.6±0.7 before and after the RS intervention. This reduction of NAZ corresponded with diminished dietary zinc intake on the study day following intervention with RS. Regression analysis indicated no change in zinc absorption relative to dietary intake as a result of the RS intervention.

CONCLUSION

Consumption of RS did not improve zinc homeostasis in rural African children without zinc deficiency. RS was well tolerated in this setting.

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.

Vegetarian diets across the lifecycle: impact on zinc intake and status

Optimal zinc status is an important consideration when evaluating the nutritional adequacy of vegetarian diets. In the absence of animal tissue sources of zinc and with increased intake of inhibitors of zinc absorption, phytic acid in particular, the bioavailability of zinc is thought to be lower from vegetarian as compared to omnivorous diets. The aim of this chapter is to review the research that examines the effects of vegetarian compared to omnivorous diets on zinc intake and zinc status in the elderly, adults, children, pregnancy, and lactation. A narrative review of the published literature was undertaken, focusing on observational studies in humans that reported zinc intake and biomarkers of zinc status at various stages of the life cycle. Compared to their respective nonvegetarian control groups, adult male and female vegetarians have lower dietary zinc intakes and serum zinc concentrations. However in the elderly, children, and in women during pregnancy and lactation, there is insufficient evidence to determine whether zinc intake and status are lower in vegetarians compared to omnivores. Inconsistencies in study findings reflect variations inherent in the definition of vegetarian diets, and in many instances compromised statistical power due to a small sample size. Improved methods for the assessment of zinc status are required to determine whether homeostatic responses are sufficient to maintain an adequate zinc status in vegetarians, particularly during times of increased requirement. Appropriate dietary advice to increase the zinc content and bioavailability of vegetarian diets throughout the life cycle is prudent.

Zinc deficiency in infants and children: a review of its complex and synergistic interactions

Zinc deficiency is estimated to contribute to over half a million deaths per year in infants and children under 5 years of age. This paper reviews the features of mild-to-moderate zinc deficiency, which include growth faltering, deficits in immune function and altered integrity and function of the gastro-intestinal tract. Sub-clinical features include oxidative stress and a pro-inflammatory state. The homeostatic response to low dietary zinc intake by increasing absorption is limited, especially if the source of zinc is of poor bioavailability, and conservation of endogenous intestinal losses is a critical component of adaptation. Owing to low zinc intakes, older breastfed infants, especially those of low birthweight, are predictably at risk of zinc deficiency if complementary food choices are unfortified and/or low in zinc. Host factors such as young age, poor intra-uterine zinc accretion owing to poor maternal status and/or prematurity, and gastro-intestinal dysfunction also potently predispose to zinc deficiency. Environmental enteropathy, which is prevalent in low-resource settings, may substantially impair zinc absorption and/or increase endogenous losses, and thus lead to relatively high zinc requirements. Emerging evidence highlights common features between chronic inflammation and zinc deficiency, and each may exacerbate the other. More investigations of zinc homeostasis in populations in low-resource settings are needed to better quantify absorption capacity and losses. Effective preventive strategies must address potentially higher zinc requirements as well as the underlying context that perpetuates a vicious cycle of zinc deficiency and multiple adverse outcomes.

Zinc deficiency in children with environmental enteropathy-development of new strategies: report from an expert workshop

Zinc deficiency is a major cause of childhood morbidity and mortality. The WHO/UNICEF strategy for zinc supplementation as adjunctive therapy for diarrhea is poorly implemented. A conference of experts in zinc nutrition and gastrointestinal disorders was convened to consider approaches that might complement the current recommendation and what research was needed to develop these approaches. Several key points were identified. The design of novel zinc interventions would be facilitated by a better understanding of how disturbed gut function, such as environmental (or tropical) enteropathy, affects zinc absorption, losses, and homeostasis. Because only 10% of zinc stores are able to be rapidly turned over, and appear to be rapidly depleted by acute intestinal illness, they are probably best maintained by complementary regular supplementation in a primary prevention strategy rather than secondary prevention triggered by acute diarrhea. The assessment of zinc status is challenging and complex without simple, validated measures to facilitate field testing of novel interventions. Zinc bioavailability may be a crucial factor in the success of primary prevention strategies, and a range of options, all still inadequately explored, might be valuable in improving zinc nutrition. Some therapeutic actions of zinc on diarrhea seem attributable to pharmacologic effects, whereas others are related to the reversal of deficiency (ie, nutritional). The distinction between these 2 mechanisms cannot be clarified given the insensitivity of serum zinc to identify subclinical deficiency states. Why zinc seems to be less effective than expected at all ages, and ineffective for secondary prevention of diarrhea in children <12 mo of age, remains unclear. It was concluded that a reframing of the current recommendation is warranted with consideration of how to better optimize and deliver zinc and whether to provide a complementary public health primary prevention zinc strategy. This requires careful consideration of the zinc product to be used as well as strategies for its delivery.

Comparison of the nutritional status and outcome in thermal burn patients receiving vegetarian and non-vegetarian diets

BACKGROUND

The importance of adequate nutritional support in burned patients cannot be overemphasised. For adequate long-term compliance by the patients, diet should be formulated in accordance with their pre-burn dietary habits, religious beliefs, and tastes.

PATIENTS AND METHODS

A study was conducted in 42 consecutive patients suffering from 10% to 50% of 2(nd) and 3(rd) degree thermal burns with the aim to compare nutritional status, clinical outcome, and cost-effectiveness of vegetarian and non-vegetarian diets. The patients were divided into two groups depending upon their pre-injury food habits. Total calories were calculated by Curreri formula. Both groups were compared by various biochemical parameters, microbiological investigations, weight, status of wound healing, graft take, and hospital stay and they were followed for at least 60 days postburn.

RESULTS

The results were comparable in both groups. Vegetarian diet was found to be more palatable and cost-effective.

CONCLUSION

Vegetarian diet is a safe and viable option for the patients suffering from burn injury. The common belief that non-vegetarian diet is superior to vegetarian diet is a myth.

Interactions between zinc deficiency and environmental enteropathy in developing countries

Zinc deficiency affects one-fifth of the world's population and leads to substantial morbidity and mortality. Environmental enteropathy (EE), a subclinical pathology of altered intestinal morphology and function, is almost universal among people living in developing countries and affects long-term growth and health. This review explores the overlapping nature of these 2 conditions and presents evidence for their interaction. EE leads to impaired zinc homeostasis, predominantly due to reduced absorptive capacity arising from disturbed intestinal architecture, and zinc deficiency exacerbates several of the proposed pathways that underlie EE, including intestinal permeability, enteric infection, and chronic inflammation. Ongoing zinc deficiency likely perpetuates the adverse outcomes of EE by worsening malabsorption, reducing intestinal mucosal immune responses, and exacerbating systemic inflammation. Although the etiology of EE is predominantly environmental, zinc deficiency may also have a role in its pathogenesis. Given the impact of both EE and zinc deficiency on morbidity and mortality in developing countries, better understanding the relation between these 2 conditions may be critical for developing combined interventions to improve child health.

Iron and zinc nutrition in the economically-developed world: a review

This review compares iron and zinc food sources, dietary intakes, dietary recommendations, nutritional status, bioavailability and interactions, with a focus on adults in economically-developed countries. The main sources of iron and zinc are cereals and meat, with fortificant iron and zinc potentially making an important contribution. Current fortification practices are concerning as there is little regulation or monitoring of intakes. In the countries included in this review, the proportion of individuals with iron intakes below recommendations was similar to the proportion of individuals with suboptimal iron status. Due to a lack of population zinc status information, similar comparisons cannot be made for zinc intakes and status. Significant data indicate that inhibitors of iron absorption include phytate, polyphenols, soy protein and calcium, and enhancers include animal tissue and ascorbic acid. It appears that of these, only phytate and soy protein also inhibit zinc absorption. Most data are derived from single-meal studies, which tend to amplify impacts on iron absorption in contrast to studies that utilize a realistic food matrix. These interactions need to be substantiated by studies that account for whole diets, however in the interim, it may be prudent for those at risk of iron deficiency to maximize absorption by reducing consumption of inhibitors and including enhancers at mealtimes.

Inclusion of guava enhances non-heme iron bioavailability but not fractional zinc absorption from a rice-based meal in adolescents

Assessing the bioavailability of non-heme iron and zinc is essential for recommending diets that meet the increased growth-related demand for these nutrients. We studied the bioavailability of iron and zinc from a rice-based meal in 16 adolescent boys and girls, 13-15 y of age, from 2 government-run residential schools. Participants were given a standardized rice meal (regular) and the same meal with 100 g of guava fruit (modified) with (57)Fe on 2 consecutive days. A single oral dose of (58)Fe in orange juice was given at a separate time as a reference dose. Zinc absorption was assessed by using (70)Zn, administered intravenously, and (67)Zn given orally with meals. The mean hemoglobin concentration was similar in girls (129 ± 7.8 g/L) and boys (126 ± 7.1 g/L). There were no sex differences in the indicators of iron and zinc status except for a higher hepcidin concentration in boys (P < 0.05). The regular and modified meals were similar in total iron (10-13 mg/meal) and zinc (2.7 mg/meal) content. The molar ratio of iron to phytic acid was >1:1, but the modified diet had 20 times greater ascorbic acid content. The absorption of (57)Fe from the modified meal, compared with regular meal, was significantly (P < 0.05) greater in both girls (23.9 ± 11.2 vs. 9.7 ± 6.5%) and boys (19.2 ± 8.4 vs. 8.6 ± 4.1%). Fractional zinc absorption was similar between the regular and modified meals in both sexes. Hepcidin was found to be a significant predictor of iron absorption (standardized β = -0.63, P = 0.001, R(2) = 0.40) from the reference dose. There was no significant effect of sex on iron and zinc bioavailability from meals. We conclude that simultaneous ingestion of guava fruit with a habitual rice-based meal enhances iron bioavailability in adolescents.

Use of stable isotopes and mathematical modelling to investigate human mineral metabolism

Individuals have varying needs for minerals that are dependent, amongst other things, on their lifestyle, age and genetic makeup. Knowledge of exact individual nutritional requirements should lead to better health, increased quality of life and reduced need for expensive medical care. Bioavailability, nutrient-gene interactions and whole-body metabolism all need to be investigated further if we are to progress towards the goal of defining optimal health and nutritional status. The discussion which follows will critically review the latest developments in the area of metabolism for several of the minerals that are essential for human health: Ca, Zn, Cu and Se. Stable-isotope tracers and mathematical modelling are some of the tools being used to facilitate the greater understanding in uptake, utilisation and excretion of these minerals. Stable isotopes, administered in physiological doses, present little or no risk to volunteers and allow metabolic studies to be carried out in vulnerable population groups such as children and pregnant women. Intrinsic labelling of foodstuffs ensures that the tracer and the native mineral will behave similarly once inside the body. Advances in computing power and software dedicated to solving nutritional problems have made it possible for investigators to use mathematical modelling in their experimental work. Mineral metabolism is ideally suited to a form of modelling known as compartmental analysis, which allows rates of mineral transferand sizes of mineral stores to be calculated accurately without the need for invasive sampling of body tissues.

Zinc absorption and zinc status are reduced after Roux-en-Y gastric bypass: a randomized study using 2 supplements

BACKGROUND

Micronutrient deficiencies are common in patients undergoing gastric bypass. The effect of this type of surgery on zinc absorption and zinc status is not well known.

OBJECTIVE

The objective was to evaluate the effects of Roux-en-Y gastric bypass (RYGBP) on zinc status and zinc absorption at different stages after surgery. We hypothesized that zinc status would be significantly impaired after surgery and that this impairment would be less severe in subjects receiving increased supplemental zinc. We also hypothesized that zinc absorption would be lower after surgery.

DESIGN

Anthropometric and body-composition variables and dietary and biochemical indexes of zinc status and zinc absorption were determined in 67 severe and morbidly obese women [mean (±SD) age: 36.9 ± 9.8 y; BMI (in kg/m(2)): 45.2 ± 4.7] who underwent RYGBP. The subjects were randomly assigned to 1 of 2 vitamin-mineral supplementation groups. Measurements were made before and 6, 12, and 18 mo after surgery. Fifty-six subjects completed the 18-mo follow-up.

RESULTS

Mean plasma zinc, erythrocyte membrane alkaline phosphatase activity, and the size of the rapidly exchangeable zinc pool decreased after RYGBP. Percentage zinc absorption decreased significantly from 32.3% to 13.6% at 6 mo after RYGBP and to 21% at 18 mo after surgery. No effect of supplement type was observed.

CONCLUSIONS

Zinc status is impaired after RYGBP, despite the finding that dietary plus supplemental zinc doubled recommended zinc intakes in healthy persons. Zinc absorption capacity is significantly reduced soon after RYGBP, with no major changes until 18 mo after surgery.

Zinc homeostasis and gut function in children with celiac disease

BACKGROUND

Celiac disease (CD) is an immunologic enteropathy triggered by the intake of gluten. It is thought that the enteropathy impairs gut function and absorption.

OBJECTIVE

We assessed the zinc-absorption capacity and small-bowel integrity in children with CD.

DESIGN

Children in whom a diagnosis of CD was considered clinically and either confirmed (n = 16; Marsh score ≥3) or not (n = 22; Marsh score of 0) with a small-bowel biopsy (SBB) were recruited. The fractional absorption of zinc (FAZ) was determined by the administration of an oral (67)Zn dose (2.5 mg) and an intravenous (70)Zn dose (0.2 mg) 2 h before and during the SBB, respectively. Spot urine samples were collected, and zinc isotopic ratios were determined by ion-coupled plasma mass spectrometry. Gut health was assessed by the ingestion of (13)C-sucrose (20 g) after an overnight fast, and breath samples were collected and analyzed by isotope ratio mass spectrometry.

RESULTS

There was no difference in FAZ between children with a Marsh score ≥3 (mean ± SEM: 0.68 ± 0.05) and children with a Marsh score of 0 (0.74 ± 0.05). The exchangeable zinc pool (EZP) was significantly (P < 0.05) lower in children with a Marsh score ≥3 (2.6 ± 0.8 mg/kg) than in children with a Marsh score of 0 (3.8 ± 1.4 mg/kg). Gut function in children with a Marsh score ≥3 (4.5 ± 0.7% cumulative dose recovered at 90 min) was lower than the lower cutoff of a normal gut-function breath test (5.06% cumulative dose recovered at 90 min) but not significantly different from that in children with a Marsh score of 0 (4.9 ± 0.4%). There was a significant (P < 0.01) correlation between zinc absorption and gut function in children with CD.

CONCLUSIONS

Zinc absorption did not appear below usual amounts in subjects with CD. Children with CD have impaired gut function that may affect their zinc nutritional status as shown by a smaller EZP. However, the EZP decrease in children with CD was not compared with that in healthy control subjects, and its biological meaning is uncertain.

Physiological requirements for zinc

The estimates of zinc physiological requirements by the International Zinc Nutrition Consultative Group (IZiNCG) in 2004 were conspicuously low in comparison with those estimated by the Institute of Medicine (IOM) in 2001. The objective of this review is to explore the reasons for this gap and to reflect on lessons learned. All estimates of inevitable losses of endogenous zinc, especially intestinal excretion of endogenous zinc, were reviewed. An error in zinc menstrual losses, as well as a minor error in the linear regression of endogenous fecal zinc (EFZ) vs. total daily zinc absorption (TAZ) by IOM, were corrected. The review revealed an error by IZiNCG in selecting two data points for the linear regression of EFZ on TAZ. A second major reason for the "gap" is attributable to weighting of the data in the regression analysis by number of subjects per study by IZiNCG. Adjusting for these factors, together with use of the same reference data for body weights, resulted in satisfactory agreement between the two estimates of physiological requirements. The lessons to be learned from this review are discussed together with suggestions for future action by IOM as well as a constructive role for IZiNCG.

Perturbed zinc homeostasis in rural 3-5-y-old Malawian children is associated with abnormalities in intestinal permeability attributed to tropical enteropathy

Tropical enteropathy and zinc deficiency are major public health problems worldwide. Tropical enteropathy is characterized by reduced mannitol absorption with normal or increased lactulose absorption when a dual sugar absorption test is administered, the results of which are reported as the lactulose:mannitol ratio (L:M). Zinc homeostasis is quantified with a dual stable isotope test. This study tested the hypothesis that endogenous fecal zinc (EFZ) was correlated with the L:M. A dual sugar absorption test and dual stable isotope test were performed on 25 asymptomatic Malawian children aged 3-5 y at risk for tropical enteropathy and zinc deficiency. EFZ and net zinc retention were estimated and correlated with the L:M. Twenty-two children (88%) had an abnormal L:M (L:M>0.10), and the L:M was 0.24+/-0.10 (mean+/-SD). EFZ was 1.68+/-1.06 mg/d, a quantity greater than is seen in healthy populations from the developed world. EFZ was positively correlated with the L:M (r=0.62, p<0.001). Net zinc retention (0.67+/-1.6 mg/d) was negatively correlated with the L:M (r=-0.47, p=0.02). This suggests that perturbed zinc homeostasis is associated with subclinical enteropathy in these children.

Zinc bioavailability and homeostasis

Zinc has earned recognition recently as a micronutrient of outstanding and diverse biological, clinical, and global public health importance. Regulation of absorption by zinc transporters in the enterocyte, together with saturation kinetics of the absorption process into and across the enterocyte, are the principal means by which whole-body zinc homeostasis is maintained. Several physiologic factors, most notably the quantity of zinc ingested, determine the quantity of zinc absorbed and the efficiency of absorption. Other factors are age and the time over which zinc is ingested. Zinc from supplements has not been shown to be absorbed differently from that taken with meals that lack inhibitors of zinc absorption. The principal dietary factor known to impair zinc bioavailability is inositol hexa- (and penta-) phosphate or phytate. Modeling of zinc absorption as a function of dietary zinc and phytate accounts for >80% of the variability in the quantity of zinc absorbed. Fitting the model to new data has resulted in continual improvement in parameter estimates, which currently indicate a maximal absorption in adults of approximately 6 mg Zn/d and that the average estimated dietary requirement doubles with 1000 mg dietary phytate/d. Intestinal excretion of endogenous zinc is regulated in response to recent absorption and to zinc status. The quantitative relation of intestinal excretion of endogenous zinc to zinc absorption is currently considered to be of major importance in the determination of zinc requirements. The effects of phytate on intestinal losses of endogenous zinc merit further investigation but are probably not of the same magnitude as its inhibitory effects on absorption of exogenous zinc.

Dietary indicators for assessing the adequacy of population zinc intakes

The assessment of dietary zinc intakes is an important component of evaluating the risk of zinc deficiency in populations, and for designing appropriate food-based interventions, including fortification, to improve zinc intakes. The prevalence of inadequate zinc intakes can describe the relative magnitude of the risk of zinc deficiency in the population and identify subpopulations at elevated risk. As a cornerstone to evaluating the adequacy of population zinc intakes globally, a set of internationally appropriate dietary reference intakes must be defined. The World Health Organization/Food and Agriculture Organization/International Atomic Energy Agency (WHO/FAO/IAEA) and the Food and Nutrition Board/US Institute of Medicine (FNB/IOM) have presented estimated average requirements (EAR) for dietary zinc intake, and, more recently, the International Zinc Nutrition Consultative Group (IZiNCG) presented a revised set of recommendations for international use. A prevalence of inadequate zinc intakes greater than 25% is considered to represent an elevated risk of population zinc deficiency. As the requirement estimates are derived from smaller, clinical studies and, for children, most components of the estimates are extrapolated from data for adults, it was desirable to evaluate their internal validity. The estimated physiological requirements for adult men and women appear to adequately predict zinc status as determined by biochemical indicators of status and/or zinc balance. With the use of data from available studies, the reported prevalence of low serum zinc concentration and the estimated prevalence of inadequate zinc intakes predict similar levels of risk of zinc deficiency, particularly among pregnant and nonpregnant women. Conformity between these two indicators is less consistent for children, suggesting that further data and/or direct studies of zinc requirements among children are needed.

Does ageing affect zinc homeostasis and dietary requirements?

Dietary intakes of zinc are lower in the elderly because of reduced energy requirements, and it is not clear whether ageing impacts on adaptive homeostatic mechanisms, namely absorptive efficiency and endogenous losses in the GI tract. Physiological requirements for zinc are unlikely to change significantly, but there are several attributes of ageing that may affect aspects of zinc metabolism (e.g. changes in gut structure and function, disease states, chronic inflammation, epigenetic changes in genes that express zinc-related proteins and drug regimens) that are worthy of further investigation. There is, as yet, no information on the effects of ageing on zinc transporters, and there are no sensitive and specific measures of zinc status, therefore dietary recommendations for zinc have been derived from factorial calculations using information on zinc absorption and loss, and estimates of dietary bioavailability.

Zinc and iron bioavailability of genetically modified soybeans in rats

The aim of this work was to evaluate zinc and iron bioavailability of UFV-116, a new variety without 2 lipoxygenases, with better taste and flavor than a commercial variety OCEPAR 19, containing all 3 isozymes. To evaluate zinc absorption using 65Zn whole body retention and femur 65Zn uptake, rats were given 3 g of a 65ZnCl2 labeled test meal (0.25 microCi). The 2 varieties were tested at the level of 9 and 30 ppm of zinc as defatted soy flour. Two other groups (control) received egg white as source of protein and ZnS04.H20 as the zinc source. To evaluate iron absorption, using 59Fe whole body retention, animals were given a 3 g 59FeCl3 labeled test meal (0.2 microCi). The 2 varieties were tested at 12 and 25 ppm iron as defatted soy flour. Whole fat soy flour of variety 1 (UFV-116) was higher (P < 0.05) in Ca, K, Mg, phytic acid, and oxalate than variety 2 (OCEPAR-19). No difference was observed among the soybean varieties (P > 0.05) for femur 65Zn retention, at different levels of zinc. However, whole body retention was lower (P < 0.05) for UFV-116 than for OCEPAR-19. Femur 65Zn uptake was correlated with the whole body retention; however, whole body retention was more sensitive. Whole body 59Fe retention from UFV-116 was lower (P < 0.05) than from OCEPAR-19. Zinc and iron bioavailability was lower for UFV-116, possibly due to its higher content of antinutrient factors, especially phytate.

Zinc homeostasis in 1–4 year olds consuming diets typical of US children

Few data have evaluated Zn balance in young children after the first year of life. The objective of the present study was to study the relationships among Zn intake, absorption, endogenous faecal excretion, and retention in a group of healthy children. Thirty children, aged 15–48 months, were studied on a diet representative of their usual daily mineral intake. Zn absorption was assessed using a dual-tracer stable-isotope technique. Endogenous Zn faecal excretion and Cu absorption were determined in a subset of children. We found that Zn intake from the in-patient weighed dietary record (5·0 (sd 2·1) mg/d) was significantly greater than the current estimated average requirement (EAR; 2·5 mg/d; P < 0·0001). Neither fractional Zn absorption, urinary Zn excretion, nor endogenous faecal Zn excretion was significantly related to Zn intake (r2 < 0·1; P>0·4, for all). Absolute Zn absorption was significantly related to Zn intake (r2 0·696; P < 0·0001), as was Zn retention (r2 0·506; P < 0·0001). Cu absorption was relatively high (75·1 (sd 10·8) %) despite the high Zn intake. The EAR for Zn based on this dataset would appear to be between 4·2 and 4·7 mg/d to allow for a net average retention of 120 μg/d consistent with growth needs. We concluded that at relatively high Zn intakes there was little evidence of down regulation of absorption or up regulation of urinary or endogenous faecal Zn excretion across the intake range studied. Zn retention was positively correlated with intake. A Zn intake between 4·2 and 4·7 mg/d should meet the requirement for normal growth for this age group.

A mathematical model of zinc absorption in humans as a function of dietary zinc and phytate

The quantities of zinc and phytate in the diet are the primary factors determining zinc absorption. A mathematical model of zinc absorption as a function of dietary zinc and phytate can be used to predict dietary zinc requirements and, potentially, enhance our understanding of zinc absorption. Our goal was to develop a model of practical and informative value based on fundamental knowledge of the zinc absorption process and then fit the model to selected published data to assess its validity and estimate parameter values. A model of moderate mathematical complexity relating total zinc absorption to total dietary zinc and total dietary phytate was derived and fit to 21 mean data from whole day absorption studies using nonlinear regression analysis. Model validity, goodness of fit, satisfaction of regression assumptions, and quality of the parameter estimates were evaluated using standard statistical criteria. The fit had an R(2) of 0.82. The residuals were found to exhibit a normal distribution, constant variance, and independence. The parameters of the model, A(MAX), K(R), and K(P), were estimated to have values of 0.13, 0.10, and 1.2 mmol/d, respectively. Several of these estimates had wide CI attributable in part to the small number and the scatter of the data. The model was judged to be valid and of immediate value for studying and predicting absorption. A version of the model incorporating a passive absorption mechanism was not supported by the available data.

Zinc absorption during late pregnancy in rural southern Ethiopia

BACKGROUND

Little is yet known about zinc absorption in late pregnancy, and no information on absorption from the total diet is available.

OBJECTIVE

The objective was to measure the fractional absorption of zinc (FAZ) and to estimate the total quantity of absorbed zinc (TAZ) each day during the third trimester of pregnancy in poor rural southern Ethiopian women.

DESIGN

The participants (n = 17) were a convenience sample from a larger study population. The third stage of pregnancy was estimated from fundal height by the Bushulo Health Center prenatal outreach program. FAZ was determined with a dual-isotope tracer ratio technique that uses measurements of urine enrichment with zinc stable isotopes administered intravenously and orally, as an extrinsic label, with all meals in 1 d. Total dietary zinc (TDZ) was calculated from weighed diet records and Ethiopian food-composition tables supported by zinc and phytate analyses of major food items for individual meals. Plasma zinc and exchangeable zinc pool size were also estimated.

RESULTS

Mean (+/-SD) FAZ was 0.35 +/- 0.11, TDZ was 6.0 +/- 3.2 mg/d, TAZ was 2.1 +/- 1.0 mg/d, phytate intake was 1033 +/- 843 mg/d, plasma zinc was 44.1 +/- 6.0 microg/dL, and the exchangeable zinc pool size was 142 +/- 39 mg. The molar ratio of phytate to zinc was 17:1.

CONCLUSIONS

Women from a poor rural population who were dependent on a moderately high-phytate diet had low TDZ and low plasma zinc concentrations in the third trimester of pregnancy. TAZ was modestly higher than that predicted but did not meet physiologic requirements.

Changes in zinc absorption during development

Zinc (Zn) nutrition is of special practical importance in infants and young children, however relatively little is known about maturation and comparative aspects of Zn absorption. The principal objective of this paper is to compare Zn absorption of term infants, preterm infants, and adults on low phytate diets. Existing data derived from using Zn stable isotopes as extrinsic labels for an entire day were modeled with saturation kinetic analysis (saturable response model). When adjusted for differences in length of small intestine, the efficiency of Zn absorption for both term (4 months) and preterm (33 weeks post-conception) infants was comparable with that for adults, suggesting early maturation of mechanisms that regulate absorption. However, infant intestinal lengths were shorter, and Zn absorptive capacity was proportionately less. Reduced capacity was matched by lower Zn requirements for normal term infants. This favorable match, however, did not occur in the preterm infant because of relatively high Zn requirements. Although intestinal conservation of endogenous Zn in these preterm infants was appropriate in relation to the quantity of Zn absorbed, it was not optimal for achieving the retention required. Normal homeostatic mechanisms in the premature infant prevented efficient absorption of the quantity of Zn required or/and optimal conservation of endogenous Zn.