Stable isotope studies of zinc absorption and retention in young and elderly men

The art of establishing mineral tolerances of dogs and cats

For over six decades, nutritional science has provided well-developed, peer-reviewed nutrient recommendations to support the health of dogs and cats. These guidelines are updated based on new scientifically valid research and appropriate peer-review. Recent regulatory and scientific positions around health issues have resulted in strong opinions and desires for rapid regulatory action surrounding mineral nutrition, but with limited and conflicting scientific evidence. Pet Food Institute nutrition experts have come together to jointly author an article on the complexities of establishing mineral tolerances of dogs and cats to illustrate the limitations in defining mineral tolerances. This discussion covers how mineral requirements were determined, including the opportunities and pitfalls encountered. Scientific councils must review and clarify any proposed changes in conducting mineral nutrition research that might impact complete and balanced foods and surrounding regulations. It is important to clarify the multiple issues in mineral nutrition research and the necessity for thorough evaluation of data while avoiding arbitrary and potentially harmful guidelines.

Exploring the potential function of trace elements in human health: a therapeutic perspective

A trace element, known as a minor element, is a chemical element whose concentration is very low. They are divided into essential and non-essential classes. Numerous physiological and metabolic processes in both plants and animals require essential trace elements. These essential trace elements are so directly related to the metabolic and physiologic processes of the organism that either their excess or deficiency can result in severe bodily malfunction or, in the worst situations, death. Elements can be found in nature in various forms and are essential for the body to carry out its varied functions. Trace elements are crucial for biological, chemical, and molecular cell activity. Nutritional deficits can lead to weakened immunity, increased susceptibility to oral and systemic infections, delayed physical and mental development, and lower productivity. Trace element enzymes are involved in many biological and chemical processes. These compounds act as co-factors for a number of enzymes and serve as centers for stabilizing the structures of proteins and enzymes, allowing them to mediate crucial biological processes. Some trace elements control vital biological processes by attaching to molecules on the cell membrane's receptor site or altering the structure of the membrane to prevent specific molecules from entering the cell. Some trace elements are engaged in redox reactions. Trace elements have two purposes. They are required for the regular stability of cellular structures, but when lacking, they might activate alternate routes and induce disorders. Therefore, thoroughly understanding these trace elements is essential for maintaining optimal health and preventing disease.

Zinc and aging: a narrative review of the effects on hematopoiesis and its link with diseases

There has been a global increase in the older population in recent decades and, as age advances, complex metabolic and epigenetic changes occur in the organism, and these may trigger some health complications commonly found among this population. Additionally, several changes occur in older people that can reduce the dietary intake or the process of nutrient absorption. In this way, tissues with high nutrient requirements are more affected. Hematopoiesis is the process of formation, development, and maturation of blood cells and is a process with a high turnover. This high demand makes the integrity of the hematopoietic process susceptible to various factors that impair physiological function, such as aging and micronutrient bioavailability. Among these micronutrients, Zinc is considered an important micronutrient, playing diverse roles across various tissues and cell types. Some of the alterations in hematopoiesis that appear as a consequence of aging and due to insufficient micronutrient intake are well described in the literature; however, not much is known about how zinc deficiency contributes towards the development of diseases seen in aging. Considering the importance of zinc to act on several biological processes, this narrative review discusses several studies related to the physiological requirements, deficiency, or excess of zinc, including studies in experimental models and humans, and aimed to shed light on the relationship between zinc and the regulation of hematopoietic tissue, exploring possible links between this mineral with common disorders that appear during aging.

Can Zinc Supplementation Attenuate High Fat Diet-Induced Non-Alcoholic Fatty Liver Disease?

The pathogenesis of non-alcoholic fatty liver disease (NAFLD), the most prevalent chronic liver disease, is associated with zinc deficiency. Previous studies show zinc supplementation improves steatosis and glucose metabolism, but its therapeutic effects in patients with established NAFLD remain unclear. We developed an in vivo model to characterize the effects of zinc supplementation on high-fat diet (HFD) induced NAFLD and hypothesized that the established NAFLD would be attenuated by zinc supplementation. Male C57BL/6J mice were fed a control diet or HFD for 12 weeks. Mice were then further grouped into normal and zinc-supplemented diets for 8 additional weeks. Body composition and glucose tolerance were determined before and after zinc supplementation. At euthanasia, plasma and liver tissue were collected for characterization and downstream analysis. As expected, 12 weeks of HFD resulted in reduced glucose clearance and altered body composition. Eight weeks of subsequent zinc supplementation did not alter glucose handling, plasma transaminases, steatosis, or hepatic gene expression. Results from our model suggest 8-week zinc supplementation cannot reverse established NAFLD. The HFD may have caused NAFLD disease progression beyond rescue by an 8-week period of zinc supplementation. Future studies will address these limitations and provide insights into zinc as a therapeutic agent for established NAFLD.

Age and micronutrient effects on the microbiome in a mouse model of zinc depletion and supplementation

Older adult populations are at risk for zinc deficiency, which may predispose them to immune dysfunction and age-related chronic inflammation that drives myriad diseases and disorders. Recent work also implicates the gut microbiome in the onset and severity of age-related inflammation, indicating that dietary zinc status and the gut microbiome may interact to impact age-related host immunity. We hypothesize that age-related alterations in the gut microbiome contribute to the demonstrated zinc deficits in host zinc levels and increased inflammation. We tested this hypothesis with a multifactor two-part study design in a C57BL/6 mouse model. The two studies included young (2 month old) and aged (24 month old) mice fed either (1) a zinc adequate or zinc supplemented diet, or (2) a zinc adequate or marginal zinc deficient diet, respectively. Overall microbiome composition did not significantly change with zinc status; beta diversity was driven almost exclusively by age effects. Microbiome differences due to age are evident at all taxonomic levels, with more than half of all taxonomic units significantly different. Furthermore, we found 150 out of 186 genera were significantly different between the two age groups, with Bacteriodes and Parabacteroides being the primary taxa of young and old mice, respectively. These data suggest that modulating individual micronutrient concentrations does not lead to comprehensive microbiome shifts, but rather affects specific components of the gut microbiome. However, a phylogenetic agglomeration technique (ClaaTU) revealed phylogenetic clades that respond to modulation of dietary zinc status and inflammation state in an age-dependent manner. Collectively, these results suggest that a complex interplay exists between host age, gut microbiome composition, and dietary zinc status.

Creating person-al space for unspoken voices during diagnostic medical imaging examinations: a qualitative study

Background

There is emerging interest in person-centred care within a short-lived yet complex medical imaging encounter. This study explored this event from the viewpoint of patients referred for an imaging examination, with a focus on the person and their person-al space.

Methods

We used convenience sampling to conduct semi-structured interviews with 21 patients in a private medical imaging practice in Australia. The first phase of data analysis was conducted deductively, using the six elements of the person-centred, patient-journey framework of the Australian Commission on Safety and Quality in Healthcare: transition in; engagement; decisions; well-being; experience; and transition out. This was followed by inductive content analysis to identify overarching themes that span a patient’s journey into, through and out of an imaging encounter.

Results

The transition-in phase began with an appointment and the first point of contact with the imaging department at reception. Engagement focused on patient-radiographer interactions and explanations to the patient on what was going to happen. Decisions related primarily to radiographers’ decisions on how to conduct a particular examination and how to get patient cooperation. Participants’ well-being related to their appreciation of gentle treatment; they also referred to past negative experiences that had made a lasting impression. Transitioning out of the imaging encounter included the sending of the results to the referring medical practitioner. Person-al vulnerabilities emerged as a cross-cutting theme. Patients’ vulnerability, for which they needed reassurance, pertained to uncertainties about the investigation and the possible results. Healthcare professionals were vulnerable because of patient expectations of a certain demeanour and of pressure to perform optimal quality investigations. Lastly, patients’ personal lives, concerns and pressures – their person-al ‘baggage’ – shaped their experience of the imaging encounter.

Conclusion

To add value to the quality of the service they deliver, radiography practitioners should endeavour to create a person-al space for clients. Creating these spaces is complex as patients are not in a position to judge the procedures required by technical imaging protocols and the quality control of equipment. A reflective tool is proposed for radiographers to use in discussions with their team and its leaders on improving person-centred care and the quality of services in their practice.

Multiple Micronutrients, Including Zinc, Selenium and Iron, Are Positively Associated with Anemia in New Zealand Aged Care Residents

Anemia is a significant comorbidity for older adults not fully attributable to iron deficiency. Low-grade inflammation and other micronutrient deficiencies also contribute. This cross-sectional study examined the relationships between nutrient and non-nutrient factors with hemoglobin and anemia in 285 residents (>65 years) of 16 New Zealand aged-care facilities. Blood samples were analyzed for hemoglobin, ferritin, sTfR, hepcidin, zinc, selenium, and interleukin-6 (IL-6), (with ferritin, sTfR, zinc and selenium adjusted for inflammation). Linear regression models examined the relationships between micronutrient biomarkers (iron, zinc, selenium, vitamin B-12 and D), age, sex, and health factors with hemoglobin. Thirty-two percent of participants exhibited anemia, although <2% had either depleted iron stores or iron deficiency. Plasma zinc and selenium deficiencies were present in 72% and 38% of participants, respectively. Plasma zinc and total body iron (TBI) were positively associated (p < 0.05) with hemoglobin, while gastric acid suppressing medications, hepcidin, and interleukin-6 were inversely associated. These relationships were maintained after the application of anemia cut-offs. These findings emphasize the importance of considering multiple micronutrient deficiencies as risk factors for anemia.

Effects of zinc status on age-related T cell dysfunction and chronic inflammation

Age-related T cell dysfunction contributes to immunosenescence and chronic inflammation. Aging is also associated with a progressive decline in zinc status. Zinc is an essential micronutrient critical for immune function. A significant portion of the older populations are at risk for marginal zinc deficiency. The combined impact of dietary zinc deficiency and age on immune dysfunction has not been well explored despite the common occurrence together in the elderly population. We hypothesize that age-related zinc loss contributes to T cell dysfunction and chronic inflammation in the elderly and is exacerbated by inadequate dietary intake and improved with zinc supplementation. Using an aging mouse model, the effects of marginal zinc deficiency and zinc supplementation on Th1/Th17/proinflammatory cytokine profiles and CD4⁺ T cell naïve/memory phenotypes were examined. In the first study, young (2 months) and old (24 months) C57BL/6 mice were fed a zinc adequate (ZA) or marginally zinc deficient (MZD) diets for 6 weeks. In the second study, mice were fed a ZA or zinc supplemented (ZS) diet for 6 weeks. MZD old mice had significant increase in LPS-induced IL6 compared to ZA old mice. In contrast, ZS old mice had significantly reduced plasma MCP1 levels, reduced T cell activation-induced IFNγ, IL17, and TNFα response, as well as increased naïve CD4⁺ T-cell subset compared to ZA old mice. Our data suggest that zinc deficiency is an important contributing factor in immune aging, and improving zinc status can in part reverse immune dysfunction and reduce chronic inflammation associated with aging.

A Guide to Human Zinc Absorption: General Overview and Recent Advances of In Vitro Intestinal Models

Zinc absorption in the small intestine is one of the main mechanisms regulating the systemic homeostasis of this essential trace element. This review summarizes the key aspects of human zinc homeostasis and distribution. In particular, current knowledge on human intestinal zinc absorption and the influence of diet-derived factors on bioaccessibility and bioavailability as well as intrinsic luminal and basolateral factors with an impact on zinc uptake are discussed. Their investigation is increasingly performed using in vitro cellular intestinal models, which are continually being refined and keep gaining importance for studying zinc uptake and transport via the human intestinal epithelium. The vast majority of these models is based on the human intestinal cell line Caco-2 in combination with other relevant components of the intestinal epithelium, such as mucin-secreting goblet cells and in vitro digestion models, and applying improved compositions of apical and basolateral media to mimic the in vivo situation as closely as possible. Particular emphasis is placed on summarizing previous applications as well as key results of these models, comparing their results to data obtained in humans, and discussing their advantages and limitations.

Trace Elements in Human Nutrition (II) - An Update

The dietary requirement for an essential trace element is an intake level which meets a specified criterion for adequacy and thereby minimizes risk of nutrient deficiency or excess. Disturbances in trace element homeostasis may result in the development of pathologic states and diseases. This article is an update of a review article “Trace Elements in Human Nutrition-A Review” previously published in 2013. The previous review was updated to emphasis in detail the importance of known trace elements so far in humans’ physiology and nutrition and also to implement the detailed information for practical and effective management of trace elements’ status in clinical diagnosis and health care situations. Although various classifications for trace elements have been proposed and may be controversial, this review will use World Health Organization( WHO) classification as previously done. For this review a traditional integrated review format was chosen and many recent medical and scientific literatures for the new findings on bioavailability, functions, and state of excess/deficiency of trace elements were assessed. The results indicated that for the known essential elements, essentiality and toxicity are unrelated and toxicity is a matter of dose or exposure. Little is known about the essentiality of some of the probably essential elements. In regard to toxic heavy metals, a toxic element may nevertheless be essential. In addition, the early pathological manifestations of trace elements deficiency or excess are difficult to detect until more specific pathologically relevant indicators become available. Discoveries and many refinements in the development of new techniques and continual improvement in laboratory methods have enabled researchers to detect the early pathological consequences of deficiency or excess of trace elements. They all are promises to fulfill the gaps in the present and future research and clinical diagnosis of trace elements deficiencies or intoxications. However, further investigations are needed to complete the important gaps in our knowledge on trace elements, especially probably essential trace elements’ role in health and disease status.

Role of Zinc and Selenium in Oxidative Stress and Immunosenescence: Implications for Healthy Aging and Longevity

Aging is a complex process that includes gradual and spontaneous biochemical and physiological changes which contributes to a decline in performance and increased susceptibility to diseases. Zn and Se are essential trace elements that play a pivotal role in immune functions and antioxidant defense and, consequently, are claimed to play also a role in successful aging trajectories. Consistently with their nature of essential trace elements, a plethora of data obtained “in vitro” and “in vivo” (in humans and animal models) support the relevance of Zn and Se for both the innate and adoptive immune response. Moreover, Zn and Se are strictly involved in the synthesis and regulation of activity of proteins and enzymes, e.g., metallothioneins (MT) and glutathione peroxidase (GPX), that are necessary for our endogenous antioxidant response. This is clearly important to protect our cells from oxidative damage and to slow the decline of our immune system with aging. Age-related changes affecting tissue levels of Zn and Se may indicate that the risk of Zn and Se deficiency increases with aging. However, it is still unclear which of these changes can be the consequence of a “real deficiency” and which can be part of our physiological compensatory response to the accumulating damage occurring in aging. Furthermore, the upregulation of antioxidant proteins (Zn and Se dependent) may be a manifestation of self-induced oxidative stress. By the way, Zn and Se dependent proteins are modulated not only by nutritional status, but also by well-known hallmarks of aging that play antagonistic functions, such as the deregulated nutrient sensing pathways and cellular senescence. Thus, it is not an easy task to conduct Zn or Se supplementation in elderly and it is emerging consistent that these kind of supplementation requires an individualized approach. Anyway, there is consistent support that supplementation with Zn using doses around 10 mg/day is generally safe in elderly and may even improve part of immune performances in those subjects with a baseline deficiency. Regarding Se supplementation, it may induce both beneficial and detrimental effects on cellular immunity depending on the form of Se, supplemental dose, and delivery matrix. The nutritional association of supplements based on “Zn plus Se” is hypothesized to provide additional benefits, but this will likely need a more complex individualized approach. The improvement of our knowledge around screening and detection of Zn and Se deficiency in aging could lead to substantial benefits in terms of efficacy of nutritional supplements aimed at ameliorate performance and health in aging.

Effects of Multivitamin and Multimineral Supplementation on Blood Pressure: A Meta-Analysis of 12 Randomized Controlled Trials

Previous studies have not drawn a consistent conclusion about effect of multivitamin and multimineral supplementation (MVMS) on blood pressure. A comprehensive search of PubMed, Embase and Cochrane Library (up to May 2018) and references of relevant articles was undertaken. The present meta-analysis included 12 randomized controlled trials (RCTs), of which eight RCTs in 2011 subjects evaluated the effect of MVMS on blood pressure and four RCTs in 21,196 subjects evaluated the effect of MVMS on the risk of hypertension. MVMS had a lowering effect on systolic blood pressure (SBP) and diastolic blood pressure (DBP): the weighted mean difference (WMD) was -1.31 mmHg (95% CI, -2.48 to -0.14 mmHg) and -0.71 mmHg (95% CI, -1.43 to 0.00 mmHg), respectively. Subgroup analysis indicated that the lowering effect of MVMS on blood pressure was only significant in 134 subjects with chronic disease but not in 1580 healthy subjects, and the WMD for systolic blood pressure (SBP) and DBP in subjects with chronic disease was -6.29 mmHg (95% CI, -11.09 to -1.50 mmHg) and -2.32 mmHg (95% CI, -4.50 to -0.13 mmHg), respectively. The effect size of MVMS on SBP in 58 hypertensive subjects (WMD, -7.98 mmHg; 95% CI, -14.95 to -1.02 mmHg) was more than six times of that in 1656 normotensive subjects (WMD, -1.25 mmHg; 95% CI, -2.48 to -0.02 mmHg). However, no significant effect on DBP was observed in both hypertensive and normotensive subgroups. There was no significant effect of MVMS on risk of hypertension in 22,852 subjects with a normal blood pressure at baseline. In conclusion, although MVMS had a significant lowering effect on blood pressure in normotensive subjects, the lowering effect was too small to effectively prevent future hypertension. MVMS may be an effective method for blood pressure control in subjects with chronic disease including hypertension, but the sample size of subjects with hypertension or other chronic disease was too small, and more well-designed RCTs are needed to confirm this result.

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.

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.

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 and the aging brain

Alterations in trace element homeostasis could be involved in the pathology of dementia, and in particular of Alzheimer's disease (AD). Zinc is a structural or functional component of many proteins, being involved in numerous and relevant physiological functions. Zinc homeostasis is affected in the elderly, and current evidence points to alterations in the cellular and systemic distribution of zinc in AD. Although the association of zinc and other metals with AD pathology remains unclear, therapeutic approaches designed to restore trace element homeostasis are being tested in clinical trials. Not only could zinc supplementation potentially benefit individuals with AD, but zinc supplementation also improves glycemic control in the elderly suffering from diabetes mellitus. However, the findings that select genetic polymorphisms may alter an individual's zinc intake requirements should be taken into consideration when planning zinc supplementation. This review will focus on current knowledge regarding pathological and protective mechanisms involving brain zinc in AD to highlight areas where future research may enable development of new and improved therapies.

Zinc and its role in age-related inflammation and immune dysfunction

Zinc is an essential micronutrient required for many cellular processes, especially for the normal development and function of the immune system. Zinc homeostasis and signaling are critical in immune activation, and an imbalance in zinc homeostasis is associated with the development of chronic diseases. Zinc deficiency causes significant impairment in both adaptive and innate immune responses, and promotes systemic inflammation. The elderly are a population particularly susceptible to zinc deficiency. National surveys indicate that a significant portion of the aged population has inadequate zinc intake, and a decline in zinc status is observed with age. There are remarkable similarities between the hallmarks of zinc deficiency and immunological dysfunction in aged individuals. Both zinc deficiency and the aging process are characterized by impaired immune responses and systemic low grade chronic inflammation. It has been hypothesized that age-related zinc deficiency may be an important factor contributing to immune dysfunction and chronic inflammation during the aging process. In this review, we discuss the effects of zinc status on aging, potential molecular and epigenetic mechanisms contributing to age-related decline in zinc status, and the role of zinc in age-related immune dysfunction and chronic inflammation.

Plasma zinc but not the exchangeable zinc pool size differs between young and older Korean women

This study was done to determine the effect of age on zinc metabolism and status among healthy Korean women. Measures of zinc metabolism and status were measured in eight young women (22-24 years) and seven elderly women (66-75 years) consuming a typical Korean diet. Oral and intravenous tracers highly enriched in (67)Zn and (70)Zn were administered simultaneously. Multiple plasma, 24-h urines, and fecal samples were collected after isotope administration. In the young women, additional plasma were collected to determine zinc kinetics using a seven-compartmental model. Exchangeable Zinc Pool (EZP) was estimated by Miller's method. Plasma zinc concentrations were higher in older women than younger women (p < 0.05). EZP and urinary zinc tended to be higher in older women than younger women. Fractional and total zinc absorption and endogenous fecal zinc losses did not differ between young and older women. A comparison of the zinc kinetics of the Korean and American women showed no differences in plasma or EZP zinc parameters. However, absorbed zinc and zinc flux to slowly turning over tissues (Q7) were lower in Korean women than that of Americans (p < 0.01) suggesting the total body zinc content of Korean women is lower than that of American women.

Zinc, metallothioneins and immunosenescence: effect of zinc supply as nutrigenomic approach

Ageing is an inevitable biological process associated with gradual and spontaneous biochemical and physiological changes and increased susceptibility to diseases. Nutritional factor, zinc, known to be involved in improving immunity, may remodel some of the age-associated changes, leading to a healthy ageing. "In Vitro" studies involving human lymphocytes exposed to endotoxins, and "in vivo" studies comparing old and young mice fed with low dietary zinc suggest that zinc is important for both innate and adaptive immune efficiency, and more optimal inflammatory/immune response. The intracellular zinc homeostasis is mainly regulated by Metallothioneins (MT), via ion release through the reduction of thiol groups in MT molecule. These processes are crucial because mediating the zinc signalling within the immune cells assigning to zinc a role of "second messenger". Zinc homeostasis is altered in ageing partly due to higher expression levels of MT, leading to an increased sequestration of zinc, resulting in less availability of free intracellular zinc. Improvement of immune functions and stress response systems occurs in elderly after physiological zinc supplementation. The main reason behind these effects seems to be related to a like "hormetic" response induced by zinc. However, the choice of old subjects for zinc supplementation has to be performed in relationship to the specific genetic background of MT and pro-inflammatory cytokine (IL-6) because the latter is involved both in MT gene expression and in intracellular zinc homeostasis. Old subjects carrying GG genotypes (termed C- carriers) in IL-6--174G/C locus display increased IL-6 production, low intracellular zinc ion availability, impaired innate immune response and enhanced MT. By contrast, old subjects carrying GC and CC genotypes (termed C+ carriers) in the same IL-6--174 locus displayed satisfactory intracellular zinc and innate immune response. Moreover, male carriers of C+ allele are more prone to reach centenarian age than C- ones. Therefore, old C- subjects are likely to benefit more from zinc supplementation restoring NK cell cytotoxicity and improving the zinc status. Plasma zinc deficiency and the altered immune response is more evident when the genetic variations of IL-6 polymorphism are associated with the genetic variations of MT1A in position +647, suggesting that the genetic variations of IL-6 and MT1A are very useful tools for the identification of old people who effectively need zinc supplementation.

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.

The use of dysprosium to measure endogenous zinc excretion in feces eliminates the necessity of complete fecal collections

The secretion of endogenous zinc (Zn) into the gut and subsequent excretion in the feces is understood to play a major role in maintaining Zn homeostasis in humans. Therefore, the measurement of endogenous Zn losses in the feces (EFZ) can be an important aspect of the study of Zn metabolism and homeostasis. The methods currently used to measure EFZ have the disadvantage of requiring complete fecal collections over multiple days. We have investigated the use of dysprosium (Dy), a nonabsorbable rare earth metal, in a method of determining EFZ that does not require complete fecal collections and permits the measurement of EFZ from several fecal samples. The method was evaluated using data from a study of free-living adult females in which Dy was administered 3-4 times/d over a period of 5 or 6 d to monitor completeness of fecal collections. The results did not differ from those obtained using an established isotope dilution method. We found that the measurement of the sample Dy:Zn ratio was useful for selecting samples for measurement. We conclude that the Dy method of determining EFZ is a valid and less burdensome alternative to current techniques.

The relation between reduced serum melatonin levels and zinc in rats with induced hypothyroidism

The objective of the study was to explore the changes in melatonin and zinc levels in rats with induced hypothyroidism. Thirty adult male rats used in the study were allocated to three groups with equal numbers. Group 1: General control group which was not subjected to any procedure. Group 2: Sham-hypothyroidism group to which was administered 10 mg kg(-1) intraperitoneal (i.p.) physiologic saline (0.09% NaCl) for 4 weeks. Group 3: Hypothyroidism group which was supplemented with intraperitoneal 10 mg kg(-1) propylthiouracil (PTU) for 4 weeks. Blood samples collected from all animals at the end of the study by decapitation were analysed for serum Total T4 (TT4), Total T3 (TT3), Free T4 (FT4), Free T3 (FT3) (ELISA) as well as for melatonin (RIA) hormones and zinc levels (atomic emission). Comparison of the study groups in terms of thyroid hormones, melatonin and zinc levels showed that TT4, TT3, FT4, FT3, melatonin and zinc levels in group 3 were lower than those in groups 1 and 2 (p < 0.01). These parameters were not different in groups 1 and 2. The results of the study demonstrate that PTU supplementation for 4 weeks results in a significant inhibition in both melatonin and zinc levels. Inhibited melatonin levels may result from the decrease in zinc levels.

Relationships between faecal phytate and mineral excretion depend on dietary phytate and age

We investigated the adverse effect of phytate on mineral absorption and the effect of dietary phytate and age on the relationship between faecal phytate and faecal mineral excretion. Fourteen young women (aged 19–24 years) and fourteen elderly women (64–75 years) were studied for two metabolic periods (MP). In MP1, the subjects consumed a controlled high-phytate (HP) diet for 10 d; in MP2, they were on a low-phytate (LP) diet for 10 d. In each period, diet samples and complete faecal samples for 5 d were collected to analyse phytate and mineral contents. Mineral concentrations in diet and faeces were measured by inductively coupled plasma–atomic emission spectrometry. Linear regression analysis was used to examine the associations between faecal phytate and mineral excretion. The degradation rate of dietary phytate was about 77 % for young women, which was significantly lower than that of elderly women (86 %) (P < 0·05). Faecal phytate excretion was positively correlated with mineral excretion (Ca, P, Fe and Zn) in both the HP and LP diet groups in young women (P < 0·05). The linear relationship tended to be greater during the LP diet period compared with the HP diet period in young women. However, no association was found between phytate excretion and mineral excretion in elderly women. In summary, undegraded dietary phytate (10–20 %) had a negative effect on mineral absorption in young women, and the relationship between faecal phytate and mineral excretion was affected by both dietary phytate and age.

Does promoter methylation of the SLC30A5 (ZnT5) zinc transporter gene contribute to the ageing-related decline in zinc status?

A decline in Zn status with ageing may contribute to the development of frailty, including impaired immune function, and increased incidence of age-related degenerative diseases. This decline may be a result of reduced dietary Zn intake and/or impaired Zn absorption in the gut. The Zn transporter ZnT5 may play a key role in the absorption of dietary Zn. The corresponding gene (SLC30A5) has a CpG island in its promoter region, so could be regulated by epigenetic mechanisms. It is hypothesised that methylation of the SLC30A5 promoter region is increased with age and that a resulting reduction in ZnT5 expression contributes to the decline in Zn status observed with ageing. This hypothesis has been addressed through (1) studies of effects of SLC30A5 promoter methylation on gene expression in vitro and (2) in vivo measurements of the DNA methylation status of this gene domain. It has been established in vitro that methylation of the human SLC30A5 promoter region results in reduced expression of an associated reporter gene. Second, this gene region shows variable levels of methylation in vivo. Correlation between the level of methylation at this locus and age would support the hypothesis that age-related hypermethylation of this region has the potential to modulate dietary Zn absorption. This premise is being investigated by analysis of additional samples from a human adult cohort to test the hypothesis that methylation of the SLC30A5 promoter region contributes to the age-related decline in Zn status.

Role of Zinc and Selenium in Oxidative Stress and Immunosenescence: Implications for Healthy Ageing and Longevity

Ageing is an inevitable biological process with gradual and spontaneous biochemical and physiological changes and increased susceptibility to diseases. Some nutritional factors (zinc and selenium) may remodel these changes leading to a possible escaping of diseases with subsequent healthy ageing, because they are especially involved in improving immune functions as well as antioxidant defense. Experiments performed “in vitro” (human lymphocytes exposed to endotoxins) and “in vivo” (old mice or young mice fed with low zinc dietary intake) show that zinc is important for immune response both innate and adoptive. Selenium provokes zinc release by Metallothioneins (MT), via reduction of glutathione peroxidase. This fact is crucial in ageing because high MT may be unable to release zinc with subsequent low intracellular free zinc ion availability for immune response. Taking into account the existence of zinc transporters (ZnT and ZIP family) for cellular zinc efflux and influx, respectively, the association between ZnT and MT is important in maintaining satisfactory intracellular zinc homeostasis in ageing. Improved immune performance occur in elderly after physiological zinc supplementation, which also induces prolonged survival in old, nude and neonatal thymectomized mice. The association “zinc plus selenium” improves humoral immunity in old subjects after influenza vaccination. Therefore, zinc and selenium are relevant for immunosenescence in order to achieve healthy ageing and longevity.

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.

Effect of zinc supplementation on vitamin status of middle-aged and older European adults: the ZENITH study

OBJECTIVE

To assess the effects of zinc supplementation on vitamin status in middle-aged and older volunteers.

SUBJECTS/METHODS

Three hundred and eighty-seven healthy middle-aged (55-70 years) and older (70-85 years) men and women, randomly allocated to three groups to receive 15 or 30 mg Zn/day or placebo for 6 months. Dietary intake was assessed by means of a validated 4-day recall record. Fasting blood samples were simultaneously analysed for levels of plasma retinol and alpha-tocopherol by high-performance liquid chromatography. Erythrocyte folates were measured by a competitive immunoassay with direct chemiluminescence detection on an automatized immunoanalyser. Biochemical measurements were performed at baseline and after 3 and 6 months of zinc supplementation.

RESULTS

Plasma vitamin A levels were significantly increased proportionally with zinc dose and period of treatment, particularly at 6 months (for 15 mg Zn/day, P<0.05; for 30 mg Zn/day, P<0.0001); no significant changes were observed in the placebo group. There was no effect of zinc supplementation on vitamin E/cholesterol ratio and erythrocyte folates.

CONCLUSIONS

Our results show that a long-term zinc supplementation increases plasma vitamin A levels in middle-aged and older people of similar characteristics to those involved in this study. Moreover, supplementation influences serum zinc levels but does not affect erythrocyte zinc concentration and both plasma vitamin E and erythrocyte folate status.

Effect of dietary phytate on zinc homeostasis in young and elderly Korean women

BACKGROUND

Previous studies suggest that consumption of predominantly plant-based diets with high phytate content contribute to zinc deficiency by inhibiting zinc absorption. Age of the individual may also affect the ability to maintain zinc homeostasis.

OBJECTIVE

This study was designed to determine the effect of dietary phytate on zinc homeostasis and to evaluate the effect of age on the capacity to maintain the zinc homeostasis with changes in dietary phytate in young and elderly Korean women.

DESIGN AND METHODS

Seven healthy young women (22-24 yr) and 10 healthy elderly women (66-75 yr) were studied consecutively for 3 months in 2 metabolic periods (MP) in two different metabolic units. During MP1 the women consumed a high phytate (HP) diet (P:Zn molar ratio = 23) for 9 days. After a 10 d wash-out period at home eating their usual diets, a lower phytate diet (LP) (P:Zn molar ratio = 10) was fed in MP2 for 9 d. Phytase was added to selected foods in the high phytate diet to reduce the phytate content of the meals in the LP period. The zinc content of both diets was about 6.5 mg/d. Stable isotopes of Zn ((70)Zn) were administered intravenously on d 5 of MP 1 and 2 for measuring endogenous fecal zinc excretion. Plasma samples were also collected on d 5 for measuring plasma zinc concentrations by Inductively Coupled Plasma-Atomic Emission Spectrometry (ICP-AES). 24 hr urine samples were collected for 5 d and complete fecal samples were collected for 9 d after isotope administration. Fractional zinc absorption (FZA) was calculated from mass balance corrected for endogenous fecal zinc (EFZ) excretion and EFZ was determined by using an isotopic dilution technique. Isotopic ratios for FZA and EFZ were measured by Inductively Coupled Plasma-Mass Spectrometry (ICP-MS). Statistical analyses were done using ANOVA.

RESULTS

Both the young and elderly women were in negative zinc balance during the HP period. This was due to a significant decrease in FZA and total absorbed zinc (TAZ) with a HP diet (43 vs 22% in young women, 34 vs 20% in elderly women, p < 0.001). EFZ excretion did not differ in the young and elderly women during the LP and HP periods. Dietary phytate did not alter plasma zinc concentrations or and urinary zinc excretion in either group.

CONCLUSIONS

Adjustments in zinc homeostasis with an increase in dietary phytate did not differ between young and elderly women in this study.

Effect of dietary phytic acid on zinc absorption in the healthy elderly, as assessed by serum concentration curve tests

Zn absorption was investigated in healthy elderly subjects aged 71–78 years and in young subjects aged 23–43 years using serum concentration curve (SCC) tests. Both groups had similar Zn and protein status. The increase in serum Zn was monitored for 180 min after ingestion of 200ml of soya milk enriched with 50mg of Zn. Three levels of phytic acid were used: 0g/200ml (totally dephytinized soya milk), 0.13 g/200ml (half dephytinized), and 0.26 g/200ml (natural phytic acid content). In a first study the effect of 0v.0.26 g/200 ml phytic acid was compared in 10 elderly and 10 young subjects, each subject receiving both treatments. In a second study soya milks with 0 and 0.13 g/200ml were tested in nine elderly and ten young subjects, again receiving both treatments. Mean areas under the curve of the SCC tests conducted with the 0 g/200 ml soya milk were found to be the same in both studies. Phytic acid strongly depressed Zn absorption in both studies (P≤ 0.05), but to a greater extent at the 0.26 g/200ml level. No difference was found between the groups of young and elderly subjects. Therefore, no significant effect of aging on Zn absorption, as evaluated by the SCC test, or on the inhibitory effect of phytic acid was detected.

Profiles of faecal output of rare earth elements and stable isotopic tracers of iron and zinc after oral administration

The objectives of this study were to confirm the non-absorbability and the reproducibility of faecal excretion kinetics of orally administered rare earth elements, and to investigate the excretion profiles of rare earth elements and stable isotopic tracers of Fe and Zn to establish the extent to which rare earth element markers duplicate the behaviour of isotopic tracers. Two investigations were performed: (1) six healthy subjects consumed a solution containing five rare earth elements in amounts varying from 1 to 10 mg; (2) seven healthy subjects were given a standard solution labelled with Sm marker and57Fe tracer, and a meal labelled with Yb marker and58Fe and70Zn tracers. Individual faecal samples were collected and analysed to determine recoveries of rare earth elements and unabsorbed isotopic tracers. The mean values for recoveries were 94·1 (SD 4·5) % FOR THE FIVE RARE EARTH ELEMENTS, AND 103 (sd 3·0) % and 99·8 (sd 2·8) % for Sm and Yb respectively. For Fe consumed with the solution, excretion kinetics of the rare earth element marker and unabsorbed tracers with cumulative collections of the first two and three faecal samples were identical, but endogenous excretion of Fe was significant (P<0·05) in stools collected after the third. For Fe and Zn consumed with the meal, the excretion kinetics for the first two individual faecal samples and composites of sequential outputs were identical. Rare earth elements can be used as markers in studies of measurement of absorption. The dose of tracer required for the measurement of absorption would be reduced proportionally to the reduction of the period of faecal sampling, so that studies with stable isotopes would be more economical, thus enabling epidemiological investigations.

Immunohistochemical Analysis of ZnT1, 4, 5, 6, and 7 in the Mouse Gastrointestinal Tract

Expression of five zinc transporters (ZnT1, 4, 5, 6, and 7) of the Slc30 family in the mouse gastrointestinal tract was studied by immunohistochemical analysis. Results demonstrated unique expression patterns, levels, and cellular localization among ZnT proteins in the mouse gastrointestinal tract with some overlapping. ZnT1 was abundantly expressed in the epithelium of the esophagus, duodenum of the small intestine, and cecum of the large intestine. ZnT4 was predominantly detected in the large intestine. ZnT5 was mainly expressed in the parietal cell of the stomach and in the absorptive epithelium of the duodenum and jejunum. ZnT6 was predominantly detected in the chief cell of the stomach, columnar epithelial cells of the jejunum, cecum, colon, and rectum. Lastly, ZnT7 was observed in all epithelia of the mouse gastrointestinal tract with the highest expression in the small intestine. Expression of ZnT proteins in the absorptive epithelial cell of the gastrointestinal tract suggests that ZnT proteins may play important roles in zinc absorption and endogenous zinc secretion.

Zinc-binding proteins (metallothionein and alpha-2 macroglobulin) and immunosenescence

Zinc is a relevant trace element for the efficiency of the entire immune system. The binding of zinc with some proteins, such as metallothioneins (MT) and alpha-2 macroglobulin (alpha-2M) is crucial for the immune efficiency during ageing and in age-related diseases, because these proteins may be involved in antagonistic pleiotropic effects. Indeed, the presence of chronic inflammation during ageing, generally, induces overexpression of these proteins that, due to their original biological function in fighting stressor agents, continuously sequester intracellular zinc. As a consequence, a low zinc ion availability may appear in aged organisms leading to impairments of the immune response at thymic and extrathymic levels with the risk of the appearance of age-related diseases. Therefore, MT and alpha-2M turn from protective in "young-adult age" to harmful agents in "ageing" following the basic assumption of an evolutionary theory of ageing, named the "antagonistic pleiotropy", which suggests that a trade off between early beneficial effects and late negative outcomes can occur at a genetic and molecular level. On the other hand, some polymorphisms of MT (MT2A) and alpha-2M have been associated with atherosclerosis or Alzheimer disease, respectively. Physiological zinc supplementation in elderly restores the thymic endocrine activity and innate immune response (NK cell cytotoxicity) and increases the survival rate in old mice. Therefore, zinc supplementation is useful to achieve health longevity because these zinc-binding proteins may regain their original protective task against oxidative damage with, thus, a beneficial impact on immune response.

Mineral bioavailability and metabolism determined by using stable isotope tracers1

Definitive data on mineral bioavailability in humans and animals can be obtained by using isotopic tracers. The use of stable isotope tracers to study important issues in mineral nutrition has expanded rapidly in the past two decades, particularly in human nutrition studies. Stable isotopes have a number of advantages over radioisotopes. There is no exposure to radiation with stable isotopes, and some minerals have no radioisotope that can be used satisfactorily as a tracer. Multiple stable isotopes of one mineral and isotopes of multiple minerals can be administered simultaneously or sequentially. The analytical methods of choice for stable isotopes are thermal ionization mass spectrometry and inductively coupled plasma mass spectrometry (ICPMS). Thermal ionization mass spectrometry offers the greatest precision and accuracy, but it is slower, more labor intensive, and more costly than ICPMS. Bioavailability data are critical to establishing reliable dietary mineral requirements and recommendations. Combined with a computer program for compartmental modeling, mineral kinetics can be studied, including mineral turnover, pool sizes, and transfer rates between compartments. Our laboratory conducts studies using stable isotopes of Zn, Cu, Fe, Ca, Mg, and Mo. We have studied the effect of the amount of dietary intake of minerals on bioavailability and use, pregnancy and aging, and interactions among minerals. The research resulted in establishing new dietary recommendations for Cu and Mo and developing compartmental models for these minerals. Although stable isotopes have been used more extensively to date in humans than in animals, the techniques applied to humans can be used to study a number of issues important to optimizing feeding strategies for animal production.

Dietary inulin intake and age can affect intestinal absorption of zinc and copper in rats

Nondigestible inulin-type fructan intake can stimulate intestinal mineral absorption in both humans and animals. However, this stimulatory effect may depend on experimental conditions such as the duration of the experience, mineral levels in the diet, and the animal's physiological status. The aim of this study was to determine the effect of inulin intake on Zn and Cu absorption in rats at different ages. Male Wistar rats (n = 80) of 4 different ages (2,5, 10, and 20 mo) were randomly assigned to a control group or a group administered 3.75% inulin in their diet for 4 d followed by 7.5% inulin for 26 d. Absorption of Zn67 and Cu65 was determined on d 21 of the experiment by fecal monitoring using Zn67 and Cu65 isotopes. Zn and Cu status was also assessed. Absorption of Zn67 and Cu65 was significantly lower in 11- and 21-mo-old rats than in 3- and 6 mo-old-rats. Moreover, inulin intake significantly increased Zn67 and Cu65 absorption. In conclusion, age and dietary inulin intake can significantly affect intestinal absorption of zinc and copper in rats. Further studies are required to explore this effect over longer periods of inulin intake and to test the effects of inulin in humans.

The effect of aging on intestinal absorption and status of calcium, magnesium, zinc, and copper in rats: a stable isotope study

Many investigators have reported changes in mineral status with age but conflicting observations were done concerning mineral absorption. This study was conducted to clarify the effect of aging on intestinal absorption and status of minerals, using a stable isotope approach. To do so, 40 rats of different ages: 9, 22, 44, and 88 weeks were fed with a semi-purified diet for a total of 30 days. At the beginning of the 4th week, the rats received a stable isotope solution containing (44)Ca, (25)Mg, (67)Zn, and (65)Cu. Individual feces and urine were then collected during 4 consecutive days in order to measure stable isotopes by inductively coupled plasma/mass spectrometry (ICP/MS) and blood and tissues were sampled for mineral status determination. Intestinal absorption of (44)Ca and (67)Zn considerably decreased with age, whereas intestinal (25)Mg absorption decreased only moderately and intestinal (65)Cu absorption was unaffected. Plasma and bone calcium (Ca) were not modified with age whereas urinary Ca excretion considerably increased. Plasma and erythrocyte magnesium (Mg) levels were unaffected with age whereas urinary Mg excretion and Mg bone level decreased. Plasma zinc (Zn) level decreased and bone Zn level increased with age whereas red blood cell and liver Zn level and urinary Zn excretion remained unchanged. Plasma Cu level increased with age whereas liver and bone Cu levels and urinary Cu excretion remained unchanged. These results show that the effect of aging on the intestinal mineral absorption and status differ largely according to the mineral considered. Further studies are required under different nutritional conditions to explore the underlying mechanisms during aging and to adjust a better nutrition of the elderly.

Zinc Supplementation Reduces Fractional Zinc Absorption in Young and Elderly Korean Women

BACKGROUND

Adjustments in zinc losses and absorption are thought to maintain zinc homeostasis with changes in intake, but the capacity to make these adjustments appears to be affected by aging. Zinc status of the individual may also influence adjustments in fractional zinc absorption.

OBJECTIVE

The purpose of this study was to compare the effects of changes in zinc status due to zinc supplementation on fractional zinc absorption in young and elderly Korean women.

DESIGN

Zinc status and absorption were measured initially in 15 young (20-24 yr) and 15 elderly women (64-75 yr) confined to a metabolic unit and consuming a typical Korean diet. Upon discharge from the unit the women were supplemented with 22 mg zinc/d for 28 days. On d 20, the women returned to the unit for measurement of zinc status and absorption. Fractional zinc absorption (FZA) was estimated from the same typical Korean breakfast at both time points using the dual isotopic tracer method. Zinc stable isotopic ratios were measured in urine samples collected for 3 days following isotope administration.

RESULTS

Plasma and urinary zinc concentrations increased significantly with zinc supplementation in the young but not the elderly women. FZA decreased following zinc supplementation in the young women from 22 to 8% (p < 0.0001) and in the elderly women from 19 to 10% (p < 0.0001). The decline in young women was greater than that in elderly women (p < 0.05).

CONCLUSIONS

Both young and elderly women reduced their efficiency of zinc absorption with zinc supplementation. But, plasma and urinary zinc concentrations did not increase in the elderly following zinc supplementation suggesting that age altered the use of the additional zinc.

Investigation of lymphocyte gene expression for use as biomarkers for zinc status in humans

A bioassay for zinc status in humans has been sought due to the importance of zinc, an essential trace metal, for many divergent functions in the human body; however, a sensitive bioassay for zinc status in humans is lacking. To address this issue, we established gene expression profiles of human lymphoblastoid cells treated with 0 or 30 micro mol/L ZnSO(4) using microarray technology. A limited number of genes were responsive to 30 micro mol/L zinc based on the analysis of Affymetrix human genome U133A GeneChips. We also examined the gene expression patterns of zinc transporters in human lymphoblastoid cells using quantitative RT-PCR analysis. ZNT1 was upregulated in lymphoblastoid cells, whereas ZIP1 was downregulated in response to the increased zinc concentrations in the culture media. To evaluate the potential applications of using both zinc transporter genes as biomarkers of zinc status, we measured the expression levels of ZIP1 and ZNT1 in the peripheral leukocytes collected from 2 different age groups of Korean women. After administration of a zinc supplement (22 mg zinc gluconate/d for 27 d), ZIP1 expression decreased by 17% (P < 0.01) and 21% (P < 0.05) in the peripheral leukocytes collected from 15 young (20-25 y) and 10 elderly (64-75 y) subjects, respectively. ZNT1 expression was not affected by taking the zinc supplement. These data suggest a potential application of ZIP1 as a biomarker of zinc status in humans.

Metallothionein (I+II) confers, via c-myc, immune plasticity in oldest mice: model of partial hepatectomy/liver regeneration

Because of its similarity to ageing in impaired immune efficiency 48 h after surgical procedures on young partially hepatectomised mice, partial hepatectomy/liver regeneration (pHx) provides a good model for the study of inflammation in ageing. In old age, high metallothionein (I+II) (MT) sequesters a substantial number of intracellular zinc ions consequently leading to low zinc ion bioavailability for an adequate immune response. Corticosterone and IL-6 affect MTmRNA induction in inflammation and after pHx against oxidative damage. The aim of this study was to investigate the role played by MT in conferring immune plasticity in ageing and in very old age using the pHx model. 48 h after their partial hepatectomy, the crude zinc balance was negative in young, old and very old mice coupled with increased MT, corticosterone, sIL-6R and IL-6. Concomitantly, Natural Killer (NK) cell activity and IL-2 production decreased. Complete restoration of the nutritional–endocrine–immune parameters occurred 15 days from the surgical procedures in young and very old mice, but not in old or transgenic mice overexpressing MT. A significant positive or inverse correlation among nutritional–endocrine–immune parameters exists in young and very old mice, but not in old mice during liver regeneration. Since MT also affects c-myc, the gene expression of c-myc declines from 48 h to days 7 and 15 after pHx in young and very old mice, but remains constantly high in old pHx mice for the same days. This circumstance leads to the appearance of tumours in the long run in old pHx mice and survival times that are shorter than old sham controls. Because complete remodelling also occurs in IL-6 and in sIL-6R in very old mice during liver regeneration, the pre-existing inflammation is not detrimental in very old age. As such, very old mice are still responsive to large inflammation, such as pHx, thanks to correct MT homeostasis. Correct MT homeostasis, via c-myc, is therefore pivotal in both suitable liver regeneration and in conferring immune plasticity with subsequent successful ageing. High MT plays an extremely harmful role in ageing: on one hand it lowers zinc ion bioavailability levels required for immune efficiency and on the other hand it increases c-myc expression. The combination of immune depression and enhanced c-myc, via high MT, may trigger the appearance of age-related degenerative diseases.

Is there a potential therapeutic value of copper and zinc for osteoporosis?

Osteoporosis is almost universal in very old age, and is a major cause of morbidity and mortality in the elderly of both sexes. Bone is lost at a rate of 0.2-0.5 %/year in both men and women after the age of 40-45 years. The causes of age-related changes in bone mass are multifactorial and include genetic predisposition, nutritional factors, endocrine changes, habitual exercise levels and body weight. Bone loss is accelerated to 2-5 % year immediately before and for up to 10 years post-menopause (Heaney, 1986). In women hormone-replacement therapy is effective in reducing the rate of bone loss caused by this peri-menopausal decrease in hormone levels (Smith & Studd, 1993); however, in men and older women (>10 years post-menopause) nutrition plays a key role in the rate of bone loss. One factor contributing to bone loss in the elderly may be a subclinical Zn and/or Cu deficiency, due to a reduced dietary intake of micronutrients and reduced absorption (Thomson & Keelan, 1986). Zn and Cu are essential cofactors for enzymes involved in the synthesis of various bone matrix constituents. Paradoxically, Ca supplementation may accentuate the problem of reduced Zn and Cu levels by impairing the absorption of simultaneously-ingested Zn and the retention of Cu (Snedeker et al. 1982; Grekas et al. 1988). The present paper will review the current literature on the potential benefits of Cu and Zn supplementation in reducing bone loss, and present new information on the effect of Ca supplementation on Zn and Cu status in post-menopausal women with osteoporosis.

Assessment of intestinal absorption of trace metals in humans by means of stable isotopes

This study is aimed to demonstrate the feasibility of stable isotopes for the assessment of reliable data on fractional intestinal absorption of trace metals in healthy humans. Among the various methods available, the double isotope technique, i.e. one isotope given orally together with the test substance to be investigated and another isotope injected intravenously to correct for retention and endogenous excretion of the particular trace metal, provides quantitative figures of intestinal absorption at reasonable expenses with regard to costs for materials and number of samples to be evaluated. The trace metals exemplarily included in this study, i.e. iron, cobalt and molybdenum show diverging relations between absorbed fractions and amounts administered which are indicative for different regulatory mechanisms of their body content. Food ligands influence the fractional absorption significantly so that the uptake from a composite meal cannot be derived from results on uptake from particular foodstuffs. Therefore, validated data on the behaviour of intestinal absorption will significantly contribute to a better understanding of human trace metal metabolism.

Interrelationships of key variables of human zinc homeostasis: relevance to dietary zinc requirements

Currently, estimates of human zinc requirements depend primarily on a factorial approach. The availability of tracer techniques employing zinc stable isotopes has facilitated the acquisition of data on major variables of zinc homeostasis in addition to those that can be measured with careful metabolic balance techniques. These data have promising potential to facilitate and improve the factorial approach. The thesis proposed in this paper is that realistic estimations of dietary zinc requirements by a factorial approach require attention to the dynamic interrelationships between major variables of zinc homeostasis. This applies especially to the positive relationship between endogenous fecal zinc and total absorbed zinc, which is the essential starting point in estimating physiologic and, from there, dietary requirements.

A zinc-sensing receptor triggers the release of intracellular Ca2+ and regulates ion transport

Changes in extracellular zinc concentration participate in modulating fundamental cellular processes such as proliferation, secretion, and ion transport in a mechanism that is not well understood. Here, we show that a micromolar concentration of extracellular zinc triggers a massive release of calcium from thapsigargin-sensitive intracellular pools in the colonocytic cell line HT29. Calcium release was blocked by a phospholipase-C inhibitor, indicating that formation of inositol 1,4,5-triphosphate is required for zinc-dependent calcium release. Zinc influx was not observed, indicating that extracellular zinc triggered the release. The Ca(i)2+ release was zinc specific and could not be triggered by other heavy metals. Furthermore, zinc failed to activate the Ca(2+)-sensing receptor heterologously expressed in HEK293 cells. The zinc-induced Ca(i)2+ rise stimulated the activity of the Na(+)/H(+) exchanger in HT29 cells. Our results indicate that a previously uncharacterized extracellular, G protein-coupled, Zn(2+)-sensing receptor is functional in colonocytes. Because Ca(i)2+ rise is known to regulate key cellular and signal-transduction processes, the zinc-sensing receptor may provide the missing link between extracellular zinc concentration changes and the regulation of cellular processes.