Effect of improved zinc status on T helper cell activation and TH1/TH2 ratio in healthy elderly individuals

Ca2+ signals are essential for T-cell proliferation, while Zn2+ signals are necessary for T helper cell 1 differentiation

The regulation of T-cell fate is crucial for the balance between infection control and tolerance. Calcium (Ca2+) and zinc (Zn2+) signals are both induced after T-cell stimulation, but their specific roles in the fate of activation and differentiation remain to be elucidated. Are Zn2+- and Ca2+ signals responsible for different aspects in T-cell activation and differentiation and do they act in concert or in opposition? It is crucial to understand the interplay of the intracellular signals to influence the fate of T cells in diseases with undesirable T-cell activities or in Zn2+-deficient patients. Human peripheral blood mononuclear cells were stimulated with the Zn2+ ionophore pyrithione and thapsigargin, an inhibitor of the sarcoplasmic/endoplasmic reticulum Ca2+ ATPase (SERCA). Intracellular Zn2+ and Ca2+ signals were monitored by flow cytometry and ELISA, quantitative PCR and western blot were used to evaluate T-cell differentiation and the underlying molecular mechanism. We found that Zn2+ signals upregulated the early T-cell activation marker CD69, interferon regulatory factor 1 (IRF-1), and Krüppel-like factor 10 (KLF-10) expression, which are important for T helper cell (Th) 1 differentiation. Ca2+ signals, on the other hand, increased T-bet and Forkhead box P3 (FoxP3) expression and interleukin (IL)-2 release. Most interestingly, the combination of Zn2+ and Ca2+ signals was indispensable to induce interferon (IFN)-γ expression and increased the surface expression of CD69 by several-fold. These results highlight the importance of the parallel occurrence of Ca2+ and Zn2+ signals. Both signals act in concert and are required for the differentiation into Th1 cells, for the stabilization of regulatory T cells, and induces T-cell activation by several-fold. This provides further insight into the impaired immune functions of patients with zinc deficiency.

Zinc Deficiency and Zinc Supplementation in Allergic Diseases

In recent decades, it has become clear that allergic diseases are on the rise in both Western and developing countries. The exact reason for the increase in prevalence has not been conclusively clarified yet. Multidimensional approaches are suspected in which diet and nutrition seem to play a particularly important role. Allergic diseases are characterized by a hyper-reactive immune system to usually harmless allergens, leading to chronic inflammatory diseases comprising respiratory diseases like asthma and allergic rhinitis (AR), allergic skin diseases like atopic dermatitis (AD), and food allergies. There is evidence that diet can have a positive or negative influence on both the development and severity of allergic diseases. In particular, the intake of the essential trace element zinc plays a very important role in modulating the immune response, which was first demonstrated around 60 years ago. The most prevalent type I allergies are mainly based on altered immunoglobulin (Ig)E and T helper (Th)2 cytokine production, leading to type 2 inflammation. This immune status can also be observed during zinc deficiency and can be positively influenced by zinc supplementation. The underlying immunological mechanisms are very complex and multidimensional. Since zinc supplements vary in dose and bioavailability, and clinical trials often differ in design and structure, different results can be observed. Therefore, different results are not surprising. However, the current literature suggests a link between zinc deficiency and the development of allergies, and shows positive effects of zinc supplementation on modulating the immune system and reducing allergic symptoms, which are discussed in more detail in this review.

Association between dietary zinc intake and asthma in overweight or obese children and adolescents: A cross-sectional analysis of NHANES

Background

Asthma, characterized by recurrent wheezing, breathlessness, chest tightness, and coughing, is a major health concern among children and adolescents worldwide, currently affecting more than 5 million children. The increasing prevalence of obesity and overweight among the pediatric population has made the issue of childhood respiratory health more complex. Compared with children of healthy weight, the risk of asthma is higher in overweight and obese children. Zinc, a nutrient that regulates the oxidant-antioxidant balance, has been studied for its potential protective effects against asthma in adults and children. However, the results are controversial, with some studies reporting a beneficial effect and others showing no effect. Therefore, our objective was to assess the correlation between zinc intake from diet and asthma occurrence among children and adolescents who are overweight or obese.

Methods

The National Health and Nutrition Examination Survey (NHANES) (2011-2020) provided data on individuals aged ≤20 who were overweight or obese, had asthma, and consumed zinc in their diet. The association between dietary zinc and asthma was evaluated using a variety of statistical methods, including multivariate logistic regression, restricted cubic spline analysis, and subgroup analysis.

Results

A total of 4597 pediatrics and adolescents were enrolled, with 20.9% (963/4597) suffering from asthma. After adjusting for all covariates in the multivariate logistic regression, compared with the lowest zinc intake group Q1(≤5.68 mg/day), the adjusted OR values for zinc intake and asthma in Q2 (5.69-8.36 mg/day), Q3 (8.37-11.95 mg/day), and Q4 (≥11.96 mg/day) were 0.78 (95% CI: 0.62-0.98, p = 0.03), 0.76 (95% CI: 0.6∼0.98, p = 0.032), 0.71 (95% CI: 0.53∼0.95, p = 0.022), respectively. Stratified analysis showed no interactive role for dietary zinc intake and asthma in overweight or obese children and adolescents.

Conclusions

Dietary zinc intake is inversely associated with asthma in overweight or obese children and adolescents.

Zinc Ionophore Pyrithione Mimics CD28 Costimulatory Signal in CD3 Activated T Cells

Zinc is an essential trace element that plays a crucial role in T cell immunity. During T cell activation, zinc is not only structurally important, but zinc signals can also act as a second messenger. This research investigates zinc signals in T cell activation and their function in T helper cell 1 differentiation. For this purpose, peripheral blood mononuclear cells were activated via the T cell receptor-CD3 complex, and via CD28 as a costimulatory signal. Fast and long-term changes in intracellular zinc and calcium were monitored by flow cytometry. Further, interferon (IFN)-γ was analyzed to investigate the differentiation into T helper 1 cells. We show that fast zinc fluxes are induced via CD3. Also, the intracellular zinc concentration dramatically increases 72 h after anti-CD3 and anti-CD28 stimulation, which goes along with the high release of IFN-γ. Interestingly, we found that zinc signals can function as a costimulatory signal for T helper cell 1 differentiation when T cells are activated only via CD3. These results demonstrate the importance of zinc signaling alongside calcium signaling in T cell differentiation.

Dietary Zn deficiency, the current situation and potential solutions

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

Short-term zinc supplementation of zinc-deficient seniors counteracts CREMα - mediated IL-2 suppression

Background

Aging is accompanied by a dramatic decline in the interleukin (IL)-2 production capacity of human immune cells, thus making seniors more susceptible to a variety of age-related diseases. A common cause of impaired cytokine production in advanced age is a deficiency of the essential micronutrient zinc. Nevertheless, the molecular mechanisms underlying a zinc deficiency-induced decrease in IL-2 production have not yet been satisfactorily elucidated. Recent animal and in vitro data suggested that the transcription factor cAMP-responsive element modulator (CREM) \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\alpha$$\end{document}α plays a critical role in T cells´ disturbed IL-2 production in suboptimal zinc conditions. However, its role in the human aging process and the possibility of influencing this detrimental process by short-term zinc supplementation have not yet been evaluated.

Results

Comparing peripheral lymphocytes of 23 young and 31 elderly subjects with either high, intermediate, or deficient zinc status, we observed zinc-dependent regulation of the IL-2 production mediated by the transcription factor CREM \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\alpha$$\end{document}α. For the first time in humans, we report a mutual relationship between low zinc levels, high CREM \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\alpha$$\end{document}α expression, subsequent impaired IL-2 production, and vice versa. Remarkably, an average of only 6 days of in vivo zinc supplementation to zinc-deficient seniors was sufficient to rapidly improve zinc status, reverse CREM \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\alpha$$\end{document}α overexpression, and counteract subsequent low IL-2 production rates.

Conclusions

Our ex vivo and in vivo data identify zinc deficiency-mediated CREM \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\alpha$$\end{document}α overexpression as a key cellular mechanism underlying impaired IL-2 production in the elderly and point toward the use of zinc as a rapidly immune-enhancing add-on nutraceutical in geriatric therapy.

Graphical abstract

During the aging process, there is a progressive decrease in zinc status, which in turn leads to overexpression of the transcription factor CREM\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\mathrm{\alpha }$$\end{document}α in peripheral lymphocytes. CREMα is a negative regulator of the IL-2 gene, the overexpression of which dramatically limits adequate IL-2 production. This deleterious mechanism can be counteracted by short-term oral zinc administration, which can adjust IL-2 production in old, zinc-deficient individuals to a level similar to that of young adults.

Perspective: Role of Micronutrients and Omega-3 Long-Chain Polyunsaturated Fatty Acids for Immune Outcomes of Relevance to Infections in Older Adults-A Narrative Review and Call for Action

The immune system is weakened by advancing age, often referred to as immunosenescence, increasing the vulnerability to, and frequently the severity of, infectious diseases in older people. This has become very apparent in the current coronavirus disease 2019 (COVID-19) pandemic for which older people are at higher risk of severe outcomes, even those who are fully vaccinated. Aging affects both the innate and adaptive immune systems and is characterized by an imbalanced inflammatory response. Increasing evidence shows that optimal status of nutrients such as vitamins C, D, and E and selenium and zinc as well as the omega-3 (n-3) fatty acids DHA and EPA can help compensate for these age-related changes. While inadequate intakes of these nutrients are widespread in the general population, this is often more pronounced in older people. Maintaining adequate intakes is a challenge for them due to a range of factors such as physical, physiological, and cognitive changes; altered absorption; and the presence of noncommunicable diseases. While nutritional requirements are ideally covered by a balanced diet, this can be difficult to achieve, particularly for older people. Fortified foods and nutritional complements are effective in achieving adequate micronutrient intakes and should be considered as a safe and cost-effective means for older people to improve their nutritional status and hence support their defense against infections. Complementing the diet with a combination of micronutrients, particularly those playing a key role in the immune system such as vitamins C, D, and E and selenium and zinc as well as DHA and EPA, is recommended for older people. Optimal nutrition to support the immune system in older people will remain essential, particularly in the face of the current COVID-19 pandemic and, thus, developing strategies to ensure adequate nutrition for the growing number of older adults will be an important and cost-effective investment in the future.

Impact of zinc on DNA integrity and age-related inflammation

Dr. Bruce Ames was a pioneer in understanding the role of oxidative stress and DNA damage, and in the 1990s began to make connections between micronutrient deficiencies and DNA damage. Zinc is an essential micronutrient for human health and a key component for the function of numerous cellular processes. In particular, zinc plays a critical role in cellular antioxidant defense, the maintenance of DNA integrity and is also essential for the normal development and function of the immune system. This review highlights the work helping connect zinc deficiency to oxidative stress, susceptibility to DNA damage and chronic inflammation that was initiated while working with Dr. Ames. This review outlines the body of work in this area, from cells to humans. The article also reviews the unique challenges of maintaining zinc status as we age and the interplay between zinc deficiency and age-related inflammation and immune dysfunction. Several micronutrient deficiencies, including zinc deficiency, can drastically affect the risk of many chronic diseases and underscores the importance of adequate nutrition for healthy aging.

Mineral Micronutrients in Asthma

Asthma represents one of the most common medical issues in the modern world. It is a chronic inflammatory disease characterized by persistent inflammation of the airways and disturbances in redox status, leading to hyperresponsiveness of bronchi and airway obstruction. Apart from classical risk factors such as air pollution, family history, allergies, or obesity, disturbances of the levels of micronutrients lead to impairments in the defense mechanisms of the affected organism against oxidative stress and proinflammatory stimuli. In the present review, the impact of micronutrients on the prevalence, severity, and possible risk factors of asthma is discussed. Although the influence of classical micronutrients such as selenium, copper, or zinc are well known, the effects of those such as iodine or manganese are only rarely mentioned. As a consequence, the aim of this paper is to demonstrate how disturbances in the levels of micronutrients and their supplementation might affect the course of asthma.

The Effects of Zinc Supplementation on C-Reactive Protein and Inflammatory Cytokines: A Meta-Analysis and Systematical Review

Zinc is known for anti-inflammatory and antioxidant roles. In this meta-analysis, we aim to evaluate the impact of zinc supplementation on inflammatory markers, acute-phase reactants, and serum zinc level during inflammatory and infectious diseases. PubMed, Scopus, and Web of Science databases were screened systematically with the terms "zinc supplementation" AND "CRP" OR "IL-1β" OR "IL-2" OR "IL-6" OR "IL-10" OR "IL-12" OR "TNF-α" OR "TGF-β" OR "IFN-γ" OR "WBC (clinical trial)" OR "macrophage (clinical trial)" OR "lymphocyte (clinical trial)" OR "neutrophil (clinical trial)" OR "virus (clinical trial)" OR "antiviral (clinical trial)" for all databases. A total of 2,258 publications were screened, and 73 articles had suitable data for the meta-analysis. Serum zinc level was significantly higher in supplementation group compared with controls [P = 0.0006, mean difference: 11.35 (4.84, 17.87)] (n = 37). Zinc supplementation downregulates acute-phase reactants, especially serum C-reactive protein (CRP) in adults [P < 0.00001, mean difference: -0.75 (-0.98, -0.52)] (n = 22) and pregnant women [FEM P < 0.00001, mean difference: -1.77 (-2.53, -1.00)] (n = 3) but not in children [REM P = 0.10, mean difference: -0.85 (-1.86, 0.17)] (n = 3). In subgroups analysis of chronic inflammatory diseases, serum CRP [REM P < 0.00001, mean difference: -0.57 (-0.76, -0.38)] were significantly lower in zinc-supplemented patients compared with no intervention group. Zinc supplementation (mg/day) correlated with serum interferon-gamma (IFN-γ) level (P = 0.018, r = 1,000). In the nonsupplemented group, serum zinc correlated with serum interleukin-6 (IL-6) level (P = 0.041, r = -0.829) and serum tumor necrosis factor alpha (TNF-α) level (P = 0.063, r = 0.730). Zinc intake correlated with serum zinc (P = 0.0428, r = 0.5115) and TNF-α (P = 0.0043, r = -0.9461). This meta-analysis shows that zinc supplementation improves CRP levels in adults and pregnant women. It might have modulatory effects on cytokine secretions and blood cells in inflammatory and infectious diseases. For the first time, we investigated the effects of zinc supplementation on inflammatory cytokine.

Nutritional Modulation of Immune Function: Analysis of Evidence, Mechanisms, and Clinical Relevance

It is well-established that the nutritional deficiency or inadequacy can impair immune functions. Growing evidence suggests that for certain nutrients increased intake above currently recommended levels may help optimize immune functions including improving defense function and thus resistance to infection, while maintaining tolerance. This review will examine the data representing the research on prominent intervention agents n-3 polyunsaturated fatty acids (PUFA), micronutrients (zinc, vitamins D and E), and functional foods including probiotics and tea components for their immunological effects, working mechanisms, and clinical relevance. Many of these nutritive and non-nutritive food components are related in their functions to maintain or improve immune function including inhibition of pro-inflammatory mediators, promotion of anti-inflammatory functions, modulation of cell-mediated immunity, alteration of antigen-presenting cell functions, and communication between the innate and adaptive immune systems. Both animal and human studies present promising findings suggesting a clinical benefit of vitamin D, n-3 PUFA, and green tea catechin EGCG in autoimmune and inflammatory disorders, and vitamin D, vitamin E, zinc, and probiotics in reduction of infection. However, many studies report divergent and discrepant results/conclusions due to various factors. Chief among them, and thus call for attention, includes more standardized trial designs, better characterized populations, greater consideration for the intervention doses used, and more meaningful outcome measurements chosen.

Zinc supplementation can reduce accumulation of cadmium in aged metallothionein transgenic mice

Epidemiologic studies suggest that exposure to Cd is related to a multitude of age-related diseases. There is evidence that Cd toxicity emerges from an interference with Zn metabolism as they compete for the same binding sites of ligands. The most responsive proteins to Cd exposure are the metal-binding proteins termed metallothioneins (MTs), which display a much greater affinity for Cd than for Zn. Most studies have considered the effect of Zn on the accumulation of exogenous Cd and tissue damage, whereas observational studies have addressed the association between Zn intake and Cd levels in body fluids. However, it has not been addressed whether supplemental Zn can lower Cd levels in organs of healthy aged animals without affecting Cu stores, a question more pertinent to human aging. We therefore aimed to investigate the effect of Zn supplementation on Cd levels in liver and kidney of aged MT transgenic mice (MT1-tg) overexpressing MT1 at levels more comparable to those observed in humans than non-transgenic mice. We found a >30% reduction of kidney and liver Cd levels in Zn supplemented MT1-tg mice compared to non-supplemented controls, independently of the dose of Zn, without a significant reduction of Cu. Our data support the idea of a causal and inverse relationship between Zn intake and Cd content in organs of aged MT1-tg mice as suggested by observational studies in humans. Our work provides the rationale for interventional studies to address the effects of Zn supplementation on Cd burden in elderly people.

The immunomodulatory role of zinc in asthmatic patients

BACKGROUND

Zinc deficiency may play an important role in the development of atopic asthma.

THE AIM OF THE WORK

To assess serum zinc levels in adult atopic, non-atopic asthmatic patients, and in healthy controls and to investigate its modulatory effect on production of interferon gamma (IFN-γ) and interleukin-10 (IL-10) by peripheral blood mononuclear cells (PBMCs) in vitro.

METHODS

Sixty asthmatics and 30 apparently healthy volunteers were included in this study. All patients were subjected to history taking, clinical examination, pulmonary function tests, skin prick test (SPT), serum zinc assessment by a colorimetric method as well as serum total IgE measurement by Enzyme-linked immunosorbent assay (ELISA). PBMCs were activated in vitro in the presence and absence of zinc, and then cell culture supernatants were analyzed for IFN-γ and IL-10 by ELISA.

RESULTS

Serum zinc levels were significantly lower in atopic asthmatics than non-atopic asthmatics and healthy controls. In atopic asthmatics, highly significant correlations were found between zinc levels and total Ig E levels as well as FEV1. In culture, zinc triggers IFN-γ and inhibits IL-10 production by PBMCs, in atopic asthmatics. In non atopic asthmatics and healthy controls, IFN-γ and IL-10 were slightly affected by zinc supplementation in culture.

CONCLUSION

Serum zinc levels affect asthma phenotypes. Atopic asthmatics might benefit from zinc supplements.

Nutritional modulation of age-related changes in the immune system and risk of infection

The immune system undergoes some adverse alterations during aging, many of which have been implicated in the increased morbidity and mortality associated with infection in the elderly. In addition to intrinsic changes to the immune system with aging, the elderly are more likely to have poor nutritional status, which further impacts the already impaired immune function. Although the elderly often have low zinc serum levels, several manifestations commonly observed during zinc deficiency are similar to the changes in immune function with aging. In the case of vitamin E, although its deficiency is rare, the intake above recommended levels is shown to enhance immune functions in the elderly and to reduce the risk of acquiring upper respiratory infections in nursing home residents. Vitamin D is a critical vitamin in bone metabolism, and its deficiency is far more common, which has been linked to increased risk of infection as demonstrated in a number of observational studies including those in the elderly. In this review, we focus on zinc, vitamin E, and vitamin D, the 3 nutrients which are relatively well documented for their roles in impacting immune function and infection in the elderly, to discuss the findings in this context reported in both the observational studies and interventional clinical trials. A perspective will be provided based on the analysis of information under review.

Lower Plasma Zinc Levels in Hyperglycemic People Living with HIV in the MASH cohort

BACKGROUND

Zinc deficiency is prevalent in HIV and hyperglycemic patients. Antiretroviral therapy (ART) is a treatment to control HIV progression; however it increases the risk for hyperglycemia. The objective of this study was to assess the plasma zinc levels in hyperglycemic people living with HIV (PLWH).

METHODS

Secondary analysis was conducted on the data from the Miami Adult Studies in HIV (MASH) cohort in Florida. Patients were categorized into hyperglycemic group (fasting blood glucose ≥100 mg/dL) and normal group (<100 mg/dL).

RESULTS

Plasma zinc status and CD4 levels were lower in the hyperglycemic group, however the difference was not significant. There was a greater percentage of plasma zinc deficiency in the hyperglycemic group (69%) compared to the normoglycemic group (64%).

DISCUSSION

Although not statistically significant, related biomarkers such as plasma zinc levels and CD4 levels were lower in the hyperglycemic group. This may be due to the role zincplays in the immune system. Due to the fact that there was a higher percentage of plasma zinc deficiency in the hyperglycemic group (69%) compared to the normoglycemic group (64%), it is important to monitor and manage blood glucose levels to minimize complications. Our findings along with previous findings suggest that zinc supplementation may benefit hyperglycemic PLWH.

Implications of compromised zinc status on bone loss associated with chronic inflammation in C57BL/6 mice

Compromised zinc status and chronic inflammation are independent factors that can contribute to bone loss. However, zinc’s role in regulating lymphoid and myeloid cell populations, combined with the interplay between the immune and skeletal systems raises the question as to the extent to which a low-grade inflammatory challenge in the context of marginal zinc deficiency would exacerbate bone loss. To address this question, young adult C57BL/6 male mice (n=32) were used in a 2×2 factorial design with dietary zinc (adequate or 35 ppm vs inadequate or −Zn =5 ppm) and lipopolysaccharide (LPS, 0 or 0.1 mg/kg body weight). Mice were fed their respective diets for 10 weeks. On the 6th week, mice had a slow release pellet implanted to induce a low-grade inflammation for the final 4 weeks of the study. −Zn induced a decrease in total white cell counts and peripheral lymphocytes, whereas LPS increased blood monocytes. LPS significantly reduced spine bone mineral density and trabecular bone volume and number of the vertebral body compared with both zinc adequate and inadequate without LPS groups. Likewise, the most pronounced effects on bone strength occurred with LPS, however, −Zn also had negative effects on the bone von Mises stresses. LPS induced an increase in TNF-α and this response was further increased with −Zn. Although the marginal zinc deficiency altered immune function, bone loss was not exacerbated with low-grade chronic inflammation in marginally zinc-deficient young adult mice. These findings demonstrate that in young adult animals an immune challenge modestly increases the inflammatory response and worsens bone biomechanics in the context of a marginal zinc deficiency, but not to the extent that more severe adverse outcomes are observed on bone structural parameters.

Zinc homeostasis and immunosenescence

For more than 50 years, zinc is known to be an essential trace element, having a regulatory role in the immune system. Deficiency in zinc thus compromises proper immune function, like it is observed in the elderly population. Here mild zinc deficiency is a common condition, documented by a decline of serum or plasma zinc levels with age. This leads to a dysregulation mainly in the adaptive immunity that can result in an increased production of pro-inflammatory cytokines, known as a status called inflamm-aging. T cell activation as well as polarization of T helper (Th) cells into their different subpopulations (Th1, Th2, Th17, regulatory T cells (Treg)) is highly influenced by zinc homeostasis. In the elderly a shift of the Th cell balance towards Th2 response is observed, a non-specific pre-activation of T cells is displayed, as well as a decreased response to vaccination is seen. Moreover, an impaired function of innate immune cells indicate a predominance of zinc deficiency in the elderly that may contribute to immunosenescence. This review summarizes current findings about zinc deficiency and supplementation in elderly individuals.

Zinc signals and immune function

For more than 50 years, it has been known that zinc deficiency compromises immune function. During this time, knowledge about the biochemistry of zinc has continued to grow, but only recent years have provided in-depth molecular insights into the multiple aspects of zinc as a regulator of immunity. A network based on ZnT and ZIP proteins for transport and metallothionein for storage tightly regulates zinc availability, and virtually all aspects of innate and adaptive immunity are affected by zinc. In vivo, zinc deficiency alters the number and function of neutrophil granulocytes, monocytes, natural killer (NK)-, T-, and B-cells. T cell functions and balance between the different subsets are particularly susceptible to changes in zinc status. This article focuses in particular on the main mechanisms by which zinc ions exert essential functions in the immune system. On the one hand, this includes tightly protein bound zinc ions serving catalytic or structural functions in a multitude of different proteins, in particular enzymes and transcription factors. On the other hand, increasing evidence arises for a regulatory role of free zinc ions in signal transduction, especially in cells of the immune system. Identification of several molecular targets, including phosphatases, phosphodiesterases, caspases, and kinases suggest that zinc ions are a second messenger regulating signal transduction in various kinds of immune cells.

Nutrition, diet and immunosenescence

Ageing is characterized by immunosenescence and the progressive decline in immunity in association with an increased frequency of infections and chronic disease. This complex process affects both the innate and adaptive immune systems with a progressive decline in most immune cell populations and defects in activation resulting in loss of function. Although host genetics and environmental factors, such as stress, exercise and diet can impact on the onset or course of immunosenescence, the mechanisms involved are largely unknown. This review focusses on identifying the most significant aspects of immunosenescence and on the evidence that nutritional intervention might delay this process, and consequently improve the quality of life of the elderly.

Zinc: dietary intake and impact of supplementation on immune function in elderly

The diet in the elderly does not provide a sufficient level of nutrients needed to maintain an adequate healthy status leading to micronutrient deficiencies and impaired immune response with subsequent development of degenerative diseases. Nutrient "zinc" is a relevant micronutrient involved in maintaining a good integrity of many body homeostatic mechanisms, including immune efficiency, owing to its requirement for the biological activity of many enzymes, proteins and for cellular proliferation and genomic stability. Old people aged 60-65 years and older have zinc intakes below 50% of the recommended daily allowance on a given day. Many causes can be involved: among them, altered intestinal absorption, inadequate mastication, psychosocial factors, drugs interactions, altered subcellular processes (zinc transporters (Zip and ZnT family), metallothioneins, divalent metal transporter-1). Zinc supplementation may remodel the immune alterations in elderly leading to healthy ageing. Several zinc trials have been carried out with contradictory data, perhaps due to incorrect choice of an effective zinc supplementation in old subjects showing subsequent zinc toxic effects on immunity. Old subjects with specific IL-6 polymorphism (GG allele carriers; named C-) are more prone for zinc supplementation than the entire old population, in whom correct dietary habits with foods containing zinc (Mediterranean diet) may be sufficient in restoring zinc deficiency and impaired immune response. We summarise the main causes of low zinc dietary intake in elderly reporting an update on the impact of zinc supplementation upon the immune response also on the basis of individual IL-6 polymorphism.

Leptin and zinc relation: In regulation of food intake and immunity

Leptin is synthesized and released by the adipose tissue. Leptin, which carries the information about energy reserves of the body to the brain, controls food intake by acting on neuropeptide Y (NPY), which exercises a food-intake-increasing effect through relevant receptors in the hypothalamus. Zinc deficiency is claimed to result in anorexia, weight loss, poor food efficiency, and growth impairment. The fact that obese individuals have low zinc and high leptin levels suggests that there is a relation between zinc and nutrition, and consequently also between zinc and leptin. Leptin deficiency increases the predisposition to infections and this increase is associated with the impairments in the production of cytokines. Zinc has a key role in the sustenance of immune resistance against infections. Dietary zinc deficiency negatively affects CD(+) 4 cells, Th functions, and consequently, cell-mediated immunity by causing a decrease in the production of IL-2, IF-γ, and TNF-α, which are Th1 products. The relation between zinc and the concerned cytokines in particular, and the fact that leptin has a part in the immune responses mediated by these cytokines demonstrate that an interaction among cellular immunity, leptin and zinc is inevitable. An overall evaluation of the information presented above suggests that there are complex relations among food intake, leptin and zinc on one hand and among cellular immunity, leptin and zinc on the other. The aim of the present review was to draw attention to the possible relation between zinc and leptin in dietary regulation and cellular immunity.

Zinc suppressed the airway inflammation in asthmatic rats: effects of zinc on generation of eotaxin, MCP-1, IL-8, IL-4, and IFN-γ

Airway epithelium is rich in labile zinc (Zn), which may have an important protective role in the airway epithelium. The aim of this study is to investigate the effects of Zn on the airway inflammation and the generation of eotaxin, monocyte chemoattractant protein-1 (MCP-1), interleukin-8 (IL-8), interleukin-4 (IL-4), and interferon-γ (IFN-γ) in rat models of ovalbumin (OVA)-induced allergic airway inflammation. For this purpose, animal model of asthma was established by OVA challenge and zinc-deficient and zinc-supplemented diets were given. Thirty-two Sprague-Dawley rats were divided into four groups: zinc-deficient diet with OVA treatment group, zinc-supplemented diet with OVA treatment group, zinc-normal diet with OVA treatment group, and zinc-normal diet with saline treatment group. Twenty-four hours after asthma was induced, lung histomorphological changes, cells in bronchoalveolar lavage fluid (BALF), contents of eotaxin, MCP-1, and IL-8 in BALF, and the expression of IFN-γ and IL-4 mRNAs were observed. Compared with the group of zinc-normal diet with OVA challenge rats, the group of zinc-deficient rats had higher numbers of eosinophils, neutrophils, and monocytes in BALF, as well as higher contents of eotaxin and MCP-1 in BALF and lower expression of lung IFN-γ mRNA. Conversely, Zn supplementation would decrease the numbers of eosinophils, neutrophils, and monocytes in BALF; suppress eotaxin and MCP-1 protein secretion; and increase lung IFN-γ mRNA expression. No significant difference was observed in IL-8 and IL-4 among OVA-challenged rats with different zinc diets. These studies suggested that Zn may be an important anti-inflammatory mediator of airway inflammation.

Zinc deficiency induces production of the proinflammatory cytokines IL-1β and TNFα in promyeloid cells via epigenetic and redox-dependent mechanisms

The deprivation of zinc, caused by malnutrition or as a consequence of aging or disease, strongly affects immune cell functions, causing higher frequency of infections. Among other effects, an increased production of reactive oxygen species (ROS) and proinflammatory cytokines has been observed in zinc-deficient patients, but the underlying mechanisms were unknown. The aim of the current study was to define mechanisms explaining the increase in proinflammatory cytokine production during zinc deficiency, focusing on the role of epigenetic and redox-mediated mechanisms. Interleukin (IL)-1β and tumor necrosis factor (TNF)α production was increased in HL-60 cells under zinc deficiency. Analyses of the chromatin structure demonstrated that the elevated cytokine production was due to increased accessibilities of IL-1β and TNFα promoters in zinc-deficient cells. Moreover, the level of nicotinamide adenine dinucleotide phosphate-oxidase (NADPH) oxidase-produced ROS was elevated under zinc deficiency, subsequently leading to p38 mitogen-activated protein kinase (MAPK) phosphorylation. The increased activation of p38 MAPK appeared to be necessary for posttranscriptional processes in IL-1β and TNFα synthesis. These data demonstrate that IL-1β and TNFα expression under zinc deficiency is regulated via epigenetic and redox-mediated mechanisms. Assuming an important role of zinc in proinflammatory cytokine regulation, this should encourage research in the use of zinc supplementation for treatment of inflammatory diseases.

Explaining the variability in recommended intakes of folate, vitamin B12, iron and zinc for adults and elderly people

Objective

To signal key issues for harmonising approaches for establishing micronutrient recommendations by explaining observed variation in recommended intakes of folate, vitamin B12, Fe and Zn for adults and elderly people.

Design

We explored differences in recommended intakes of folate, vitamin B12, Fe and Zn for adults between nine reports on micronutrient recommendations. Approaches used for setting recommendations were compared as well as eminence-based decisions regarding the selection of health indicators indicating adequacy of intakes and the consulted evidence base.

Results

In nearly all reports, recommendations were based on the average nutrient requirement. Variation in recommended folate intakes (200–400 μg/d) was related to differences in the consulted evidence base, whereas variation in vitamin B12recommendations (1·4–3·0 μg/d) was due to the selection of different CV (10–20 %) and health indicators (maintenance of haematological status or basal losses). Variation in recommended Fe intakes (men 8–10 mg/d, premenopausal women 14·8–19·6 mg/d, postmenopausal women 7·5–10·0 mg/d) was explained by different assumed reference weights and bioavailability factors (10–18 %). Variation in Zn recommendations (men 7–14 mg/d, women 4·9–9·0 mg/d) was also explained by different bioavailability factors (24–48 %) as well as differences in the consulted evidence base.

Conclusions

For the harmonisation of approaches for setting recommended intakes of folate, vitamin B12, Fe and Zn across European countries, standardised methods are needed to (i) select health indicators and define adequate biomarker concentrations, (ii) make assumptions about inter-individual variation in requirements, (iii) derive bioavailability factors and (iv) collate, select, interpret and integrate evidence on requirements.

The immune system and the impact of zinc during aging

The trace element zinc is essential for the immune system, and zinc deficiency affects multiple aspects of innate and adaptive immunity. There are remarkable parallels in the immunological changes during aging and zinc deficiency, including a reduction in the activity of the thymus and thymic hormones, a shift of the T helper cell balance toward T helper type 2 cells, decreased response to vaccination, and impaired functions of innate immune cells. Many studies confirm a decline of zinc levels with age. Most of these studies do not classify the majority of elderly as zinc deficient, but even marginal zinc deprivation can affect immune function. Consequently, oral zinc supplementation demonstrates the potential to improve immunity and efficiently downregulates chronic inflammatory responses in the elderly. These data indicate that a wide prevalence of marginal zinc deficiency in elderly people may contribute to immunosenescence.

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.

Immunity, trauma and the elderly

It is believed that an uncontrolled or poorly coordinated immune reaction can be stimulated by major trauma and be responsible for the development of the multiple organ dysfunction syndrome (MODS). The elderly have a reduced ability to mount an effective immune reaction with deficiencies involving both humoral and cellular aspects of immunity that involve poor function of both the stimulatory and immuno-suppressive sides of the immune process. However, there is currently no hard evidence that the excess mortality after major trauma in the elderly is associated with an impaired or excessive immune response. It is possible that their poor resistance to infection is important and immune modulated but the dominant factor in the excess mortality in the elderly population is probably associated with their lack of physiological reserve to respond to a major physiological challenge.