Micronutrient Food Supplements in Patients with Gastro-Intestinal and Hepatic Cancers

Colorectal carcinogenesis is the second most common cause of mortality across all types of malignancies, followed by hepatic and stomach cancers. Chemotherapy and radiotherapy are key approaches to treating cancer patients, but these carry major concerns, such as a high risk of side effects, poor accessibility, and the non-selective nature of chemotherapeutics. A number of natural products have been identified as countering various forms of cancer with fewer side effects. The potential impact of vitamins and minerals on long-term health, cognition, healthy development, bone formation, and aging has been supported by experimental and epidemiological studies. Successful treatment may thus be highly influenced by the nutritional status of patients. An insufficient diet could lead to detrimental effects on immune status and tolerance to treatment, affecting the ability of chemotherapy to destroy cancerous cells. In recent decades, most cancer patients have been taking vitamins and minerals to improve standard therapy and/or to decrease the undesirable side effects of the treatment together with the underlying disease. On the other hand, taking dietary supplements during cancer therapy may affect the effectiveness of chemotherapy. Thus, micronutrients in complementary oncology must be selected appropriately and should be taken at the right time. Here, the potential impact of micronutrients on gastro-intestinal and hepatic cancers is explored and their molecular targets are laid down.

Nutritional status of micronutrients as a possible and modifiable risk factor for COVID-19: a UK perspective

Recent scientific evidence has indicated that the elderly have increased risk of COVID-19 infections, with over 70s and 80s being hardest hit - especially residents of care homes and in clinical settings, ethnic minorities, people who work indoors and those who are overweight and obese. Other potential risk factors include lack of exposure to sunlight, darker skin pigmentation, co-morbidities, poor diet, certain medications, disadvantaged social and economic status, and lifestyle factors such as smoking and excessive consumption of alcohol. A key question is to understand how and why certain groups of people are more susceptible to COVID-19, whether they have weakened immune systems and what the roles of good nutrition and specific micronutrients are in supporting immune functions. A varied and balanced diet with an abundance of fruits and vegetables and the essential nutrients like vitamin D, vitamin A, B vitamins (folate, vitamin B6 and vitamin B12), vitamin C and the minerals, Fe, Cu, Se and Zn are all known to contribute to the normal functions of the immune system. Avoidance of deficiencies and identification of suboptimal intakes of these micronutrients in targeted groups of patients and in distinct and highly sensitive populations could help to strengthen the resilience of people to the COVID-19 pandemic. It is important to highlight evidence-based public health messages, to prevent false and misleading claims about the benefits of foods and food supplements and to communicate clearly that the extent of knowledge between micronutrients and COVID-19 infection is still being explored and that no diet will prevent or cure COVID-19 infection. Frequent handwashing and social distancing will be critical to reduce transmission.

Potential roles of micronutrient deficiency and immune system dysfunction in the coronavirus disease 2019 (COVID-19) pandemic

Preliminary studies indicate that a robust immune response across different cell types is crucial in recovery from coronavirus disease 2019 (COVID-19). An enormous number of investigations point to the vital importance of various micronutrients in the interactions between the host immune system and viruses, including COVID-19. There are complex and multifaceted links among micronutrient status, the host immune response, and the virulence of pathogenic viruses. Micronutrients play a critical role in the coordinated recruitment of innate and adaptive immune responses to viral infections, particularly in the regulation of pro- and anti-inflammatory host responses. Furthermore, inadequate amounts of micronutrients not only weaken the immune system in combating viral infections, but also contribute to the emergence of more virulent strains via alterations of the genetic makeup of the viral genome. The aim of this study was to evaluate the evidence that suggests the contribution of micronutrients in the spread as well as the morbidity and mortality of COVID-19. Both the presence of micronutrient deficiencies among infected individuals and the effect of micronutrient supplementation on the immune responses and overall outcome of the disease could be of great interest when weighing the use of micronutrients in the prevention and treatment of COVID-19 infection. These investigations could be of great value in dealing with future viral epidemics.

Validation of the Micronutrient and Environmental Enteric Dysfunction Assessment Tool and evaluation of biomarker risk factors for growth faltering and vaccine failure in young Malian children

Environmental enteric dysfunction (EED) is an intestinal disorder common among children in low-resource settings and is associated with increased risk of growth stunting, cognitive deficits, and reduced oral vaccine immunogenicity. The Micronutrient and EED Assessment Tool (MEEDAT) is a multiplexed immunoassay that measures biomarkers previously associated with child growth faltering and/or oral vaccine immunogenicity: intestinal fatty acid–binding protein (I-FABP), soluble CD14 (sCD14), insulin-like growth factor 1 (IGF-1), and fibroblast growth factor 21 (FGF21). MEEDAT also measures systemic inflammation (α1-acid glycoprotein, C-reactive protein), ferritin, soluble transferrin receptor, retinol binding protein 4, thyroglobulin, and Plasmodium falciparum antigenemia (histidine-rich protein 2). The performance of MEEDAT was compared with commercially available enzyme-linked immunosorbent assays (ELISAs) using 300 specimens from Malian infant clinical trial participants. Regression methods were used to test if MEEDAT biomarkers were associated with seroconversion to meningococcal A conjugate vaccine (MenAV), yellow fever vaccine (YFV), and pentavalent rotavirus vaccine (PRV) after 28 days, or with growth faltering over 12 weeks. The Pearson correlations between the MEEDAT and ELISA results were 0.97, 0.86, 0.80, and 0.97 for serum I-FABP, sCD14, IGF-1, and FGF21, respectively. There were significant associations between I-FABP concentration and the probability of PRV IgG seroconversion and between IGF-1 concentration and the probability of YFV seroconversion. In multivariable models neither association remained significant, however there was a significant negative association between AGP concentration and YFV seroconversion. GLP-2 and sCD14 concentrations were significantly negatively associated with 12-week change in weight-for-age z-score and weight-for-height z-score in multivariable models. MEEDAT performed well in comparison to commercially-available ELISAs for the measurement of four analytes for EED and growth hormone resistance. Adoption of MEEDAT in low-resource settings could help accelerate the identification of interventions that prevent or treat child stunting and interventions that boost the immunogenicity of child vaccinations.

Environmental enteric dysfunction (EED) is an intestinal disorder common among children in low-resource settings and has been associated with increased risk of growth stunting, cognitive deficits, and reduced oral vaccine immunogenicity. A key challenge to identifying children with EED at highest risk of morbid sequelae is the lack of validated predictive biomarkers. Ongoing clinical studies are testing and validating EED biomarkers in child populations at risk for stunting, yet testing multiple biomarkers commonly requires specialized equipment, complex methods, resources, and considerable effort. The Micronutrient and EED Assessment Tool (MEEDAT) is a multiplexed immunoassay that measures biomarkers associated with child growth faltering and oral vaccine immunogenicity, and biomarkers indicative of systemic inflammation and micronutrient deficiencies. The performance of MEEDAT was well-correlated with commercial monoplex assays in specimens from children living in a low-resource setting in the present study. MEEDAT biomarkers were associated with growth outcomes and seroconversion in response to several vaccines. MEEDAT has the potential to reduce the time and cost of evaluating impact of interventions targeting EED.

The Role of Micronutrients in Alopecia Areata: A Review

Alopecia areata (AA) is a common, non-scarring form of hair loss caused by immune-mediated attack of the hair follicle. As with other immune-mediated diseases, a complex interplay between environment and genetics is thought to lead to the development of AA. Deficiency of micronutrients such as vitamins and minerals may represent a modifiable risk factor associated with development of AA. Given the role of these micronutrients in normal hair follicle development and in immune cell function, a growing number of investigations have sought to determine whether serum levels of these nutrients might differ in AA patients, and whether supplementation of these nutrients might represent a therapeutic option for AA. While current treatment often relies on invasive steroid injections or immunomodulating agents with potentially harmful side effects, therapy by micronutrient supplementation, whether as a primary modality or as adjunctive treatment, could offer a promising low-risk alternative. However, our review highlights a need for further research in this area, given that the current body of literature largely consists of small case-control studies and case reports, which preclude any definite conclusions for a role of micronutrients in AA. In this comprehensive review of the current literature, we found that serum vitamin D, zinc, and folate levels tend to be lower in patients with AA as compared to controls. Evidence is conflicting or insufficient to suggest differences in levels of iron, vitamin B12, copper, magnesium, or selenium. A small number of studies suggest that vitamin A levels may modify the disease. Though understanding of the role for micronutrients in AA is growing, definitive clinical recommendations such as routine serum level testing or therapeutic supplementation call for additional studies in larger populations and with a prospective design.

Dietary Intake of Antioxidant Vitamins and Carotenoids and Risk of Developing Active Tuberculosis in a Prospective Population-Based Cohort Study

Antioxidants may protect against oxidative stress, which is associated with tuberculosis (TB) disease. However, direct evidence for a protective association between dietary antioxidants and TB incidence in humans has been lacking. The relationship between intake of antioxidant vitamins (vitamins A, C, D, and E) and individual carotenoids (α-carotene, β-carotene, β-cryptoxanthin, lycopene, and lutein) and TB incidence was examined in the Singapore Chinese Health Study, a prospective cohort study of 63,257 adults aged 45-74 years enrolled during 1993-1998. Baseline intake of these antioxidants was estimated using a validated semiquantitative food frequency questionnaire including questions on use of dietary supplements. After an average of 16.9 years of follow-up, 1,186 incident active TB cases were identified among cohort participants. Compared with the lowest quartile, reduced risk of active TB was observed for the highest quartile of vitamin A intake (hazard ratio = 0.71, 95% confidence interval: 0.59, 0.85; P-trend < 0.01) and β-carotene intake (hazard ratio = 0.76, 95% confidence interval: 0.63, 0.91; P-trend < 0.01), regardless of smoking status. Lower TB risk was seen for vitamin C intake among current smokers only. Other vitamins and carotenoids were not associated with TB risk. These results suggest that vitamin C may reduce TB risk among current smokers by ameliorating oxidative stress, while vitamin A and β-carotene may have additional antimycobacterial properties.

Nutritional Immunity and Fungal Pathogenesis: The Struggle for Micronutrients at the Host-Pathogen Interface

All living organisms require certain micronutrients such as iron, zinc, manganese and copper for cellular function and growth. For human pathogens however, the maintenance of metal ion homeostasis is particularly challenging. This is because the mammalian host actively enforces extremes of micronutrient availability on potential microbial invaders-processes collectively termed nutritional immunity. The role of iron sequestration in controlling microbial infections is well established and, more recently, the importance of other metals including zinc, manganese and copper has been recognised. In this chapter, we explore the nutritional immune mechanisms that defend the human body against fungal infections and the strategies that these important pathogens exploit to counteract nutritional immunity and thrive in the infected host.

Transforming growth factor and intestinal inflammation: the role of nutrition

The intestinal mucosa possesses a complex epithelial barrier and a well-organized local immune system, which both efficiently protect this internal-external surface against potential microbial aggressions while guaranteeing tolerance towards harmless bacteria or antigens (oral tolerance). There is good experimental evidence that the intestinal microbiota is a main driver for the development of the mucosal immune system. Any perturbations/changes of this interaction with the intestinal microbiota or the microbial colonization process may cause health problems with short- and eventually long-term consequences, such as suspected for allergic or dysimmune disorders. Dendritic cells (DC) play a key role in the initiation of immune responses. Immune responses elicited by intestinal DC differ markedly from those initiated by spleen-derived DC: while intestinal DC induce anti-inflammatory and tolerogenic responses to harmless antigens such as derived from the resident microflora or harmless food allergens, systemic immune activation yields in a strong inflammatory TH1/TH17 reaction to the same antigens. The recent discovery how DC functions are regulated and imprinted by the microenvironment (DC conditioning) will be discussed in this review. High concentrations of retinoic acid or vitamin D metabolites, thymic stromal lymphopoietin and/or transforming growth factor-β (TGF-β) activate signaling programs in DC that yield in priming of regulatory and anti-inflammatory T cell responses. TGF-β is one of the key factors implicated in intestinal immune regulation; it is produced by a large variety of cells in the intestinal mucosa, including intestinal epithelial cells, lymphocytes and monocytes/macrophages/DC. An important anti-inflammatory effect of TGF-β on the immune system is the promotion and generation of FOXP3-positive regulatory T cells in the intestinal compartment. There are first and encouraging data from the treatment of Crohn's disease, an inflammatory GI condition, that targeted enteral therapy with optimized concentrations of immunoregulatory peptides, such as TGF-β, might of interest for the treatment of inflammatory disorders.

Micronutrients decrease incidence of common infections in type 2 diabetic outpatients

A randomized, double-blind, placebo-controlled trial was carried out to investigate the effects of micronutrients supplementation on immunity and the incidence of common infections in type 2 diabetic outpatients. A total of 196 type 2 diabetic outpatients were randomized to receive tablets of micronutrients (n=97) or placebo (n=99) for 6 months. Individualized dietary energy intake and daily physical activity were recommended. Anthropometric measurements, blood biochemical variables and the incidence of common infections were measured at baseline and at 6 months. Data on diet, exercise and infection (upper respiratory tract infection, skin infection, urinary and genital tract infections, other infections) were recorded 1 month before the study and every month during the study. Blood concentrations of total protein, iron (Fe), folic acid and hemoglobin increased and unsaturated iron-binding capacity(UIBC) levels were decreased in the micronutrients supplementation group compared to the placebo group at 6 months. Moreover, at 6 months, compared to the placebo group, the blood concentrations of IgE, CD4+, CD4+/CD8+, WBC, lymphocyte counts, basophilic leukocyte increased and CD8+ count decreased in the supplementation group, and the levels of IgA, IgM, IgG and complements C3 and C4 did not differ. The incidence of upper respiratory infection, whitlow, dermapostasis, vaginitis, urinary tract infection, gingivitis and dental ulcer were lower and body temperature and duration of fever greatly improved in the supplementation than the placebo group. These data indicated that supplementation of micronutrients might increase immune function and reduce the incidence of common infections in type 2 diabetic outpatients.

Comparative analysis of middle ear immune response and micronutrient level between mucoid and purulent otitis media

OBJECTIVE

To determine the differences in the outcome of treatment, the middle ear immune response, and micronutrient status between patients with purulent (POM) and mucoid (MOM) otitis media.

DESIGN

Children with acute otitis media were recruited, treated, and followed up for between 6 and 10 months. The sera and middle ear secretion (MES) were analyzed for immunoglobulins and zinc using enzyme-linked immunoassay and flame atomic absorption spectrophotometry, respectively. The parameters were compared with selected healthy controls.

SUBJECTS

There were 399 participants: 228 children with acute otitis media selected using the American Academy of Otolaryngology-Head and Neck Surgery criteria and 171 healthy controls, with ages ranging between 6 months and 9 years (mean 7 years; SD 2.32 years).

RESULT

POM accounted for 126 of 228 patients, and MOM accounted for 102. The chronicity of otitis media (using the 3-month duration cutoff) was seen in 87 subjects (46%): 31 of 126 POM subjects and 56 of 102 MOM subjects (p = .002). The serum IgA to IgG ratios were 0.03 and 0.07 among POM and MOM, respectively; however, the MES IgA to IgG ratios were higher, 0.3 and 0.2, for POM and MOM, respectively. This gives a MES to serum ratio of IgA to IgG value of 0.3 to 0.03 (10) for POM and 0.2 to 0.07 (2.67) for MOM, which showed a significant statistical difference (p = .001). The MES to serum ratios of IgE were 0.89 and 1.3 among POM and MOM, respectively (p = .03). There was a significant difference in the serum IgG (p = .019), serum zinc (p = .009), and MES IgA (p = .028) and IgG (p = .01).

CONCLUSION

Chronicity was greater in MOM than in POM; POM had a higher middle ear immune response (measured by the MES to serum ratio of IgA to IgG) and serum zinc than MOM but a lower MES IgE.

HPV-induced recurrent laryngeal papillomatosis: dietary fatty acid and micronutrient intakes

Human papilloma virus (HPV)-induced recurrent laryngeal papillomatosis (RLP) is a chronic debilitating disease often encountered among children of poor socio-economic South African groups. There are a few studies and limited evidence as to what extent nutrition may contribute to this disease. To our knowledge this is the first study that gives an account of dietary FA and micronutrient intakes in RLP patients, according to food frequency questionnaires. The dietary FA profile revealed an excessive linoleic acid (LA) intake syndrome and is also marked by high palmitic acid (PA), oleic acid (OA) and SFA intakes. Research revealed that enhanced LA and PA drive, respectively, mitogenic stimuli and apoptotic resistance during tumorigenesis, whist SFAs are associated with lipid rafts, the Th1 immune response and immunosuppression. Low folate intake, a risk for HPV-infection, and low Zn intake, detrimental for lipid metabolism and immunocompetence, occurred in, respectively, 70% and 20% RLP patients. The poor correlations that were found in RLP patients between essential fatty acids (EFAs) and micronutrients, namely, Mg, Zn and Se, involved in lipid metabolism and immune responses, need proper clarification. Overall, it is plausible that the diet (poor nutrition), a shift in lipid metabolism caused by HPV- infection, environmental smoke and oxidative stress, as well as extra-esophageal acid reflux with secondary inflammation in the larynx are co-factors in the etiology of laryngeal papillomatosis, and that immunocompromised patients are subjected to recurrence. It is imperative to ensure that children with RLP receive proper nutrition and follow a healthy lifestyle to prevent disease recurrence after treatment.

Nutritional factors and immunological ageing

Undernutrition profoundly affects immune responses, particularly at the extremities of life: in infants and in the elderly. The present review focuses on this interrelationship in the elderly. It describes three different stages of ageing: stage 1, healthy ageing, which is observed in very healthy elderly individuals who have no nutritional deficit; stage 2, common ageing, which is observed in most elderly individuals in whom various micronutrient deficits are found; stage 3, pathological ageing, which is observed in patients with protein–energy deficiency. Stage 1, primary immune ageing, is essentially characterized by changes in T-cell subsets but no change in T-cell function; T-cell function is reduced only in the very elderly (>90 years old). Stage 2, secondary immune ageing, is influenced by micronutrient deficits that may be corrected by providing nutritional supplements. Furthermore, immune responses may also be enhanced by supplementation of subjects who have no micronutrient deficits, indicating that the immune system of elderly individuals is highly susceptible to the influence of micronutrients. In stage 3, tertiary immune ageing, the immune responses are strongly related to the decreased nutritional status. In these patients decreased immune responses lead to long-lasting acute-phase responses, which induce greater use of nutritional reserves during disease and lead to increased frailty. As nutritional status has a marked effect on immune responses in elderly individuals, nutritional therapy should be given to elderly individuals who have nutrient deficits, and perhaps also to individuals who do not have nutrient deficits in order to promote healthy ageing and extend the lifespan.

Interactions of malnutrition and immune impairment, with specific reference to immunity against parasites

1. Clinical malnutrition is a heterogenous group of disorders including macronutrient deficiencies leading to body cell mass depletion and micronutrient deficiencies, and these often coexist with infectious and inflammatory processes and environmental problems. 2. There is good evidence that specific micronutrients influence immunity, particularly zinc and vitamin A. Iron may have both beneficial and deleterious effects depending on circumstances. 3. There is surprisingly slender good evidence that immunity to parasites is dependent on macronutrient intake or body composition.

US youths in the early stages of HIV disease have low intakes of some micronutrients important for optimal immune function

OBJECTIVE

We examined the association between micronutrient intakes and human immunodeficiency virus (HIV) infection in youths who were at increased nutritional risk because of the demands of growth and disease as well as poor dietary habits.

DESIGN

This was a cross-sectional study to collect dietary intake data using the Block Food Frequency Questionnaire (98.2). Anthropometric, biochemical, clinical, and sociodemographic data were available.Subjects/Setting Participants included 264 HIV-infected and 127 HIV-uninfected adolescents and young adults from the Reaching for Excellence in Adolescent Care and Health network, a multisite observational study on HIV progression. Statistical analyses CD4(+) T cells were stratified for HIV-infected youths: >/=500, 200 to 499, and <200 cells/microL. Micronutrient intakes were compared by presence of HIV infection, using two-sample Student's t tests. Categoric analyses used chi(2) test. Generalized linear regression determined predictors of vitamins A, C, and E; iron; and zinc intakes.

RESULTS

Almost half (49.0%) of the HIV-infected participants had CD4(+) T cells >/=500 cells/microL. After controlling for other factors, HIV-infected participants with CD4(+) T cells >/=500 had decreased iron intake (P<.05) and tended to be associated with lower intakes of vitamins C and E (P<.10) compared with those with more advanced disease and HIV-uninfected youths. Among those youths with CD4(+) T cells between 200 and 499 cells/microL, a high anxiety score was associated with a sixfold increase in vitamin A intake as compared with those with a low score.Applications/conclusions Given the increased micronutrient requirements, nutrition counseling with HIV-infected youths should focus on early increase of intake of foods rich in micronutrients to improve growth, slow disease progression, and increase survival.

Can a short period of micronutrient supplementation in older institutionalized people improve response to influenza vaccine? A randomized, controlled trial

OBJECTIVES

To test the hypothesis that a micronutrient supplement can improve seroconversion after influenza immunization in older institutionalized people.

DESIGN

: Randomized, double-blind, placebo-controlled study.

SETTING

Nursing and residential homes in Liverpool, United Kingdom.

PARTICIPANTS

One hundred sixty-four residents aged 60 and older from 31 homes were initially randomized; of these, 119 (72.6%) completed the study.

INTERVENTION

Participants were randomized to receive a micronutrient supplement providing the reference nutrient intake for all vitamins and trace elements or identical placebo. Tablets were taken over an 8-week period during September and October 2000; influenza vaccine was administered 4 weeks after their commencement.

MEASUREMENTS

The hemagglutination-inhibiting antibody response as defined by a fourfold or greater titer rise over 4 weeks and assessed separately for each of the three antigens contained in the 2000/2001 influenza vaccine (A/New Caledonia/20/99 (H1N1), A/Moscow/10/99 (H3N2), B/Beijing/184/93 (B)).

RESULTS

Despite a significant increase in serum concentrations of vitamins A, C, D3, E, folate, and selenium in the supplemented group, there was no significant difference between groups (supplemented vs placebo, respectively) in the proportion of participants seroconverting to H1N1 (41% vs 49%, P=.374), H3N2 (49% vs 58%, P=.343), or B (41% vs 40%, P=.944).

CONCLUSION

A micronutrient supplement providing the reference nutrient intake administered over 8 weeks had no beneficial effect on antibody response to influenza vaccine in older people living in long-term care.

Impact of nutritional status on antibody responses to different vaccines in undernourished Gambian children

AIM

To test the efficacy of T-cell-dependent and T-cell-independent vaccines in rural Gambian children suffering from a range of energy/protein and micronutrient deficiencies.

METHODS

Nutritional status (anthropometry, haemoglobin, plasma leptin and micronutrient status) and response to two vaccinations (23 valent pneumococcal capsular polysaccharide vaccine, Pneumovax and the Human Diploid-Cell Rabies Vaccine) were assessed in 472 children aged 6 1/2 h to 9 1/2 y.

RESULTS

Anthropometry and micronutrient status (as z-scores against European reference values) indicated a range from moderate to severe levels of undernutrition [mean (interquartile range): weight-for-age z-score -1.58 (-2.18 to -0.95); height-for-age z-score -0.94 (-1.51 to -0.35); body-mass-index-for-age z-score -1.43 (-2.05 to -0.84); mid-upper arm circumference -1.41 (-1.72 to -1.13); leptin -1.06 (-1.10 to -1.03); haemoglobin (Hb) -0.30 (-1.18 to 0.79); zinc -1.29 (-2.42 to -0.55); vitamin C -0.01 (-1.18 to 1.15); retinol -1.33 (-1.97 to -0.77)]. A seasonal effect was observed in haemoglobin levels and in all micronutrients (with the exception of zinc and retinol) and in the response to vaccination. After adjusting for seasonality, age and gender, no consistent associations were found between any of the measures of nutritional status and the effectiveness of seroconversion to either of the vaccines.

CONCLUSION

The successful short-term seroconversion to whole inactivated viral and bacterial polysaccharide vaccines indicates that the processes leading to antibody secretion remain intact over a wide range of single and combined nutrient deficiencies.

[Importance of vitamin A deficiency in pathology and immunology of viral infections]

Vitamin deficiencies and infections caused by viruses and other pathogens often coexist and exhibit complex interactions. Malnutrition, vitamin A deficiency and infections among populations of the developing countries, these are the leading cause of death, particularly in children. Several micronutrients were in study, vitamin A deficiency is strongly involved in measles and diarrhea. There are also some scientific data against this thesis. These vitamins, virus infection and immune function interactions are briefly reviewed in this article.

Effect of dietary intake on immune function in athletes

Athletes are exposed to acute and chronic stress that may lead to suppression of the immune system and increased oxidative species generation. In addition, the tendency to consume fewer calories than expended and to avoid fats may further compromise the immune system and antioxidant mechanisms. The exercise stress is proportional to the intensity and duration of the exercise, relative to the maximal capacity of the athlete. Muscle glycogen depletion compromises exercise performance and it also increases the stress. Glycogen stores can be protected by increased fat oxidation (glycogen sparing). The diets of athletes should be balanced so that total caloric intake equals expenditure, and so that the carbohydrates and fats utilised in exercise are replenished. Many athletes do not meet these criteria and have compromised glycogen or fat stores, have deficits in essential fats, and do not take in sufficient micronutrients to support exercise performance, immune competence and antioxidant defence. Either overtraining or under nutrition may lead to an increased risk of infections. Exercise stress leads to a proportional increase in stress hormone levels and concomitant changes in several aspects of immunity, including the following: high cortisol; neutrophilia; lymphopenia; decreases in granulocyte oxidative burst, nasal mucociliary clearance, natural killer cell activity, lymphocyte proliferation, the delayed-type sensitivity response, the production of cytokines in response to mitogens, and nasal and salivary immunoglobulin A levels; blunted major histocompatibility complex II expression in macrophages; and increases in blood granulocyte and monocyte phagocytosis, and pro- and anti-inflammatory cytokines. In addition to providing fuel for exercise, glycolysis, glutaminlysis, fat oxidation and protein degradation participate in metabolism and synthesis of the immune components. Compromising, or overusing, any of these components may lead to immunosuppression. In some cases, supplementation with micronutrients may facilitate the immune system and compensate for deficits in essential nutrients. In summary, athletes should eat adequate calories and nutrients to balance expenditure of all nutrients. Dietary insufficiencies should be compensated for by supplementation with nutrients, with care not to over compensate. By following these rules, and regulating training to avoid overtraining, the immune system can be maintained to minimise the risk of upper respiratory tract infections.

Micronutrient malnutrition, infection, and immunity: an overview

Micronutrient deficiencies and infectious diseases often coexist and exhibit complex interactions leading to the vicious cycle of malnutrition and infections among underprivileged populations of the developing countries, particularly in preschool children. Several micronutrients such as vitamin A, beta-carotene, folic acid, vitamin B12 vitamin C, riboflavin, iron, zinc, and selenium, have immunomodulating functions and thus influence the susceptibility of a host to infectious diseases and the course and outcome of such diseases. Certain of these micronutrients also possess antioxidant functions that not only regulate immune homeostasis of the host, but also alter the genome of the microbes, particularly in viruses, resulting in grave consequences like resurgence of old infectious diseases or the emergence of new infections. These micronutrient infection and immune function interactions and their clinical and public health relevance in developing countries are briefly reviewed in this article.

Immunobiology of mild micronutrient deficiencies

Nutrition is a critical determinant of the outcome of host microbe interactions through a modulation of the immune response. Besides macronutrient malnutrition, deficiencies of several macronutrients also influence immune homeostasis and thus affect infection-related morbidity and mortality. Deficiencies of micronutrients like vitamin A, iron and zinc are widely prevalent among populations living in developing countries. Besides their severe deficiencies, subclinical deficiencies are known to impair biological functions in the host, immune function being one of them. The effects of these micronutrients on various immune mechanisms are briefly reviewed in this article.

Micronutrients and host resistance to viral infection

Previous work in our laboratory demonstrated that a virus could undergo rapid mutation in a host deficient in Se, leading to a normally avirulent virus acquiring virulence due to genome changes. Once these mutations occur, even a host with adequate Se-nutriture is susceptible to the newly virulent virus. What influence does the deficiency in Se have on the immune response of the host? Infection with myocarditic strains of coxsackievirus induces an inflammatory response in the cardiac tissue. It is this immune response that induces the heart damage, rather than direct viral effects on the heart tissue. Chemokines are chemo-attractant molecules that are secreted during an infection in order to attract immune cells to the site of the injury, and have been found to be important for the development of coxsackievirus-induced myocarditis. We found that a deficiency in Se influences the expression of mRNA for the chemokine monocyte chemo-attractant protein-1, which may have implications for the development of myocarditis in the Se-deficient host. Expression of mRNA for interferon-gamma was also greatly decreased in the Se-deficient animal. Thus, a deficiency in Se can have profound effects on the host as well as on the virus itself. How the alteration of the immune response of the Se-deficient animal affects the development of the virulent genotype remains to be answered.