Selenium status of a group of Scottish adults

Evaluation of Serum Selenium Status by Age and Gender: A Retrospective Observational Cohort Study in Western Romania

Selenium, residing in a series of selenoproteins, plays an important role in both female and male reproductive function. Of particular significance for reproduction is the antioxidant glutathione peroxidase (GPx), a main selenoenzyme, whose level is regulated by the availability of Se in the body. We hypothesized that changes in Se status, closely related to GPx activity, would result in an increased risk of reproductive dysfunction in individuals. We retrospectively investigated the serum selenium (SeS) concentrations of 1264 apparently healthy people, aged 16–89 years, from Western Romania. The general analysis revealed a non-normal SeS distribution with a median SeS of 100.26 ± 18.32 μg/L and a significant difference in SeS levels between age groups. The analysis of the young group (16–35 years) revealed that up to 50% of individuals did not reach the SeS threshold corresponding to maximum GPx activity (80 μg/L), and a significant imbalance between the genders was apparent when looking at SeS values outside the range. Our results correlated with the general diminished reproductive ability registered in Romania during the last few years. Serum selenium content proves to offer a proper reflection of the fertility competence of the young population, and its monitoring is important for guiding dietary adjustments and attaining normal reproductive function.

Preparation of an experimental mouse model lacking selenium-dependent glutathione peroxidase activities by feeding a selenium-deficient diet

Relatively young (4-week-old) selenium deficient (SeD) mice, which lack the activity of selenium-dependent glutathione peroxidase (GSH-Px) isomers, were prepared using torula yeast-based SeD diet. Mice were fed the torula yeast-based SeD diet and ultra-pure water. Several different timings for starting the SeD diet were assessed. The weekly time course of liver comprehensive GSH-Px activity after weaning was monitored. Protein expression levels of GPx1 and 4 in the liver were measured by Western blot analysis. Gene expression levels of GPx1, 2, 3, 4, and 7 in the liver were measured by quantitative real-time PCR. Apoptotic activity of thymocytes after hydrogen peroxide (H2O2) exposure was compared. Thirty-day survival rates after whole-body X-ray irradiation were estimated. Pre-birth or right-after-birth starting of the SeD diet in dams was unable to lead to creation of SeD mice due to neonatal death. This suggests that Se is necessary for normal birth and healthy growing of mouse pups. Starting the mother on the SeD diet from 2 weeks after giving birth (SeD-trial-2w group) resulted in a usable SeD mouse model. The liver GSH-Px activity of the SeD-trial-2w group was almost none from 4 week olds, but the mice survived for more than 63 weeks. Protein and gene expression of GPx1 was suppressed in the SeD-trial-2w group, but that of GPx4 was not. The thymocytes of the SeD-trial-2w group were sensitive to H2O2-induced apoptosis. The SeD-trial-2w group was sensitive to whole-body X-ray irradiation compared with control mice. The SeD-trial-2w model may be a useful animal model for H2O2/hydroperoxide-induced oxidative stress.

A comprehensive review on environmental transformation of selenium: recent advances and research perspectives

Selenium (Se) is an important micronutrient and essential trace element for both humans and animals, which exist in the environment ubiquitously. Selenium deficiency is an important issue worldwide, with various reported cases of its deficiency. Low selenium contents in some specific terrestrial environments have resulted in its deficiency in humans. However, high levels of selenium in the geochemical environment may have harmful influences and can cause a severe toxicity to living things. Due to its extremely narrow deficiency and toxicity limits, selenium is becoming a serious matter of discussion for the scientists who deals with selenium-related environmental and health issues. Based on available relevant literature, this review provides a comprehensive data about Se sources, levels, production and factors affecting selenium bioavailability/speciation in soil, characteristics of Se, biogeochemical cycling, deficiency and toxicity, and its environmental transformation to know the Se distribution in the environment. Further research should focus on thoroughly understanding the concentration, speciation, Se cycling in the environment and food chain to effectively utilize Se resources, remediate Se deficiency/toxicity, and evaluate the Se states and eco-effects on human health.

Selenium deficiency in subtropical littoral pampas: environmental and dietary aspects

Se deficiency has a critical effect on human health. The littoral near Patos Lagoon in the south of Brazil is composed of Quaternary sandy deposits and nutrient-deficient soils, which contribute to Se deficiency in the surrounding environment. The average concentration of Se in littoral soils is six times lower than the metalloid deficiency threshold of 0.5 mg kg^-1 and is close to that in countries where Keshan disease is registered. The sediments in the Patos Estuary are also notably lower in Se than near-shore marine sediments. Foodstuffs produced in the littoral pampas are characterised by extremely low Se concentrations compared with the same alimentary products reported worldwide. The total daily dietary intake of Se in the region is 24 μg day^-1, which is half the Estimated Average Requirement for adults. Black beans in the local diet provide over 40% of daily Se intake. Prescriptive addition of Se to prevalent products seems the most effective solution to the problem of metalloid dietary deficiency in the region. Similar environmental conditions and significant concentration of the population in the littoral zone suggest that the problem of Se deficiency probably affects a large proportion of the population along the Atlantic coast of Brazil.

Vegetarianism and colorectal cancer risk in a low-selenium environment: effect modification by selenium status? A possible factor contributing to the null results in British vegetarians

BACKGROUND

Despite the consistent findings of lower total cancer incidence in vegetarians than in meat-eaters in the UK, the results of studies of colorectal cancer (CRC) risk in British vegetarians have largely been null. This was in contrast to the hypothesis of a decreased risk of CRC in this population due to null intake of red and processed meats and increased intake of fibre. Although the data are inconsistent, it has been suggested that selenium (Se) status may influence CRC risk.

METHODS

A literature review was performed of studies on CRC risk in vegetarians, Se intakes and status in vegetarians, and changes of Se intakes and status in the UK throughout the follow-up periods of studies on CRC risk in British vegetarians.

RESULTS

Vegetarians in the UK and other low-Se areas were found to have low Se intakes and status compared to non-vegetarians. There was some evidence of a reverse J-shaped curve of Se intakes and status in the UK throughout the last three decades. These presumed patterns were followed by the changes in CRC mortality or incidence in British vegetarians during this period.

CONCLUSIONS

Available data on Se intake and status in British vegetarians, as well as the relationship between their secular changes in the UK and changes in CRC risk in this dietary group, are compatible with the hypothesis that low Se status may contribute to the largely null results of studies of CRC risk in vegetarians in the UK.

Selenium supplementation has beneficial and detrimental effects on immunity to influenza vaccine in older adults

BACKGROUND & AIMS

Mortality resulting from influenza (flu) virus infections occurs primarily in the elderly through declining immunity. Studies in mice have suggested beneficial effects of selenium (Se) supplementation on immunity to flu but similar evidence is lacking in humans. A dietary intervention study was therefore designed to test the effects of Se-supplementation on a variety of parameters of anti-flu immunity in healthy subjects aged 50-64 years.

METHODS

A 12-week randomized, double-blinded, placebo-controlled clinical trial (ClinicalTrials.govNCT00279812) was undertaken in six groups of individuals with plasma Se levels <110 ng/mL. Four groups were given daily capsules of yeast enriched with 0 μg Se/day (SeY-0/d; n = 20), 50 μg Se/d (SeY-50/d; n = 18), 100 μg Se/d (SeY-100/d; n = 21) or 200 μg Se/d (SeY-200/d; n = 23). Two groups were given onion-containing meals with either <1 μg Se/d (SeO-0/d; n = 17) or 50 μg Se/d (SeO-50/d; n = 18). Flu vaccine was administrated at week 10 and immune parameters were assessed until week 12.

RESULTS

Primary study endpoints were changes in cellular and humoral immune responses. Supplementation with SeY and SeO affected different aspects of cellular immunity. SeY increased Tctx-ADCC cell counts in blood (214%, SeY-100/d) before flu vaccination and a dose-dependent increase in T cell proliferation (500%, SeY-50/100/200/d), IL-8 (169%, SeY-100/d) and IL-10 (317%, SeY-200/d) secretion after in vivo flu challenge. Positive effects were contrasted by lower granzyme B content of CD8 cells (55%, SeY-200/d). SeO (Se 50 μg/d) also enhanced T cell proliferation after vaccination (650%), IFN-γ (289%), and IL-8 secretion (139%), granzyme (209%) and perforin (190%) content of CD8 cells but inhibited TNF-α synthesis (42%). Onion on its own reduced the number of NKT cells in blood (38%). These effects were determined by comparison to group-specific baseline yeast or onion control groups. Mucosal flu-specific antibody responses were unaffected by Se-supplementation.

CONCLUSION

Se-supplementation in healthy human adults with marginal Se status resulted in both beneficial and detrimental effects on cellular immunity to flu that was affected by the form of Se, supplemental dose and delivery matrix. These observations call for a thorough evaluation of the risks and benefits associated with Se-supplementation.

Study of selenium intake and disposition in various matrices based on mathematical algorithms derived from pooled biomonitoring data

Biomonitoring is increasingly used to assess exposure to selenium (Se) in the population. However, there is little harmonization among protocols used in the different studies (varying biological matrices, differences in expression of results (concentrations versus amounts, units)). This makes inter-comparison of biomonitoring results across studies difficult. From a public health risk perspective, it also becomes challenging to estimate baseline levels in biological matrices for populations exposed by various sources. The aim of this study was thus to perform a systematic analysis of the relationship between Se intakes and biological concentrations based on published data. Inclusion and exclusion criteria were used and led to select 75 published biomonitoring data in humans from an extended review of Se biomonitoring studies. This represents 8 628 individuals who provided biological samples aiming at documenting Se exposure and/or Se concentrations in two or more biological matrices. Mathematical algorithms that relate Se intakes to biological concentrations and establish matrix-to-matrix associations were derived from these pooled biomonitoring data. Logarithmic regressions showed good correlations between Se intakes and whole blood concentrations (R(2)=0.884), plasma concentrations (R(2)=0.863) and urinary excretion rates (R(2)=0.958). Blood and plasma concentrations were also strongly related (R(2)=0.874), as were whole blood concentrations and urinary excretion rates (R(2)=0.953). The interpretation of the log-regression coefficients allowed illustrating Se physiology. Se concentrations in plasma tend to plateau when daily intake exceed 150 μg/d, whereas Se in urine increases rapidly above this threshold. The application of the algorithms to other independent data sets in order to reconstruct past Se intakes confirmed that interpretation of results on the basis of Se in integuments may be misleading if external contamination is not avoided. This approach based on pooled data covered a wide range of exposure and the large number of data integrated increased the level of confidence of results.

Selenium and preeclampsia: A global perspective

Preeclampsia is a complex multisystem disorder of pregnancy where oxidative stress plays an important aetiological role. The role of selenium in the synthesis of endogenous antioxidants is well documented, and a significant reduction in selenium has been reported in preeclamptic women. The objective of this study was to map global selenium status and preeclampsia incidence. This study identified peer reviewed journal articles reporting national preeclampsia incidence (%) and matched these with reported values of selenium intake and plasma/serum selenium concentrations (μg/L). Matched data were obtained for 45 regions, reporting 6456,570 births, spanning Europe, Asia, Australasia, Africa, North and South America. Increasing plasma selenium concentration was found to be correlated with a reduction in preeclampsia incidence (Pearson's r=-0.604, P<0.0001). Countries with a reported serum/plasma selenium level of ⩾95μg/L were considered selenium sufficient and a significant reduction in preeclampsia incidence for countries above this value (P=0.0007) was noted. Significant reductions in preeclampsia incidence were found to coincide with increases in plasma/serum selenium concentration in the New Zealand (P=0.0003) and Finland (0.0028) populations following Government intervention. This study supports the hypothesis that selenium supplementation may be beneficial in reducing oxidative stress in women at risk of preeclampsia.

Diet and asthma: nutrition implications from prevention to treatment

Asthma is characterized by lung airway inflammation initiated and perpetuated by an inappropriate immune response, increased airway responsiveness, and variable airflow obstruction. In Western countries there has been a marked increase in asthma prevalence such that it has become a public health concern. It has been hypothesized that the increase may be due to changing antioxidant intake, increasing dietary ratio of n-6:n-3 polyunsaturated fatty acids (PUFA), and vitamin D deficiency (and supplementation). Observational studies have reported associations between asthma and dietary antioxidants (vitamin E, vitamin C, carotenoids, selenium, polyphenols, and fruit), PUFA, and vitamin D. However, supplementing the diets of adults with asthma with antioxidants and n-3 PUFA has minimal, if any, clinical benefit. Currently there is insufficient evidence to support the use of nutrient supplements to complement conventional treatment; however, results of ongoing studies are awaited, and additional research is required, particularly in children. Interest in the potential of dietary intervention during pregnancy to reduce the likelihood of childhood asthma has increased. A small number of cohort studies have highlighted associations between childhood asthma and reduced maternal intake of some nutrients (vitamin E, vitamin D, selenium, zinc, and PUFA) during pregnancy. Although vitamin D intervention studies during pregnancy are ongoing and two intervention studies suggest that dietary PUFA manipulation during pregnancy may be advantageous, further trials are needed to establish if modification of maternal nutrient intake during pregnancy can be used as a healthy, low cost, public health measure to reduce the prevalence of childhood asthma.

Aqua regia extractable selenium concentrations of some Scottish topsoils measured by ICP-MS and the relationship with mineral and organic soil components

BACKGROUND

To provide information concerning the geographical distribution of selenium (Se) in the soils of Scotland, we analysed 47 arable soils selected on the basis of their parent rock, which were expected to have relatively high, low or unclassified Se concentrations. To investigate relationships between the actual minerals in the soils and the aqua regia extractable Se concentration of the soil, soil minerals were quantified by X-ray diffraction.

RESULTS

The aqua regia extractable Se concentrations of the soils were between 0.19 and 1.46 mg kg(-1). No simple correlation between the aqua regia extractable Se concentrations of the soil and the parent rock classification estimated by soil survey was evident. Partial least squares analysis revealed that the aqua regia extractable Se concentration of the soils was positively related to loss on ignition (LOI) or C concentration and negatively related to the K-feldspar concentration, with other minerals being less important.

CONCLUSION

The Se concentration of arable topsoils from Scotland is more related to LOI or carbon concentration, with parent material being less important.

Establishing optimal selenium status: results of a randomized, double-blind, placebo-controlled trial

BACKGROUND

Dietary recommendations for selenium differ between countries, mainly because of uncertainties over the definition of optimal selenium status.

OBJECTIVE

The objective was to examine the dose-response relations for different forms of selenium.

DESIGN

A randomized, double-blind, placebo-controlled dietary intervention was carried out in 119 healthy men and women aged 50-64 y living in the United Kingdom. Daily placebo or selenium-enriched yeast tablets containing 50, 100, or 200 microg Se ( approximately 60% selenomethionine), selenium-enriched onion meals ( approximately 66% gamma-glutamyl-methylselenocysteine, providing the equivalent of 50 microg Se/d), or unenriched onion meals were consumed for 12 wk. Changes in platelet glutathione peroxidase activity and in plasma selenium and selenoprotein P concentrations were measured.

RESULTS

The mean baseline plasma selenium concentration for all subjects was 95.7 +/- 11.5 ng/mL, which increased significantly by 10 wk to steady state concentrations of 118.3 +/- 13.1, 152.0 +/- 24.3, and 177.4 +/- 26.3 ng/mL in those who consumed 50, 100, or 200 microg Se-yeast/d, respectively. Platelet glutathione peroxidase activity did not change significantly in response to either dose or form of selenium. Selenoprotein P increased significantly in all selenium intervention groups from an overall baseline mean of 4.99 +/- 0.80 microg/mL to 6.17 +/- 0.85, 6.73 +/- 1.01, 6.59 +/- 0.64, and 5.72 +/- 0.75 microg/mL in those who consumed 50, 100, or 200 microg Se-yeast/d and 50 microg Se-enriched onions/d, respectively.

CONCLUSIONS

Plasma selenoprotein P is a useful biomarker of status in populations with relatively low selenium intakes because it responds to different dietary forms of selenium. To optimize the plasma selenoprotein P concentration in this study, 50 microg Se/d was required in addition to the habitual intake of approximately 55 microg/d. In the context of established relations between plasma selenium and risk of cancer and mortality, and recognizing the important functions of selenoprotein P, these results provide important evidence for deriving estimated average requirements for selenium in adults. This trial was registered at clinicaltrials.gov as NCT00279812.

Session 1: Allergic disease: Nutrition as a potential determinant of asthma

Asthma is characterised by chronic lung airway inflammation, increased airway responsiveness and variable airflow obstruction. In Westernised countries asthma is a public health concern because of its prevalence, associated ill health and high societal and healthcare costs. In recent decades there has been a marked increase in asthma prevalence, particularly in Westernised countries. It has been proposed that changing diet has contributed to the increase in asthma. Several dietary hypotheses exist; the first relates the increase in asthma to declining dietary antioxidant intake, the second to decreased intake of long-chain n-3 PUFA and increasing intake of n-6 PUFA. Vitamin D supplementation and deficiency have also been hypothesised to have contributed to the increase in asthma. Observational studies have reported associations between asthma and dietary antioxidants (vitamin E, vitamin C, carotenoids, Se, flavonoids, fruit), lipids (PUFA, butter, margarine, fish) and vitamin D. However, supplementing the diets of adults with asthma with antioxidants and lipids has minimal, if any, clinical benefit. There is growing interest in the possibility that childhood asthma is influenced by maternal diet during pregnancy, with studies highlighting associations between childhood asthma and maternal intake of some nutrients (vitamin E, vitamin D, Se, PUFA) during pregnancy. It has been suggested that maternal diet during pregnancy influences fetal airway and/or immune development. Further intervention studies are needed to establish whether modification of maternal nutrient intake during pregnancy can be used as a healthy low-cost public health measure to reduce the prevalence of childhood asthma.

Antioxidants and allergic disease: a case of too little or too much?

Speculation persists as to the possible role, if any, of dietary antioxidants in allergic disease. While it has been hypothesized that the recent increase in allergic disease is a consequence of declining dietary antioxidant intake, an alternative hypothesis proposes that the increase in allergic disease is due to increasing antioxidant intake. Dietary trends are conflicting; the intake of some antioxidants has declined, for others intakes are likely to have increased. Animal model studies demonstrate that antioxidant supplementation at the time of primary and subsequent allergen exposure attenuates allergic inflammatory responses. The data from human studies are less clear. Observational epidemiological studies of humans are beset by several methodological limitations associated with the assessment of diet and predominantly focus on asthma. Most observational studies report potentially beneficial associations between dietary antioxidants and allergic outcomes, but a small minority report potentially adverse associations. Human intervention studies suggest that single antioxidant supplements confer minimal, if any clinical benefit in adults with asthma, however, there is still scope for studies in children, atopic dermatitis, allergic rhinitis (AR) and of antioxidant combinations. More recently, it has been suggested that dietary antioxidants in the developmental context of fetal and infant development influence the development childhood asthma and atopic sensitization possibly by affecting the first interactions between the neonatal immune system and allergens. While a small number of birth cohort studies have reported potentially beneficial associations between maternal intake of some antioxidants during pregnancy and childhood asthma, there is very limited data suggesting associations between maternal antioxidant intake and childhood atopic dermatitis and AR. The available epidemiological, animal, molecular and immunological data suggest that there are associations between antioxidants and asthma and to a much lesser extent, atopic dermatitis and AR. However, the exact nature of the relationships and the potential for therapeutic intervention remain unclear.

Selenium in Critically Ill Patients

There is increasing evidence that particular nutritional substrates may be important in critically ill patients and in recent years there has been growing interest in selenium. This review aims to outline the incidence of selenium deficiency in critically ill patients, the consequences of such a deficiency and present the evidence for, and effect of, selenium supplementation in these patients. Selenium levels fall during periods of oxidative stress as occurs in critically ill patients with conditions such as severe sepsis, burns, and following trauma. Data from individual studies and meta-analyses suggests that selenium is an important adjuvant therapy in certain critically ill patients and supplementation of selenium may offer a mortality benefit.

Longitudinal selenium status in healthy British adults: assessment using biochemical and molecular biomarkers

Human selenium (Se) requirements are currently based on biochemical markers of Se status. In rats, tissue glutathione peroxidase-1 (Gpx1) mRNA levels can be used effectively to determine Se requirements; blood Gpx1 mRNA levels decrease in Se-deficient rats, so molecular biology-based markers have potential for human nutrition assessment. To study the efficacy of molecular biology markers for assessing Se status in humans, we conducted a longitudinal study on 39 subjects (age 45 +/- 11) in Reading, UK. Diet diaries (5 day) and blood were obtained from each subject at 2, 8, 17 and 23 weeks, and plasma Se, glutathione peroxidase (Gpx3) enzyme activity, and selenoprotein mRNA levels were determined. There were no significant longitudinal effects on Se biomarkers. Se intake averaged 48 +/- 14 microg/d. Plasma Se concentrations averaged 1.13 +/- 0.16 micromol/l. Plasma Se v. energy-corrected Se intake (ng Se/kJ/d) was significantly correlated, but neither Gpx3 activity v. Se intake (ng Se/kJ/d) nor Gpx3 activity v. plasma Se was significantly correlated. Collectively, this indicates that subjects were on the plateaus of the response curves. Selenoprotein mRNAs were quantitated in total RNA isolated from whole blood, but mRNA levels for Gpx1, selenoprotein H, and selenoprotein W (all highly regulated by Se in rodents), as well selenoprotein P, Gpx3, and phospholipid hydroperoxide glutathione peroxidase were also not significantly correlated with plasma Se. Thus selenoprotein molecular biomarkers, as well as traditional biochemical markers, are unable to further distinguish differences in Se status in these Se replete subjects. The efficacy of molecular biomarkers to detect Se deficiency needs to be tested in Se-deficient populations.

Early childhood wheezing symptoms in relation to plasma selenium in pregnant mothers and neonates

OBJECTIVE

Reduced dietary selenium intake has been linked to the development of asthma. We have investigated whether childhood wheezing symptoms, and asthma up to the age of 5 years are associated with plasma selenium and erythrocyte glutathione peroxidase (GPx) concentrations in pregnant mothers and neonates.

METHODS

Two thousand pregnant women were recruited and their 1924 singleton children followed up. Plasma selenium and erythrocyte GPx concentrations were measured in maternal blood during early pregnancy (12 weeks gestation) and in neonatal cord blood. Cohort children were followed up at 1, 2 and 5 years using a respiratory symptom questionnaire and at 5 years children were also invited for spirometry and skin-prick test (SPT). Maternal and neonatal plasma selenium and erythrocyte GPx were related to the childhood outcomes of wheezing, and asthma.

RESULTS

At 2 years 1282 children were followed up. At 5 years symptom data were available for 1167 children, 700 children were SPT tested, and forced expiratory volume in 1 s (FEV(1)) was measured in 478. Maternal plasma selenium concentration during early pregnancy was inversely associated with wheezing (odds ratio per 10 microg/kg plasma selenium 0.86, 95% confidence interval 0.76-0.97), and consulting a doctor because of wheeze (0.79, 0.69-0.93) in the second year of life. Cord plasma selenium was also inversely associated with wheezing (0.67, 0.47-0.96), and consulting a doctor because of wheeze (0.62, 0.41-0.93) in the second year of life. By age 5 these associations had disappeared. Maternal and neonatal erythrocyte GPx concentrations were not associated with any childhood outcomes at 2 or 5 years.

CONCLUSION

The selenium status of mothers during early pregnancy, and neonates is associated with early childhood wheezing but not asthma or atopic sensitization, furthermore, this association is absent by the age of 5 years.

Early life events in asthma--diet

It has been hypothesized that the recent increase in the prevalence of asthma may, in part, be a consequence of changing diet. There is now increasing interest in the possibility that childhood asthma may be influenced by maternal diet during pregnancy and/or diet during early childhood. A number of observational studies and a childhood fish oil supplementation study provide little support for the notion that early childhood intake of polyunsaturated fatty acids (PUFAs) influence the development of childhood asthma. Recent work however, suggests that supplementation of maternal diet with fish oil is associated with altered neonatal immune responses to allergens. Further work is required to establish whether this immunological observation is translated into clinical outcomes. Two birth cohorts have now reported reduced maternal intake of vitamin E, zinc and vitamin D during pregnancy to be associated with increased asthma and wheezing outcomes in children up to the age of 5 years. Early life diet could modulate the likelihood of childhood asthma by affecting fetal airway development and/or influencing the initial early life interactions between allergens and the immune system. In animal models, vitamin E, zinc and vitamin D have been shown to modify fetal lung development and vitamin E, zinc, vitamin D and PUFA can modulate T-cell responses. Further research, particularly, early life intervention studies need to be carried out to establish whether early life dietary intervention can be used as a public health measure to reduce the prevalence of childhood asthma.

Selenium in global food systems

Food systems need to produce enough of the essential trace element Se to provide regular adult intakes of at least 40 μg/d to support the maximal expression of the Se enzymes, and perhaps as much as 300 μg/d to reduce risks of cancer. Deprivation of Se is associated with impairments in antioxidant protection, redox regulation and energy production as consequences of suboptimal expression of one or more of the Se-containing enzymes. These impairments may not cause deficiency signs in the classical sense, but instead contribute to health problems caused by physiological and environmental oxidative stresses and infections. At the same time, supranutritional intakes of Se, i.e. intakes greater than those required for selenocysteine enzyme expression, appear to reduce cancer risk. The lower, nutritional, level is greater than the typical intakes of many people in several parts of the world, and few populations have intakes approaching the latter, supranutritional, level. Accordingly, low Se status is likely to contribute to morbidity and mortality due to infectious as well as chronic diseases, and increasing Se intakes in all parts of the world can be expected to reduce cancer rates.

Selenium supplementation: does soil supplementation help and why?

There are now concerns that dietary Se intake is inadequate for the population in the UK and parts of Europe. Many different methods can be proposed to deal with this problem. Experience from Finland suggests that the addition of Se to fertiliser is a safe and effective means of increasing the intake of the micronutrient in the human population. However, careful consideration needs to be given to the potential consequences of increasing Se intake. It is important to understand the biochemical and physiological changes that may occur with any increase in Se intake within the UK population. Se is an essential component of at least twenty functional proteins within mammals. These proteins are essential for a range of metabolic functions, including antioxidant activity, thyroid hormone synthesis and immune function. Thus, any increase in Se intake has the potential to influence in a wide range of factors that may impinge on the incidence of chronic disease. Treatment of soil with Se-supplemented fertiliser will certainly increase total Se in food products derived from areas where this treatment is in place. Consumption of such foods will increase Se status in many populations where the existing intake does not meet requirements. If the increases in Se intake are not toxic the overall consequences have the potential to be beneficial.

Selenium and glutathione peroxidases in blood of patients with different stages of chronic renal failure

In patients with chronic renal failure (CRF) Se concentration in blood components is usually lower as compared with healthy controls. One of the five known forms of Se-dependent glutathione peroxidases (GSH-Px), the plasma GSH-Px, is synthesized primarily in the kidney. In CRF patients, plasma GSH-Px activity is reduced and the reduction increases with the progress of the disease. The Se concentration in blood components was measured spectrofluorometrically with 2,3-diaminonaphthalene as complexing reagent. Activities of GSH-Px in red cells and in plasma were assayed by the coupled method with t-butyl hydroperoxide as substrate. The study group consisted of 150 patients in different stages of CRF. The results were compared with the values for 30 healthy subjects. Se concentrations in whole blood and plasma of the entire group of patients were significantly lower (p < 0.01) as compared with the healthy subjects. In the incipient stage, however, the Se levels in all blood components were non-significantly lower. In whole blood and plasma the Se levels gradually decreased, reaching in the end stage values that were lower by 29 to 32% (p < 0.0001) as compared with the control group. Total protein and albumin levels in plasma of patients were significantly lower (p < 0.0001) as compared with healthy subjects and they decreased linearly with the progress of the disease. Positive and highly significant correlations were noted between total plasma protein and plasma Se concentrations (p < 0.0001) as well as between plasma albumin and plasma Se concentrations (p < 0.0001). Red cell GSH-Px activity in the entire group of patients was lower (p < 0.05) than in the control group and did not change significantly with the progress of the disease. In plasma, however, GSH-Px activity of the entire group was lower by 33% (p < 0.0001) as compared with healthy subjects and decreased gradually with increasing renal failure. Highly significant, inverse correlations were seen between creatinine levels and plasma GSH-Px activities (p < 0.0001) as well as between urea nitrogen levels and plasma GSH-Px activities (p < 0.0001) when all stages of the disease were included. In conclusion, patients with CRF exhibit lower Se levels in blood components as compared with healthy subjects. In whole blood and plasma these levels decrease with the progress of the disease. Plasma GSH-Px activity in patients was extremely reduced and it dramatically decreased with the progress of the illness.

Comparison of the serum selenium content of healthy adults living in the Antwerp region (Belgium) with recent literature data

Graphite furnace atomic absorption spectrometry, after improved matrix modification and using Zeeman background correction, was used to measure the serum selenium content of healthy adults living in the Antwerp region (Belgium). The mean serum concentration of 13 men and 13 women, sampled once a month during 1 year, was 84.3 +/- 9.4ng/ml with a broad range of 51.4-121.7 ng/ml. The intra-individual variation was remarkably high. Recent literature on selenium concentrations is reviewed and values are tabulated, with limitation to healthy adults and European countries. The mean serum selenium concentration measured corresponded well to older literature data for Belgium. The obtained values were found to be in the medium range compared with the literature data for other European countries.

Markers of the validity of reported energy intake

Energy intake (EI) is the foundation of the diet, because all other nutrients must be provided within the quantity of food needed to fulfill the energy requirement. Thus if total EI is underestimated, it is probable that the intakes of other nutrients are also underestimated. Under conditions of weight stability, EI equals energy expenditure (EE). Because at the group level weight may be regarded as stable in the timescale of a dietary assessment, the validity of reported EI can be evaluated by comparing it with either measured EE or an estimate of the energy requirement of the population. This paper provides the first comprehensive review of studies in which EI was reported and EE was measured using the doubly labeled water technique. These conclusively demonstrate widespread bias to the underestimation of EI. Because energy requirements of populations or individuals can be conveniently expressed as multiples of the basal metabolic rate (BMR), EE:BMR, reported EI may also be expressed as EI:BMR for comparison. Values of EI:BMR falling below the 95% confidence limit of agreement between these two measures signify the presence of underreporting. A formula for calculating the lower 95% confidence limit was proposed by Goldberg et al. (the Goldberg cutoff). It has been used by numerous authors to identify individual underreporters in different dietary databases to explore the variables associated with underreporting. These studies are also comprehensively reviewed. They explore the characteristics of underreporters and the biases in estimating nutrient intake and in describing meal patterns associated with underreporting. This review also examines some of the problems for the interpretation of data introduced by underreporting and particularly by variable underreporting across subjects. Future directions for research are identified.

Essentiality and toxicity of selenium and its status in Australia: a review

Selenium (Se) is an essential trace element for animals and humans because of its role in an antioxidant enzyme glutathione peroxidase. This enzyme protects cell membranes from damage caused by the peroxidation of lipids. The paper provides an overview of the effects of Se toxicity and deficiency in humans and animals. It is well established that Se deficiency causes health implications in humans and animals. Se is also very toxic and can cause Se poisoning (selenosis) in humans and animals. In Australia, Se deficiency has caused health problem to livestock; however, the problems were eliminated after the introduction of Se supplementation. Se toxicity has also been reported in some regions of Australia as a result of livestock feeding on Se accumulative plant species. The major source of Se is diet, and in many regions of the world the levels of Se in the soils generally reflect the Se status in human populations. In foods, the bioavailability and toxicity of Se depend on its chemical forms. Generally, organic forms of Se are more bioavailable and less toxic than the inorganic forms (selenites, selenates). The Se status in the Australian population and how this is compared with the rest of the world is also discussed.

Intracellular trafficking of micronutrients: from gene regulation to nutrient requirements

The intracellular distribution of micronutrients, as well as their uptake, is important for cell function. In some cases the distribution of micronutrients or their related proteins is determined by gene expression mechanisms. The 3' untranslated region (3'UTR) of metallothionein-1 mRNA determines localisation of the mRNA, and in turn intracellular trafficking of the protein product. Using transfected cells we have evidence for the trafficking of metallothionein-1 into the nucleus and for its involvement in protection from oxidative stress and DNA damage. When nutritional supply of Se is limited, selenoprotein expression is altered, but not all selenoproteins are affected equally; the available Se is prioritised for synthesis of particular selenoproteins. The prioritisation involves differences in mRNA translation and stability due to 3'UTR sequences. Potentially, genetic variation in these regulatory mechanisms may affect nutrient requirements. Genetic polymorphisms in the 3'UTR from two selenoprotein genes have been observed; one polymorphism affects selenoprotein synthesis. These examples illustrate how molecular approaches can contribute at several levels to an increased understanding of nutrient metabolism and requirements. First, they provide the tools to investigate regulatory features in genes and their products. Second, understanding these processes can provide model systems to investigate nutrient metabolism at the cellular level. Third, once key features have been identified, the availability of human genome sequence information and single nucleotide polymorphism databases present possibilities to define the extent of genetic variation in genes of nutritional relevance. Ultimately, the functionality of any variations can be defined and subgroups of the population with subtly different nutrient requirements identified.

A novel single nucleotide polymorphism in the 3' untranslated region of human glutathione peroxidase 4 influences lipoxygenase metabolism

Selenium (Se) is an essential micronutrient for human health. The biological roles of the essential micronutrient Se are attributed to its presence in a range of 20-30 selenoproteins including the cytosolic and phospholipid hydroperoxide glutathione peroxidases (GPX1 and GPX4). It has been suggested that GPX4 may play a role in regulation of leukotriene biosynthesis and thus inflammation. In eukaryotes Se is incorporated into selenoproteins as the amino acid selenocysteine in a process requiring a stem-loop within the 3' untranslated region (3'UTR) of the mRNA. In this study the region of the GPX4 gene corresponding to the 3'UTR was scanned for mutations in a group of 66 volunteers. The data show a T/C variant at position 718. The distribution of this SNP in our population was 34% CC, 25% TT and 41% TC; i.e., it is in Hardy-Weinberg equilibrium. Individuals of different genotypes exhibited significant differences in the levels of lymphocyte 5-lipoxygenase total products, with C718 showing increased levels of those products compared to T718 and T/C718 (36% and 44% increases, respectively). The data suggest that the SNP718 that we have identified has functional effects and support the hypothesis that GPX4 plays a regulatory role in leukotriene biosynthesis.

Predictive value of human biomonitoring in environmental medicine: experiences at the outpatient unit of environmental medicine (UEM) of the University Hospital Aachen, Germany

There is little data on the distribution of biomonitoring parameters in patients at outpatient Units of Environmental Medicine (UEM). We evaluated the biomonitoring parameters of 646 UEM outpatients from our University Hospital 1988-1998. Few patients were exposed to specific substances. Data of patients who were not obviously exposed was analysed statistically (geometric mean, standard deviation, median, 95th percentile). Results were compared with reference values in literature. Normal distribution of biomonitoring parameters was rare. 95th percentiles for arsenic, chromium, selenium, zinc, phenol and toluene were below standard, 95th percentiles for copper and mercury above, and 95th percentiles for lead, cadmium, pentachlorophenol, lindane, and beta-hexachlorocyclohexane were within the published range of reference values. Thallium as well as most volatile organic compounds analyzed were below detection levels. Aluminum and fluorine exposure was rarely analysed. In view of these results, it is concluded that the indication for biomonitoring needs to be stringent as levels of biomonitoring parameters are generally not risen in patients of the UEM.

The argument for increasing selenium intake

The essential trace mineral, Se, is of fundamental importance to human health. As a constituent of selenoproteins it plays both structural and enzymic roles, in the latter context being best known as an antioxidant and catalyst for the production of active thyroid hormone. While Se-deficiency diseases have been recognised for some time, evidence is mounting that less-overt deficiency can also cause adverse health effects and furthermore, that supra-nutritional levels of Se may give additional protection from disease. In the context of these effects, low or diminishing Se status in some parts of the world, notably in some European countries such as the UK, is giving cause for concern. While deficiency has an adverse effect on immunocompetence, Se supplementation appears to enhance the immune response. Se appears to be a key nutrient in counteracting certain viral infections; thus, in a Se-deficient host the benign coxsackie virus becomes virulent, causing heart damage, the influenza virus causes more serious lung pathology and HIV infection progresses more rapidly to AIDS. Long recognised as essential for successful animal reproduction, Se is required for human sperm maturation and sperm motility and may reduce the risk of miscarriage. Deficiency has been linked to adverse mood states. Findings have been equivocal in linking Se to cardiovascular disease risk, although other conditions involving oxidative stress and inflammation have shown some association with Se status. There is growing evidence that higher Se intakes are associated with reduced cancer risk. While persuasive evidence already exists to suggest that additional Se would be beneficial in some health conditions, results from intervention trials underway or planned have the potential to reinforce or refute the argument for increasing Se intake.

Selenium status of Irish adults: evidence of insufficiency

BACKGROUND

Sub-optimal selenium status may have a role in the aetiology of various pathologies. Selenium status depends on adequate selenium in the diet. A relatively high proportion of Irish adults (17% men; 46% women) have an inadequate dietary intake.

AIM

A study was designed to examine the selenium status of healthy Irish adults.

METHODS

Ninety-one healthy Irish adults, aged 18-67 years, were recruited from the Cork City area. A fasting blood sample was collected from each subject and each was assayed for serum selenium an index of serum selenium.

RESULTS

Mean (+/- SD) serum selenium concentration in healthy Irish adults was 76 (+/- 21)microg/l. There was no significant difference in values between males and females or between postmenopausal and premenopausal women or between the three main age categories.

CONCLUSION

Current serum selenium values of Irish adults would not appear to be sufficient to achieve optimal activity of glutathione peroxidase, which occurs at serum selenium concentration around 95microg/l. Sub-optimal selenium status may increase susceptibility to various chronic disorders.

Selenium status and its correlates in a British national diet and nutrition survey: people aged 65 years and over

Plasma selenium (Se) concentrations were measured in 1134 British people aged 65 years and over, living in mainland Britain during 1994-1995. Eight hundred and eighty-three lived in the community ("free-living"), while the remainder lived in institutions (residential and nursing homes). The overall mean plasma Se concentrations was 0.90 micromol/l (inner 95% range 0.50-1.36 micromol/l). Free-living people had significantly higher values than counterparts living in institutions, and there was an overall inverse correlation with age. Plasma Se varied with season (lower from October to December than at other times of the year), while values were higher in southern Britain than in the North. Socio-economic associations also existed (lower plasma Se in people receiving state benefits or with poorer educational attainment), while smokers had lower values than non-smokers. Several indices of poor health status or of medicine use were correlated with lower plasma Se, which was also predicted by several biochemical or haematological indices of infection or inflammation. Plasma Se was strongly and directly correlated with plasma albumin, zinc, cholesterol, vitamin C, several carotenoids, alpha-tocopherol, pyridoxal phosphate, and with blood haemoglobin and several anthropometric indices. All relationships were independent of age and gender, and are consistent with the view that plasma Se levels are higher in fit and well-nourished elderly people and lower in those who are frail, poorly-nourished and unwell. Whole-blood glutathione peroxidase generally did not share these relationships, was only very weakly correlated with plasma Se, and appeared to be less useful as a status indicator in this population group.

Selenium, selenoproteins and human health: a review

Selenium is of fundamental importance to human health. It is an essential component of several major metabolic pathways, including thyroid hormone metabolism, antioxidant defence systems, and immune function. The decline in blood selenium concentration in the UK and other European Union countries has therefore several potential public health implications, particularly in relation to the chronic disease prevalence of the Western world such as cancer and cardiovascular disease. Ten years have elapsed since recommended dietary intakes of selenium were introduced on the basis of blood glutathione peroxidase activity. Since then 30 new selenoproteins have been identified, of which 15 have been purified to allow characterisation of their biological function. The long term health implications in relation to declining selenium intakes have not yet been thoroughly examined, yet the implicit importance of selenium to human health is recognised universally. Selenium is incorporated as selenocysteine at the active site of a wide range of selenoproteins. The four glutathione peroxidase enzymes (classical GPx1, gastrointestinal GPx2, plasma GPx3, phospholipid hydroperoxide GPx4)) which represent a major class of functionally important selenoproteins, were the first to be characterised. Thioredoxin reductase (TR) is a recently identified seleno-cysteine containing enzyme which catalyzes the NADPH dependent reduction of thioredoxin and therefore plays a regulatory role in its metabolic activity. Approximately 60% of Se in plasma is incorporated in selenoprotein P which contains 10 Se atoms per molecule as selenocysteine, and may serve as a transport protein for Se. However, selenoprotein-P is also expressed in many tissues which suggests that although it may facilitate whole body Se distribution, this may not be its sole function. A second major class of selenoproteins are the iodothyronine deiodinase enzymes which catalyse the 5'5-mono-deiodination of the prohormone thyroxine (T4) to the active thyroid hormone 3,3'5-triiodothyronine (T3). Sperm capsule selenoprotein is localised in the mid-peice portion of spermatozoa where it stabilises the integrity of the sperm flagella. Se intake effects tissue concentrations of selenoprotein W which is reported to be necessary for muscle metabolism. It is of great concern that the health implications of the decline in Se status in the UK over the past two decades have not been systematically investigated. It is well recognised that dietary selenium is important for a healthy immune response. There is also evidence that Se has a protective effect against some forms of cancer; that it may enhance male fertility; decrease cardiovascular disease mortality, and regulate the inflammatory mediators in asthma. The potential influence of Se on these chronic diseases within the European population are important considerations when assessing Se requirement.

The importance of selenium to human health

The essential trace mineral, selenium, is of fundamental importance to human health. As a constituent of selenoproteins, selenium has structural and enzymic roles, in the latter context being best-known as an antioxidant and catalyst for the production of active thyroid hormone. Selenium is needed for the proper functioning of the immune system, and appears to be a key nutrient in counteracting the development of virulence and inhibiting HIV progression to AIDS. It is required for sperm motility and may reduce the risk of miscarriage. Deficiency has been linked to adverse mood states. Findings have been equivocal in linking selenium to cardiovascular disease risk although other conditions involving oxidative stress and inflammation have shown benefits of a higher selenium status. An elevated selenium intake may be associated with reduced cancer risk. Large clinical trials are now planned to confirm or refute this hypothesis. In the context of these health effects, low or diminishing selenium status in some parts of the world, notably in some European countries, is giving cause for concern.

A comparison of methods of assessment of dietary selenium intakes in Otago, New Zealand

The aims of the present study were (1) to compare three methods of assessment of dietary Se intake, i.e. chemical analysis of duplicate diets, diet records and a food-frequency questionnaire (FFQ) designed specifically for Se, and (2) to determine dietary Se intakes of residents of Otago, New Zealand. The FFQ was completed by 110 free-living adults. Diet records (3 d) and duplicate diet collections were carried out by forty-three of these subjects chosen on the basis of low blood Se concentration, and during a period when consumption of the high-Se foods fish, kidney, liver and Brazil nuts was discouraged. Mean Se intakes were similar for duplicate diet analysis (29 (SD 13) micrograms/d) and diet record assessments (28 (SD 15) micrograms/d). Estimates of intakes from the FFQ for the subgroup of forty-three subjects were higher (51 (SD 26) micrograms/d) than those from duplicate diets and diet records. Values from duplicate diet analysis and diet record assessments were strongly correlated (r 0.7, P = 0.0001), but difference plots indicated a lack of agreement between the two methods. Thus, diet record assessment was not adequate for predicting dietary Se intakes of individuals. Significant correlations were found for relationships between Se intake from duplicate diets (microgram/kg body weight per d) and plasma Se, Se intake from diet records (microgram/d and microgram/kg body weight per d) and plasma Se; and Se intake from the FFQ and whole-blood Se. Se intakes from duplicate diets and diet records were similar to those reported previously for New Zealanders, but lower than the recommended intakes in the USA (National Research Council, 1989), Australia (Truswell et al. 1990) and the UK (Department of Health, 1991) and the World Health Organization/Food and Agriculture Organization/International Atomic Energy Agency (1996) normative requirement.