Bioavailability of selenium from fish, yeast and selenate: a comparative study in humans using stable isotopes

Maternal Seafood Consumption during Pregnancy and Cardiovascular Health of Children at 11 Years of Age

Nutrition is critical during pregnancy for the healthy growth of the developing infant, who is fully dependent on maternal dietary omega-3 supply for development. Fatty fish, a main dietary source of omega-3, is associated with decreased cardiovascular risk in adults. We conducted a longitudinal study based on a mother-offspring cohort as part of the project Infancia y Medio Ambiente (INMA) in order to assess whether fish intake during pregnancy relates to cardiovascular health in children. A total of 657 women were included and followed throughout pregnancy until birth, and their children were enrolled at birth and followed up until age 11-12. A semi-quantitative food frequency questionnaire was used to assess the daily intake of foods during the 1st and 3rd trimesters of pregnancy. Cardiovascular assessments included arterial stiffness (assessed by carotid-femoral pulse wave velocity [PWV]) and retinal microcirculation (photographic assessment of central retinal arteriolar and venular equivalent [CRAE and CRVE]). The association between maternal fish consumption and cardiovascular outcomes of offspring at 11 years of age was evaluated using multivariable linear regression models. There were no statistically significant differences in any cardiovascular endpoint in children whose mothers had a higher fish consumption during pregnancy compared to those with a lower fish consumption. We found a slightly higher PWV (β = 0.1, 95% CI = 0.0; 0.2, p for trend = 0.047) in children whose mothers had a higher consumption of canned tuna during the 1st trimester of pregnancy. Fish intake during pregnancy was found to be unrelated to the offspring's cardiovascular health at 11 years of age. The beneficial cardiovascular effects of fish consumption during pregnancy on the offspring are still inconclusive.

Selenium - a scoping review for Nordic Nutrition Recommendations 2023

Selenium is an essential trace element in humans, critical to the normal physiology in all animal species. The main form of selenium in food is selenomethionine, selenocysteine and a variety of organic compounds, while inorganic salts mainly occur in food supplements. In animals and humans, selenium occurs as selenocysteine in selenoproteins encoded by 25 genes (specific selenium pool). Several selenoproteins are part of the antioxidant enzyme system and serve as oxido-reductases and in thyroid hormone regulation. SelenoproteinP (SELENOP) transports selenium to peripheral tissues, is the main plasma selenoprotein, and has been used as biomarker of selenium status and intake. SELENOP in plasma represents a saturable pool of selenium and is maximised at a selenium concentration in plasma of about 110 µg/L or an intake of selenomethionine at about 1.2 µg/kg body weight in adults. In Finland, with an estimated selenium intake of 88 µg/day in men and 68 µg/day in women, the average selenium concentration in plasma is about 110 µg/L. Imported wheat from selenium rich areas is an important dietary source in Norway. Dietary intakes in the Nordic and Baltic area vary from 39 to 88 µg/day in men and 22 to 68 µg/day in women, the highest levels were from Finland. Most intervention trials on the effect of selenium supplementation on health outcomes have been carried out in 'selenium-replete'-populations and show no beneficial effect, which from a nutritional point of view would rather not be expected. Some intervention studies conducted in populations low in selenium have showed a beneficial effect. Observational studies suggest an inverse relationship between selenium status and risk of cardiovascular diseases (CVDs), cancer and all-cause mortality, and some other outcomes at low levels of intake (<55 µg/day) or in plasma or serum (<100 µg/L). However, a lack of quantitative data and inconsistencies between studies precludes these studies to be used to derive dietary reference values. At high intakes above 330 to 450 µg/day selenium may cause toxic effects affecting liver, peripheral nerves, skin, nails, and hair. An upper tolerable level (UL) of 255 µg selenium/day in adults was established by EFSA.

Quantitative risk-benefit assessment of Portuguese fish and other seafood species consumption scenarios

Portugal has high fish/seafood consumption, which may have both risks and benefits. This study aims to quantify the net health impact of hypothetical scenarios of fish/seafood consumption in the Portuguese population using a risk-benefit assessment methodology. Consumption data from the National Food, Nutrition and Physical Activity Survey 2015-2016 (n 5811) were used to estimate the mean exposure to methylmercury and EPA + DHA in the current and the alternative scenarios considered. Alternative scenarios (alt) were modelled using probabilistic approaches to reflect substitutions from the current consumption in the type of fish/seafood (alt1: excluding predatory fishes; alt2: including only methylmercury low-level fishes) or in the frequency of weekly fish/seafood consumption (alt3 to alt6: 1, 3, 5 or 7 times a week, replacing fish/seafood meals with meat or others). The overall health impact of these scenarios was quantified using disability-adjusted life years (DALY). In the Portuguese population, about 11 450 DALY could be prevented each year if the fish/seafood consumption increased to a daily basis. However, such a scenario would result in 1398 extra DALY considering the consumption by pregnant women and the respective risk on fetal neurodevelopment. Our findings support a recommendation to increase fish/seafood consumption up to 7 times/week. However, for pregnant women and children, special considerations must be proposed to avoid potential risks on fetal neurodevelopment due to methylmercury exposure.

Evaluation of dietary selenium methionine levels and their effects on growth performance, antioxidant status, and meat quality of intensively reared juvenile Hypophthalmichthys molitrix

The objective of this study was to optimize the organic selenium (Se) requirements of intensively reared silver carp (Hypophthalmichthys molitrix). A total of n = 300 juveniles silver carp 11.40±0.52 cm long, and average weighing 25.28±0.18 grams were randomly assigned to 15 aquaria (20 fish/100L aquaria) and subjected to five different dietary Se levels in a completely randomized design. The diets were pelleted supplemented with exogenous Se methionine @ 0.0, 0.3, 0.6, 0.9 and 1.2 mg/kg of the diet. The fourteen days of aquaria acclimatization was given to fish and then an 84-day feeding trial was conducted. The group supplemented with 0.9 mg/kg Se had greater feed intake, gain in length, body weight %, and specific growth rate with a better feed conversion ratio as compared to those fed on the rest of the dietary levels or control (P<0.05). The deposition of Se was greater in the liver, and kidneys of the fishes fed on diets containing 0.9 and 1.2 mg Se levels than in the rest of the treatments (P<0.05). However, dietary Se levels had no effects on the bioaccumulation of Se in muscle tissues (P>0.05). The proximate analysis showed that dry matter, crude protein, and fat contents of meat were not changed (P>0.05) by dietary treatments. Similarly, values of TBARS, RBCs, Hb, and blood glucose contents were similar (P>0.05) across the treatments. However, the concentration of WBCs, HCT, and MCHC was greater in those groups fed on 0.9 and 1.2 Se levels than in those fed on 0.6, 0.3, and 0.0 Se levels respectively (P<0.05). The activities of ALT, AST, and ALP were lowered in the 0.9 mg Se supplemented fishes compared with the rest of the treatments (P<0.05). The SOD, catalases, and GPx levels for muscle, liver, and whole body were greater (P<0.05) in the Se-supplemented groups than in the control. These outcomes indicated that up to 0.9 mg/kg inclusion of methionine-based Se in the diet of juvenile silver carp improved the growth performance, feed conversion ratio, organs Se enrichment, and antioxidant status without any compromise on meat quality.

Deciphering the immunoboosting potential of macro and micronutrients in COVID support therapy

The immune system protects human health from the effects of pathogenic organisms; however, its activity is affected when individuals become infected. These activities require a series of molecules, substrates, and energy sources that are derived from diets. The consumed nutrients from diets help to enhance the immunity of infected individuals as it relates to COVID-19 patients. This study aims to review and highlight requirement and role of macro- and micronutrients of COVID-19 patients in enhancing their immune systems. Series of studies were found to have demonstrated the enhancing potentials of macronutrients (carbohydrates, proteins, and fats) and micronutrients (vitamins, copper, zinc, iron, calcium, magnesium, and selenium) in supporting the immune system's fight against respiratory infections. Each of these nutrients performs a vital role as an antiviral defense in COVID-19 patients. Appropriate consumption or intake of dietary sources that yield these nutrients will help provide the daily requirement to support the immune system in its fight against pathogenic viruses such as COVID-19.

Human mercury exposure levels and fish consumption at the French Riviera

Humans are exposed to methylmercury (MeHg), a bioaccumulative neurotoxin, mainly through the consumption of marine fish. Several studies showed that high MeHg exposure can lead to neurological damage. This is particularly relevant for pregnant women, because MeHg exposure negatively impacts foetal development. Populations living near the sea are generally at increased exposure risk due to higher consumption of fish and seafood. Here, we present the first study of MeHg exposure levels of the population living at the French Riviera, using mercury (Hg) concentrations in hair as a proxy for MeHg exposure. We found that older people that consume more fish presented the highest hair Hg concentrations. Compared to other Mediterranean bordering countries and other European countries, the southern France population is among those with high MeHg exposure (median for women of childbearing age is 0.56 μg g^-1). A global implementation of the Minamata Convention is necessary to lower MeHg exposure of the population.

In vitro assessment of bioavailability of selenium from a processed Japanese anchovy, Niboshi

Niboshi is a commonly used foodstuff that is processed from Japanese anchovy (Engraulis japonicus) in Japanese cuisine. It was previously demonstrated that Niboshi and its water extract contained highly bioavailable selenium for selenium deficient mice. In this study, we assessed the selenium bioavailability from the extract of the Niboshi, using cultured cells. The activity of selenium-dependent glutathione peroxidase (GPx) of rat dorsal ganglion cells and human cervical carcinoma cells incubated with selenium from the Niboshi extract was over 2 times of that of the extract-free control cells and comparable to that of cells incubated with selenious acid of the same selenium concentration. These results suggest that selenium from the Niboshi extract was utilized for synthesis of the selenoprotein. Such in vitro selenium bioavailability was consistent with our previous results of in vivo assessment in mice.

Genetic polymorphism in selenoprotein P modifies the response to selenium-rich foods on blood levels of selenium and selenoprotein P in a randomized dietary intervention study in Danes

Background

Selenium is an essential trace element and is suggested to play a role in the etiology of a number of chronic diseases. Genetic variation in genes encoding selenoproteins, such as selenoprotein P and the glutathione peroxidases, may affect selenium status and, thus, individual susceptibility to some chronic diseases. In the present study, we aimed to (1) investigate the effect of mussel and fish intake on glutathione peroxidase enzyme activity and (2) examine whether single nucleotide polymorphisms in the GPX1, GPX4, and SELENOP genes modify the effect of mussel and fish intake for 26 weeks on whole blood selenium, plasma selenoprotein P concentrations, and erythrocyte GPX enzyme activity in a randomized intervention trial in Denmark.

Results

CC homozygotes of the SELENOP/rs3877899 polymorphism who consumed 1000 g fish and mussels per week for 26 consecutive weeks had higher levels of both selenoprotein P (difference between means - 4.68 ng/mL (95% CI - 8.49, - 0.871)) and whole blood selenium (difference between means - 5.76 (95% CI - 12.5, 1.01)) compared to fish and mussel consuming T-allele carriers although the effect in whole blood selenium concentration was not statistically significant.

Conclusions

Our study indicates that genetically determined variation in SELENOP leads to different responses in expression of selenoproteins following consumption of selenium-rich foods. This study also emphasizes the importance of taking individual aspects such as genotypes into consideration when assessing risk in public health recommendations.

Socio-demographic, lifestyle, and dietary determinants of essential and possibly-essential trace element levels in adipose tissue from an adult cohort

There is increasing evidence linking levels of trace elements (TEs) in adipose tissue with certain chronic conditions (e.g., diabetes or obesity). The objectives of this study were to assess concentrations of a selection of nine essential and possibly-essential TEs in adipose tissue samples from an adult cohort and to explore their socio-demographic, dietary, and lifestyle determinants. Adipose tissue samples were intraoperatively collected from 226 volunteers recruited in two public hospitals from Granada province. Trace elements (Co, Cr, Cu, Fe, Mn, Mo, Se, V, and Zn) were analyzed in adipose tissue by high-resolution inductively coupled plasma mass spectrometry (HR-ICP-MS). Data were collected on socio-demographic characteristics, lifestyle, diet, and health status by face-to-face interview. Predictors of TE concentrations were assessed by using multivariable linear and logistic regression. All TEs were detected in all samples with the exception of Se (53.50%). Iron, zinc, and copper showed the highest concentrations (42.60 mg/kg, 9.80 mg/kg, and 0.68 mg/kg, respectively). Diet was the main predictor of Cr, Fe, Mo, and Se concentrations. Body mass index was negatively associated with all TEs (β coefficients = -0.018 to -0.593, p = 0.001-0.090) except for Mn and V. Age showed a borderline-significant positive correlation with Cu (β = 0.004, p = 0.089). Residence in a rural or semi-rural area was associated with increased Co, Cr, Fe, Mo, Mn, V and Zn concentrations and with β coefficients ranging from 0.196 to 0.544 (p < 0.05). Furthermore, individuals with higher educational level showed increased Cr, Co, Fe and V concentrations (β coefficients = 0.276-0.368, p = 0.022-0.071). This is the first report on the distribution of these TEs in adipose tissue and on their determinants in a human cohort and might serve as an initial step in the elucidation of their clinical relevance.

Diet composition and serum levels of selenium species: A cross-sectional study

Selenium is a trace element of both nutritional and toxicological interest, depending on its dose and chemical form. Diet is the primary source of exposure for most individuals. We sought to investigate the influence of food intake on serum levels of selenium species. Among fifty subjects randomly selected from a Northern Italian population, we assessed dietary habits using a validated semi-quantitative food frequency questionnaire. We also measured circulating levels of selenium species in serum using high pressure liquid chromatography associated with inductively-coupled plasma dynamic reaction cell mass spectrometer. Circulating levels of inorganic selenium, the most toxic selenium species, were positively associated with intake of fish, legumes and dry fruits, and inversely associated with intake of dairy products and mushrooms. Concerning the organic selenium species, selenoproteinP-bound selenium was inversely associated with intake of fish, fresh fruits, vegetables, and legumes, while selenocysteine-bound selenium positively associated with intake of fresh fruit, potato, legume and mushroom. In the present study, intakes of different foods were correlated with different types of selenium species. These results have important public health implications when assessing the nutritional and toxicological potential of diet composition with reference to selenium exposure.

Portuguese preschool children: Benefit (EPA+DHA and Se) and risk (MeHg) assessment through the consumption of selected fish species

This study aimed to assess the risk-benefit balance associated to fish consumption by Portuguese preschool children. For this purpose, databases (from IPMA and literature) were mined and mathematically processed by a model based on the Extreme Value Theory assuming consumption scenarios. Eicosapentaenoic (EPA) and docosahexaenoic acid (DHA) and selenium (Se) and methylmercury (MeHg) were selected as critical components of fish, given their health impact and significant contents in some fish species. Assessment also took into account that Se may protect against MeHg toxicity. With exception of blue shark, Se Health Benefit Value (Se-HBV), was always positive (ranging between 3.3 and 14.9) and Se:MeHg ratio was always higher than one (3.8 to 32.3). It was also estimated that the deleterious effects of MeHg on children IQ were offset by the beneficial impact of EPA+DHA in fish except for grilled black scabbardfish consumed every day. Blue shark, regardless of the culinary treatment, yielded very high probabilities of exceeding MeHg TWI (higher than 84 % with a single weekly meal), thus raising serious concerns. EPA+DHA benefits were high in salmon regardless of culinary treatment (> 84 %). Fish consumption by children is advisable with exception of blue shark and boiled and grilled tuna.

Stable isotope compounds - production, detection, and application

Stable isotopes are used in wide fields of application from natural tracers in biology, geology and archeology through studies of metabolic fluxes to their application as tracers in quantitative proteomics and structural biology. We review the use of stable isotopes of biogenic elements (H, C, N, O, S, Mg, Se) with the emphasis on hydrogen and its heavy isotope deuterium. We will discuss the limitations of enriching various compounds in stable isotopes when produced in living organisms. Finally, we overview methods for measuring stable isotopes, focusing on methods for detection in single cells in situ and their exploitation in modern biotechnologies.

Biomonitoring of 29 trace elements in whole blood from inhabitants of Cotonou (Benin) by ICP-MS

This study aimed to investigate the blood concentration of 29 trace elements, metals or metalloids, in a healthy population of Cotonou not directly exposed to metals in order to propose reference values. Blood samples from 70 blood donors were collected in K2 EDTA tubes for trace elements during September 2015 and a questionnaire was used to assess lifestyle exposure. Blood metal concentrations were determined by inductively coupled plasma mass spectrometry (ICP-MS) equipped with a quadrupole-based reaction cell. Among the selected blood donors 51.4% were aged from 18 to 36 years and 49.6% from 37 to 65 years. Among the 29 elements analyzed As, Pb, Mn, Pd, Sb, Co, Se, Sr showed blood concentrations higher than the reference values found in the literature for non-exposed healthy European populations and their geometric means were respectively 5.81; 47.39; 19.71; 1.91; 7.50; 0.66; 163.01; 30.53μg/L. This study provides the first reference value (5th-95th percentiles) for each element in Cotonou, which enables us to carry out further investigations on environmental and occupational exposure.

Effects of preparation on nutrient and environmental contaminant levels in Arctic beluga whale (Delphinapterus leucas) traditional foods

For Canadian Arctic indigenous populations, marine mammal (MM) traditional foods (TFs) represent sources of both important nutrients and hazardous environmental contaminants. Food preparation is known to impact the nutrient and environmental contaminant content of processed items, yet the impacts of preparation on indigenous Arctic MM TFs remain poorly characterized. In order to determine how the various processes involved in preparing beluga blubber TFs affect their levels of nutrients and environmental contaminants, we collected blubber samples from 2 male beluga whales, aged 24 and 37 years, captured during the 2014 summer hunting season in Tuktoyaktuk, Northwest Territories, and processed them according to local TF preparation methods. We measured the levels of select nutrients [selenium (Se), polyunsaturated fatty acids (PUFAs)] and contaminants [organochlorine pesticides, perfluoroalkyl and polyfluoroalkyl substances (PFASs), polybrominated diphenyl ethers, polychlorinated biphenyls, polycyclic aromatic hydrocarbons (PAHs), mercury (Hg)] in raw and prepared (boiled, roasted, aged) beluga blubber TFs. The impacts of beluga blubber TF preparation methods on nutrient and environmental contaminant levels were inconsistent, as the majority of processes either did not appear to influence concentrations or affected the two belugas differently. However, roasting and ageing beluga blubber consistently impacted certain compounds: roasting blubber increased concentrations of hydrophilic substances (Se and certain PFASs) through solvent depletion and deposited PAHs from cookfire smoke. The solid-liquid phase separation involved in ageing blubber depleted hydrophilic elements (Se, Hg) and some ionogenic PFASs from the lipid-rich liquid oil phase, while PUFA levels appeared to increase, and hydrophobic persistent organic pollutants were retained. Ageing blubber adjacent to in-use smokehouses also resulted in considerable PAH deposition to processed samples. Our findings demonstrated that contaminant concentration differences were greater between the two sets of whale samples, based on age differences, than they were within each set of whale samples, due to variable preparation methods. When considering means to minimize human contaminant exposure while maximizing nutrient intake, consumption of aged liquid from younger male whales would be preferred, based on possible PUFA enhancement and selective depletion of hydrophilic environmental contaminants in this food item.

Bioaccessibility of selenium from cooked rice as determined in a simulator of the human intestinal tract (SHIME)

BACKGROUND

As an essential but also potentially toxic element, both overexposure and underexposure to selenium (Se) can significantly affect public health. Rice is a common source of Se, especially in Asia. Not all Se may be released from the rice and become available for absorption into the bloodstream upon digestion in the gastrointestinal tract. Therefore, the bioaccessibility of Se in cooked white (polished) rice was assessed in vitro using the static gastrointestinal simulator SHIME (Simulator of the Human Intestinal Microbial Ecosystem).

RESULTS

The common cooking procedure in China prior to consumption [i.e. boiling at low rice:water ratios (1:3) until all of the water is absorbed into the rice] did not change total Se levels in the rice. Gastrointestinal digestion of the cooked rice matrix revealed a Se bioaccessibility of 67-76% of total Se. Subsequent microbial activity in the colon reduced the accessibility of Se in the cooked rice to 51-62%.

CONCLUSION

Not all Se present in cooked white rice should be considered as being bioavailable in the small intestine. A minor part is transferred with the remaining food matrix to the colon, where it is available for the microbial metabolism. © 2017 Society of Chemical Industry.

Modulation of selenium tissue distribution and selenoprotein expression in Atlantic salmon (Salmo salar L.) fed diets with graded levels of plant ingredients

Increased substitution of marine ingredients by terrestrial plant products in aquafeeds has been proven to be suitable for Atlantic salmon farming. However, a reduction in n-3 long-chain PUFA is a consequence of this substitution. In contrast, relatively little attention has been paid to the effects of fishmeal and oil substitution on levels of micronutrients such as Se, considering fish are major sources of this mineral for human consumers. To evaluate the effects of dietary marine ingredient substitution on tissue Se distribution and the expression of Se metabolism and antioxidant enzyme genes, Atlantic salmons were fed three feeds based on commercial formulations with increasing levels of plant proteins (PP) and vegetable oil. Lipid content in flesh did not vary at any sampling point, but it was higher in the liver of 1 kg of fish fed higher PP. Fatty acid content reflected dietary input and was related to oxidation levels (thiobarbituric acid-reactive substances). Liver had the highest Se levels, followed by head kidney, whereas the lowest contents were found in brain and gill. The Se concentration of flesh decreased considerably with high levels of substitution, reducing the added value of fish consumption. Only the brain showed significant differences in glutathione peroxidase, transfer RNA selenocysteine 1-associated protein 1b and superoxide dismutase expression, whereas no significant regulation of Se-related genes was found in liver. Although Se levels in the diets satisfied the essential requirements of salmon, high PP levels led to a reduction in the supply of this essential micronutrient.

Benefits and risks associated with consumption of raw, cooked, and canned tuna (Thunnus spp.) based on the bioaccessibility of selenium and methylmercury

The Se, Hg, and methylmercury (MeHg) levels in raw, cooked (boiled and grilled), and canned tuna (Thunnus spp.) were determined before and after an in vitro digestion, thereby enabling the calculation of the respective bioaccessibility percentages. A risk-benefit evaluation of raw and canned tuna on the basis of the Se and MeHg data was performed. Selenium bioaccessibility was high in tuna, though slightly lower in canned than in raw products. Mercury levels were high in raw and cooked tuna. Hg bioaccessibility percentages were low (39-48%) in the cooked tuna and even lower (<20%) in canned tuna. For the bioaccessible fraction, all molar Se:MeHg ratios were higher than one (between 10 and 74). A probabilistic assessment of MeHg risk vs Se benefit showed that while a weekly meal of canned tuna presents very low risk, raw, boiled, and grilled tuna consumption should not exceed a monthly meal, at least, for pregnant and nursing women.

The effect on selenium concentrations of a randomized intervention with fish and mussels in a population with relatively low habitual dietary selenium intake

Selenium status of the Danish population is below that assumed optimal for the suggested protective effects against chronic diseases, including certain cancers. Fish and shellfish are important dietary sources of selenium in Denmark. We investigated the effect of increased fish and mussel intake on selenium blood concentrations in a population with relatively low habitual dietary selenium intake. We randomly assigned 102 healthy men and women (all non-smokers) aged 48–76 years to an intervention group (n = 51) or a control group (n = 51). Intervention participants received 1000 g fish and mussels/week for 26 weeks (~50 μg selenium/day). Controls received no intervention. Non-fasting blood samples were taken and whole blood selenium was determined using inductively coupled plasma-mass spectrometry (ICP-MS), and plasma selenoprotein P (SelP) was determined by high performance liquid chromatography coupled to ICP-MS. All available observations were included in linear multiple regression analysis to evaluate the effect of the intervention. The difference in mean change for intervention compared with control persons was 14.9 ng/mL (95% CI: 10.2, 19.7) for whole blood selenium, and 7.0 ng/mL (95% CI: 3.1, 10.9) for plasma SelP (Weeks 0–26). Selenium concentrations were significantly increased after 26 weeks of intervention, albeit to a lower degree than expected.

Identification and determination of selenoneine, 2-selenyl-N α , N α , N α -trimethyl-L-histidine, as the major organic selenium in blood cells in a fish-eating population on remote Japanese Islands

Selenoneine is the major selenium compound in fish muscles, and fish appears to be an important source of selenium in the fish-eating population. Selenoneine has strong antioxidant activity and a detoxifying function against methylmercury (MeHg) toxicity. Dietary intake, bioaccumulation, and metabolism of selenoneine have not been characterized in humans. A nutritional survey was conducted in remote islands of the Kagoshima Prefecture in Japan. To evaluate the potential risks and benefits of fish consumption for health, we measured concentrations of selenoneine, total selenium, MeHg, inorganic mercury, and polyunsaturated fatty acid (LC-PUFA) in the blood of a fish-eating human population. The erythrocyte, leukocyte, and platelet residues following removal of serum (cellular fraction) contained 0.510 μg Se/g, 0.212 μg selenoneine Se/g, and 0.262 μg Se-containing proteins Se/g, whereas the serum contained 0.174 μg total Se/g. Selenoneine was highly concentrated in the cellular fraction in a manner that was dependent on subjects' frequency of fish consumption. Concentrations of selenoneine were closely correlated with concentrations of MeHg in the cellular fraction. Selenoneine is the major chemical form of selenium in the blood cells of this fish-eating human population and may be an important biomarker for selenium redox status.

Dietary organic selenium improves growth, survival and resistance to Vibrio mimicus in cultured marron, Cherax cainii (Austin, 2002)

To determine the effects of dietary organic selenium (OS) supplementation on the growth performance and immune competence of marron, Cherax cainii (Austin, 2002), a group of marron were fed 0.2 g kg(-1) of Sel-Plex(®) supplemented basal diet and then compared with another group (control) of marron fed basal diet without any supplementation. After 90 days of feeding, final weight, average weekly gains (AWG), relative gain rate (RGR), specific growth rate (SGR), survival, total and differential haemocyte counts (THC and DHC), were compared between the two groups. Surviving marron from each group were then divided into three sub-groups (three tanks per sub-group with seven marron per tank); (1) first sub-group was injected with 20 μL of 3.24 × 10(6) cfu Vibrio mimicus; (2) the second sub-group was injected with 20 μL normal saline and (3) the third sub-group was not subjected to injection and became the control group. THC, DHC, neutral red retention time (NRRT) and Vibrio ranks of post-injected marron were evaluated for 96 h, at every 24-h interval. The results showed that after 90 days of feeding, final weight, AWG, RGR, SGR, survival, THC, proportion of hyaline cells of OS-fed marron were significantly higher (P < 0.05) than the control group, whereas proportion of granular and semigranular cells were not affected by dietary OS. After challenging with V. mimicus, survival rate of marron without dietary OS significantly decreased (P < 0.05) as compared to the control group of marron. THC of marron in all sub-groups were significantly reduced (P < 0.05) after the challenge. However, THC and granular cells of sub-groups fed OS were higher than other sub-groups. Vibrio ranks and NRRT of marron fed OS were significantly lower and slower, respectively, than marron fed without OS. These findings demonstrated the benefits of OS inclusion in the marron diet in terms of growth, health and disease resistance.

Health benefits of seafood; is it just the fatty acids?

There is a considerable body of literature suggesting a wide range of health benefits associated with diets high in seafood. However, the demand for seafood across the world now exceeds that available from capture fisheries. This has created a rapidly increasing market for aquaculture products, the nutrient composition of which is dependent on feed composition. The use of fishmeal in this food chain does little to counteract the environmental impact of fisheries and so the on-going development of alternative sources is to be welcomed. Nevertheless, an in-depth understanding as to which nutrients in seafood provide benefit is required to permit the production of foods of maximal health benefit to humans. This paper reviews our current knowledge of the beneficial nutrient composition of seafood, in particular omega-3 fatty acids, selenium, taurine, vitamins D and B12, in the context of the development of environmentally sustainable aquaculture.

Blood selenium levels and contribution of food groups to selenium intake in adolescent girls in Iceland

BACKGROUND/OBJECTIVES

Significant changes have been reported in dietary habits and food availability in Iceland that would be expected to compromise selenium intake and status, especially among young people. These include substantial decreases in the consumption of fish and milk, as well as the selenium content of imported wheat. The aim of this study was to assess selenium in the diet and whole blood of adolescent girls, as well as define the most important foods contributing to intake and blood concentrations of selenium.

DESIGN

The subjects were 96 randomly selected girls, aged 16-20, who answered a validated food frequency questionnaire (FFQ) for dietary assessment. Selenium intake from each food group was calculated in µg/day. Blood samples were collected for measurement of whole blood selenium.

RESULTS

Mean dietary selenium was 51±25 µg/day. Milk/dairy products, including cheese, contributed 36±14% of total dietary selenium; fish 18±12%; and bread/cereal products 13±6%. Mean whole blood selenium was 117±12 µg/l (range 90-208); nearly 90% of subjects were above the optimal level of 100 µg/l. Fish and bread/cereal products were the only foods significantly correlated with selenium in blood (r=0.32; P=0.002 and r=0.22; P=0.04, respectively) while no correlation was found with milk and dairy products in spite of their greater contribution to total selenium intake.

CONCLUSION

In this population of Icelandic adolescent girls, selenium intake and status seem acceptable. Judging from associations between intake and blood levels, fish and cereals may be the most important contributors to blood selenium.

(n-3) fatty acids and cardiovascular health: are effects of EPA and DHA shared or complementary?

Considerable research supports cardiovascular benefits of consuming omega-3 PUFA, also known as (n-3) PUFA, from fish or fish oil. Whether individual long-chain (n-3) PUFA have shared or complementary effects is not well established. We reviewed evidence for dietary and endogenous sources and cardiovascular effects on biologic pathways, physiologic risk factors, and clinical endpoints of EPA [20:5(n-3)], docosapentaenoic acid [DPA, 22:5(n-3)], and DHA [22:6(n-3)]. DHA requires direct dietary consumption, with little synthesis from or retroconversion to DPA or EPA. Whereas EPA is also largely derived from direct consumption, EPA can also be synthesized in small amounts from plant (n-3) precursors, especially stearidonic acid. In contrast, DPA appears principally derived from endogenous elongation from EPA, and DPA can also undergo retroconversion back to EPA. In experimental and animal models, both EPA and DHA modulate several relevant biologic pathways, with evidence for some differential benefits. In humans, both fatty acids lower TG levels and, based on more limited studies, favorably affect cardiac diastolic filling, arterial compliance, and some metrics of inflammation and oxidative stress. All three (n-3) PUFA reduce ex vivo platelet aggregation and DHA also modestly increases LDL and HDL particle size; the clinical relevance of such findings is uncertain. Combined EPA+DHA or DPA+DHA levels are associated with lower risk of fatal cardiac events and DHA with lower risk of atrial fibrillation, suggesting direct or indirect benefits of DHA for cardiac arrhythmias (although not excluding similar benefits of EPA or DPA). Conversely, EPA and DPA, but not DHA, are associated with lower risk of nonfatal cardiovascular endpoints in some studies, and purified EPA reduced risk of nonfatal coronary syndromes in one large clinical trial. Overall, for many cardiovascular pathways and outcomes, identified studies of individual (n-3) PUFA were relatively limited, especially for DPA. Nonetheless, the present evidence suggests that EPA and DHA have both shared and complementary benefits. Based on current evidence, increasing consumption of either would be advantageous compared to little or no consumption. Focusing on their combined consumption remains most prudent given the potential for complementary effects and the existing more robust literature on cardiovascular benefits of their combined consumption as fish or fish oil for cardiovascular benefits.

Human urinary excretion and metabolism of (82)Se-enriched selenite and selenate determined by LC-ICP-MS

Urinary excretion of selenium after ingestion of isotope labeled selenite and selenate was studied in seven healthy volunteers, 4 men and 3 women (age 28-50 years). An aqueous solution containing 330 μL (82)Se-selenate (corresponding to 74.3 μg (82)Se) was given orally and urine samples were subsequently collected during the following 24 hours. The scheme was repeated four weeks later with a 280 μL (82)Se-selenite solution (corresponding to 74.4 μg (82)Se). The amount of total Se in the urine samples was determined by inductively coupled mass spectrometry. The mean total urinary excretion of (82)Se following (82)Se-selenate administration was 33.7% (range 15.6-42.5%) while the mean total excretion of (82)Se after (82)Se-selenite administration was 3.2% (range 2.8-3.9%) of the ingested amount. LC-ICPMS analysis of the urine samples showed that the majority of the selenium excreted after selenate ingestion was unchanged selenate for 6 of the individuals while one individual had metabolized a fraction (approx. 20%) of the selenate to selenosugar. Ingestion of 10 times larger doses of selenite in two individuals resulted in 13-23% excretion primarily excreted as selenosugar. These results show that the human metabolic pathways of selenite and selenate are different and indicate that not all selenate, although well absorbed, may be available for the beneficial health effects.

Omega-3 fatty acids and cardiovascular disease: effects on risk factors, molecular pathways, and clinical events

We reviewed available evidence for cardiovascular effects of n-3 polyunsaturated fatty acid (PUFA) consumption, focusing on long chain (seafood) n-3 PUFA, including their principal dietary sources, effects on physiological risk factors, potential molecular pathways and bioactive metabolites, effects on specific clinical endpoints, and existing dietary guidelines. Major dietary sources include fatty fish and other seafood. n-3 PUFA consumption lowers plasma triglycerides, resting heart rate, and blood pressure and might also improve myocardial filling and efficiency, lower inflammation, and improve vascular function. Experimental studies demonstrate direct anti-arrhythmic effects, which have been challenging to document in humans. n-3 PUFA affect a myriad of molecular pathways, including alteration of physical and chemical properties of cellular membranes, direct interaction with and modulation of membrane channels and proteins, regulation of gene expression via nuclear receptors and transcription factors, changes in eicosanoid profiles, and conversion of n-3 PUFA to bioactive metabolites. In prospective observational studies and adequately powered randomized clinical trials, benefits of n-3 PUFA seem most consistent for coronary heart disease mortality and sudden cardiac death. Potential effects on other cardiovascular outcomes are less-well-established, including conflicting evidence from observational studies and/or randomized trials for effects on nonfatal myocardial infarction, ischemic stroke, atrial fibrillation, recurrent ventricular arrhythmias, and heart failure. Research gaps include the relative importance of different physiological and molecular mechanisms, precise dose-responses of physiological and clinical effects, whether fish oil provides all the benefits of fish consumption, and clinical effects of plant-derived n-3 PUFA. Overall, current data provide strong concordant evidence that n-3 PUFA are bioactive compounds that reduce risk of cardiac death. National and international guidelines have converged on consistent recommendations for the general population to consume at least 250 mg/day of long-chain n-3 PUFA or at least 2 servings/week of oily fish.

Cerebral gene expression in response to single or combined gestational exposure to methylmercury and selenium through the maternal diet

Controversy remains regarding the safety of consuming certain types of seafood, particularly during pregnancy. While seafood is rich in vital nutrients, it may also be an important source of environmental contaminants such as methylmercury (MeHg). Selenium (Se) is one essential element present in seafood, hypothesised to ameliorate MeHg toxicity. The aim of the present study was to ascertain the impact of Se on MeHg-induced cerebral gene expression in a mammalian model. Microarray analysis was performed on brain tissue from 15-day-old mice that had been exposed to MeHg throughout development via the maternal diet. The results from the microarray analysis were validated using qPCR. The exposure groups included: MeHg alone (2.6 mg kg(-1)), Se alone (1.3 mg kg(-1)), and MeHg + Se. MeHg was presented in a cysteinate form, and Se as Se-methionine, one of the elemental species occurring naturally in seafood. Eight genes responded to Se exposure alone, five were specific to MeHg, and 63 were regulated under the concurrent exposure of MeHg and Se. Significantly enriched functional classes relating to the immune system and cell adhesion were identified, highlighting potential ameliorating mechanisms of Se on MeHg toxicity. Key developmental genes, such as Wnt3 and Sparcl1, were also identified as putative ameliorative targets. This study, utilising environmentally realistic forms of toxicants, delivered through the natural route of exposure, in association with the power of transcriptomics, highlights significant novel information regarding putative pathways of selenium and MeHg interaction in the mammalian brain.

Recent advances in understanding the role of diet and obesity in the development of colorectal cancer

Colorectal cancer (CRC) is a major cause of premature death in the UK and many developed countries. However, the risk of developing CRC is well recognised to be associated not only with diet but also with obesity and lack of exercise. While epidemiological evidence shows an association with factors such as high red meat intake and low intake of vegetables, fibre and fish, the mechanisms underlying these effects are only now being elucidated. CRC develops over many years and is typically characterised by an accumulation of mutations, which may arise as a consequence of inherited polymorphisms in key genes, but more commonly as a result of spontaneously arising mutations affecting genes controlling cell proliferation, differentiation, apoptosis and DNA repair. Epigenetic changes are observed throughout the progress from normal morphology through formation of adenoma, and the subsequent development of carcinoma. The reasons why this accumulation of loss of homoeostatic controls arises are unclear but chronic inflammation has been proposed to play a central role. Obesity is associated with increased plasma levels of chemokines and adipokines characteristic of chronic systemic inflammation, and dietary factors such as fish oils and phytochemicals have been shown to have anti-inflammatory properties as well as modulating established risk factors such as apoptosis and cell proliferation. There is also some evidence that diet can modify epigenetic changes. This paper briefly reviews the current state of knowledge in relation to CRC development and considers evidence for potential mechanisms by which diet may modify risk.

Discovery of the strong antioxidant selenoneine in tuna and selenium redox metabolism

A novel selenium-containing compound, selenoneine, has been isolated as the major form of organic selenium in the blood and tissues of tuna. Selenoneine harbors a selenium atom in the imidazole ring, 2-selenyl-N(α), N(α), N(α)-trimethyl-L-histidine, and is a selenium analog of ergothioneine. This selenium compound has strong antioxidant capacity and binds to heme proteins, such as hemoglobin and myoglobin, to protect them from iron auto-oxidation, and it reacts with radicals and methylmercury (MeHg). The organic cations/carnitine transporter OCTN1 transports selenoneine and MeHg, regulates Se-enhanced antioxidant activity, and decreases MeHg toxicity. Thus, the dietary intake of selenoneine, by consuming fish, might decrease the formation of reactive oxygen radicals that could oxidize nucleotides in DNA, and thereby inhibit carcinogenesis, chronic diseases, and aging.

Increased selenium intake in elderly high fish consumers may account for health benefits previously ascribed to omega-3 fatty acids

OBJECTIVE

To examine relationships between fish consumption and plasma selenium (Se) and red blood-cell fatty acid (RBC FA) profile in aged subjects. We hypothesised that the importance of Se has been underestimated when interpreting the beneficial effect of fish consumption on health.

DESIGN

Cross-sectional analysis of data from a prospective cohort study.

SETTING

The EVA study in Nantes, France (1991-2002).

SUBJECTS

200 subjects aged > or = 69 y with information on RBC FAs, plasma Se and completed food frequency questionnaires.

METHODS

We examined correlations between the most abundant FAs, Se and number of fish meals per week. Linear regression models were used.

RESULTS

Plasma Se was negatively correlated with RBC omega6 poly-unsaturated FA (PUFAs) and positively with omega3 PUFAs. Plasma Se, RBC omega3 PUFAs, docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA) increased with fish consumption. Conversely, levels of omega6 PUFAs were lower in the highest fish consumption group. All associations between plasma Se and fish consumption remained significant when adjusting for omega6 PUFAs alone or additionally for age, sex, education, diabetes, hypertension, dyslipidemia, cardiovascular diseases, and broad food categories (meat, eggs, dairy products, cereals, fruit and vegetable). Associations between omega3 PUFAs and fish also remained significant in the same model independently of Se. In linear regression models adjusted for demographic indicators, fish consumption explained only 2.6% of the variance in RBC omega3 FAs (6.2% for omega6) but as much as 15% of the variance in plasma selenium.

CONCLUSIONS

The observed health benefits of fish consumption in the elderly could be related not only to the increase in omega3 FA intake but also to other nutrients such as selenium. It is important to consider this observation when interpreting associations between fish consumption and health status in the elderly, particularly with regard to brain function.

Food-chain selenium and human health: spotlight on speciation

There is a growing appreciation that it is not just the total intake of dietary Se that is important to health but that the species of Se ingested may also be important. The present review attempts to catalogue what is known about Se species in foods and supplements and the health effects in which they are implicated. The biosynthetic pathways involved in Se assimilation by plants and the way in which Se species are metabolised in animals are presented in order to give an insight into the species likely to be present in plant and animal foods. Known data on the species of Se in the food chain and in food supplements are tabulated along with their concentrations and the analytical methodology used. The latter is important, since identification that is only based on retention-time matching with authentic standards must be considered as tentative: for evidence of structural confirmation, fragmentation of the molecular ion in addition to MS data is required. Bioavailability, as normally defined, is higher for organic Se species. Health effects, both beneficial and toxic, thought to be associated with specific Se species are described. Potent anti-tumour effects have been attributed to the low-molecular-weight species,Se-methyl-selenocysteine and its γ-glutamyl-derivative, found in a number of edible plants of theAlliumandBrassicafamilies. There remain considerable gaps in our knowledge of the forms of Se that naturally occur in foods. Without adequate knowledge of Se speciation, false conclusions may be drawn when assessing Se requirements for optimal health.

Selenium in food and the human body: a review

Selenium levels in soil generally reflect its presence in food and the Se levels in human populations. Se food content is influenced by geographical location, seasonal changes, protein content and food processing. Periodic monitoring of Se levels in soil and food is necessary. Diet is the major Se source and approximately 80% of dietary Se is absorbed depending on the type of food consumed. Se bioavailability varies according to the Se source and nutritional status of the subject, being significantly higher for organic forms of Se. Se supplements can be beneficial for subjects living in regions with very low environmental levels of Se. Several strategies have been followed: (1) employment of Se-enriched fertilizers; (2) supplementation of farm animals with Se; (3) consumption of multimicronutrient supplements with Se. Nevertheless, detailed investigations of possible interactions between Se supplements and other food components and their influence on Se bioavailability are needed. Suppliers also need to provide more information on the specific type of Se used in supplements. In addition, research is lacking on the mechanisms through which Se is involved in hepatocyte damage during hepatopathies. Although Se potential as an antioxidant for the prevention of cardiovascular diseases (CVD) is promising, additional long-term intervention trials are necessary. As a result, indiscriminate Se supplements cannot be reliably recommended for the prevention of CVD in human beings. Some interesting findings reported an association of Se intake with a reduced prevalence and risk for prostate and colon cancer. However, random trials for other cancer types are inconclusive. As a final conclusion, the general population should be warned against the employment of Se supplements for prevention of hepatopathies, cardiovascular or cancer diseases, because benefits of Se supplementation are still uncertain, and their indiscriminate use could generate an increased risk of Se toxicity.

Bioaccumulation potential of dietary arsenic, cadmium, lead, mercury, and selenium in organs and tissues of rainbow trout (Oncorhyncus mykiss) as a function of fish growth

The distribution and potential bioaccumulation of dietary arsenic, cadmium, lead, mercury, and selenium in organs and tissues of rainbow trout (Oncorhyncus mykiss Walbaum, 1792), a major aquaculture species, was studied in relation to fish growth over a period of >3 years. Fish were reared under normal farming conditions, that is, fed a standard fish food and exposed to negligible levels of waterborne trace elements. The age-related variations in the content of each trace element in gills, kidney, liver, muscle, and skin were studied through nonparametric regression analysis. A buildup of all elements in all tissues and organs was observed, but due to dilution with growth, the concentrations did not increase, except in a few cases such as cadmium and mercury in liver and kidney. In muscle tissue, the concentrations of mercury, lead, and selenium did not alter significantly with growth, whereas cadmium increased but remained at exceedingly low levels. The concentration of arsenic in muscle tissue peaked at 14 months and then decreased in adult specimens. Arsenic speciation by high-performance liquid chromatography--inductively coupled plasma mass spectrometry revealed that arsenic in muscle was almost exclusively present in the form of nontoxic arsenobetaine. Application of a mercury mass balance model gave predicted concentrations in agreement with measured ones and showed that in farmed rainbow trout the ratio of mercury concentrations in feed and in fish is about 1:1. Therefore, rainbow trout does not approach the limits established for human consumption even when reared with feed at the maximum permitted levels. These findings highlight the low bioaccumulation potential of toxic trace elements such as cadmium, lead, and mercury in rainbow trout following dietary exposure. On the other hand, selenium concentrations in muscle (about 0.2 microg g (-1) of fresh weight) show that rainbow trout may be a good source of this essential element.

Selenium speciation and bioavailability in biofortified products using species-unspecific isotope dilution and reverse phase ion pairing-inductively coupled plasma-mass spectrometry

In some regions of the world, where the bioavailability of selenium (Se) in soil is low and/or declining (e.g., due to use of high-sulfur fertilizers), there is increased risk of adverse affects on animals and human health. In recent years, increased research attention has focused on understanding the relationships between Se contents in foods and supplements and their nutritional benefits for animal and humans. The objective of this study was to use a species-unspecific isotope dilution and reverse phase ion pairing-inductively coupled plasma-mass spectrometry techniques for the identification and quantification of Se species in biofortified grains (i.e., wheat and triticale), flour, and wheat biscuits. The information on Se species was used to gain an understanding of the bioavailability of Se in biofortified and process-fortified wheat biscuits used in a clinical trail. The major Se species identified in biofortified and process-fortified samples were selenomethionine (76-85%) and selenomethionine selenoxide (51-60%), respectively. Total plasma Se concentrations in the biofortified Se exposure group were found to increase throughout the 6 month trial period (mean=122 microg L(-1) at 0 months to 194 microg L(-1) at 6 months). In contrast, the trial group exposed to process-fortified Se biscuits showed little increase in mean total Se plasma concentrations until 4 months of exposure (mean=122 microg L(-1) at 0 months to 140 microg L(-1) at 4 months) that remained constant until the end of the trial period (mean=140 microg L(-1) at 4 months to 138 microg L(-1) at 6 months). The difference in total Se plasma concentrations may be due to the presence and bioavailability of different Se species in biofortified and process-fortified biscuits. An understanding of Se speciation in foods enables better understanding of pathways and their potential benefits for animals and humans.

Brazil nuts: an effective way to improve selenium status

BACKGROUND

Brazil nuts provide a rich natural source of selenium, yet no studies have investigated the bioavailability of selenium in humans.

OBJECTIVE

We investigated the efficacy of Brazil nuts in increasing selenium status in comparison with selenomethionine.

DESIGN

A randomized controlled trial was conducted with 59 New Zealand adults. Participants consumed 2 Brazil nuts thought to provide approximately 100 mug Se, 100 mug Se as selenomethionine, or placebo daily for 12 wk. Actual intake from nuts averaged 53 mug Se/d (possible range: 20-84 mug Se). Plasma selenium and plasma and whole blood glutathione peroxidase (GPx) activities were measured at baseline and at 2, 4, 8, and 12 wk, and effects of treatments were compared.

RESULTS

Plasma selenium increased by 64.2%, 61.0%, and 7.6%; plasma GPx by 8.3%, 3.4%, and -1.2%; and whole blood GPx by 13.2%, 5.3%, and 1.9% in the Brazil nut, selenomethionine, and placebo groups, respectively. Change over time at 12 wk in plasma selenium (P < 0.0001 for both groups) and plasma GPx activity in the Brazil nut (P < 0.001) and selenomethionine (P = 0.014) groups differed significantly from the placebo group but not from each other. The change in whole blood GPx activity was greater in the Brazil nut group than in the placebo (P = 0.002) and selenomethionine (P = 0.032) groups.

CONCLUSION

Consumption of 2 Brazil nuts daily is as effective for increasing selenium status and enhancing GPx activity as 100 mug Se as selenomethionine. Inclusion of this high-selenium food in the diet could avoid the need for fortification or supplements to improve the selenium status of New Zealanders.