Determination of selenium in serum by FI-HG-AAS and calculation of dietary intake

A method was developed for the determination of selenium concentration in serum by flow injection-hydride generation-atomic absorption spectrometry (FI-HG-AAS) following microwave digestion of serum samples and reduction of selenate to selenite. The detection limit of the method was 0.3 μg Se/L and the characteristic concentration, corresponding to the 0.0044 absorbance signal, was 0.12 μg Se/L. The results from the analysis of two Seronorm standard reference materials showed good agreement with the certified values. The method was then used to analyze selenium in sera of Austrian and Slovenian people for the calculation of dietary intakes. The selenium concentrations in sera of mothers at delivery, their neonates, and the male and female adults were 71 ± 14, 42 ± 6, 75 ± 21, and 65 ± 16 μg/L for the Austrians and 62 ± 15, 34 ± 7, 70 ± 12, and 66 ± 15 μg/L for the Slovenians. The dietary intakes of selenium of the mothers and the male and the female adults were calculated as 52, 37, and 46 μg/d for the Austrians and 45, 38, and 32 μg/d for the Slovenians.     

广州市食物硒含量及居民硒摄入量

调查了广州市常见食物中的硒含量.结果表明:动物性食品内脏、水产品、蛋类和羊肉等食品中的硒含量最为丰富(>150.0μg.kg-1);谷物与豆类中的硒含量相近(46.5～98.3μg.kg-1);蔬菜(15.8μg.kg-1)和水果(4.97μg.kg-1)中硒含量均较低;菌类在植物性食品中的硒含量最高(46.0μg.kg-1).广州市居民硒摄入量为98.5μg.d-1.其中,动物性食品占总硒摄入量的73.7%;植物性食品占26.3%;水产品和猪肉均占22.0%以上;大米占17.2%.广州市食品中的硒含量和居民每日硒摄入量能满足人体生理需要.     

Revised reference values for selenium intake

The German, Austrian and Swiss nutrition societies are the joint editors of the ‘reference values for nutrient intake’. They have revised the reference values for the intake of selenium and published them in February 2015. The saturation of selenoprotein P (SePP) in plasma is used as a criterion for the derivation of reference values for selenium intake in adults. For persons from selenium-deficient regions (China) SePP saturation was achieved with a daily intake of 49 μg of selenium. When using the reference body weights the D-A-CH reference values are based upon, the resulting estimated value for selenium intake is 70 μg/day for men and 60 μg/day for women. The estimated value for selenium intake for children and adolescents is extrapolated using the estimated value for adults in relation to body weight. For infants aged 0 to under 4 months the estimated value of 10 μg/day was derived from the basis of selenium intake via breast milk. For infants aged 4 to under 12 months this estimated value was used and taking into account the differences regarding body weight an estimated value of 15 μg/day was derived. For lactating women compared to non-lactating women a higher reference value of 75 μg/day is indicated due to the release of selenium with breast milk. The additional selenium requirement for pregnant women is negligible, so that no increased reference value is indicated.     

Dietary intake of selenium and its concentration in breast milk

Selenium concentration was measured in the breast milk of 30 mothers at different stages of lactation and various body mass indices (BMI). For a maternal mean selenium intake meeting 100% of the Recommended Daily Allowance, mean milk selenium concentration was 14.06 ng/mL (range: 10.0–24.7 ng/mL). No significant correlation was found between the concentration of milk selenium with the stage of lactation, BMI, or dietary selenium intake.     

Factors affecting the selenium intake of people in transbaikalian Russia

The selenium concentration in foods grown and consumed and in plasma, red blood cells, and toenails of people living in the district of Chita in the transbaikalian part of Russia were studied in August 1991. Preliminary results from the area have suggested low selenium intakes and the possible occurrence of cardiomyopathy (Keshan disease) in the population. A low selenium concentration in foods grown locally was found: mean selenium concentration in wheat grains was 1, 5, and 28 μg/kg, respectively, in three villages studied, that of oats was beween 3–6 μg/kg, and of cow's milk 10–27 μg/kg dry matter. The selenium concentration of bread was considerably higher, between 87–337 μg/kg dry wt, presumably because wheat imported from the US had been used for baking. Occasional samples of pork, beef, and mutton contained between 32–318 μg selenium/kg dry wt. Low selenium concentrations were observed in samples of soil and river water. The mean plasma selenium concentration of 52 persons was 1.02 μmol/L, including 33 children and 19 adult subjects. The selenium concentrations in red blood cells and toenails were 1.95 μmol/L and 0.61 mg/kg, respectively. No symptoms of heart disease caused by selenium deficiency were observed. It is concluded that the selenium status of people was fairly good thanks to the contribution to dietary intake of imported wheat with a high selenium content. As the selenium concentration was very low in foods grown in the area, the selenium intake of the population will be reduced to a very low level if only locally produced foods are consumed.     

Bioavailability and possible benefits of wheat intake naturally enriched with selenium and its products

Bioavailability and possible benefits of wheat intake naturally enriched with selenium and its products was tested. Wheat obtained by application of an original combination and procedure for foliar supplementation of plants with Se was characterized on the average by five times higher content of Se, the main form being l-(+)-selenomethionine (SeMet). Substitution of Se-deficient wheat by wheat naturally enriched with Se and its products contributed to the increase of daily intake on the average by 18 μg (12–35 μg) in volunteers, which is more than 50% of the average daily intake. Six weeks after the beginning of its application, increased daily intake of Se brought about the increase of its concentration in the plasma of the examined persons by 53%, in their erythrocytes by 37%, in their hair by 44%, and in their urine by 54%. This result was comparable to the effect obtained in the course of an 8-wk daily intake of supplements with 100 μg Se in the form of enriched bakery yeast. Analysis of glutathione peroxidase (GSH-Px) activity in blood, thiobarbituric acid reactive substances (TBARS) in plasma, lipid parameters (total cholesterol, high-density lipoprotein cholesterol, low-density lipoprotein cholesterol, and triglycerides), and glucose in serum of volunteers showed that the increased Se intake induced increased GSH-Px activity in blood and decreased concentrations of TBARS, lipid parameters, and glucose in blood. Using only one crop (wheat enriched with Se), the existing deficiency of Se in our population can be alleviated. In this way, one-fourth of our population with lower Se intake than 21 μg/d will satisfy basal requirements, whereas one-half will become moderately deficient in Se instead of distinctly deficient in Se.     

CCK-octapeptide injected in CSF decreases meal size and daily food intake in sheep

Cholecystokinin octapeptide (CCK-OP) is a potent and specific suppressor of feeding when administered as a continuous lateral cerebral ventricular injection in fasted sheep, and we have proposed that endogenous CCK-OP in the brain is released during meals and acts to terminate feeding. In previous studies, however, only relatively short-term effects of CCK-OP on feeding were examined. In the first experiment of the present series sheep were adapted to a 6-hr feeding period per day. CCK-OP injected continuously for 6 hr into the lateral ventricles reduced feeding during the entire feeding period (809 ± 72 g, sham; 695 ± 71 g, carrier; 505 ± 69 g, CCK-OP; p<0.05). In addition mean feed intake for the two days (injection + first post injection day) was significantly reduced by CCK-OP; thus with CCK-OP, sheep did not compensate by the day after injection for the decreased feed intake on injection day. In a second experiment CCK-OP was injected into the lateral ventricles only during four consecutive 15 min meals 2 hours apart. With a dose of 0.159 pmoles/min CCK-OP, size of the second meal was reduced, but with 0.638 pmoles/min CCK-OP feeding during each of the first two meals was reduced and cumulative intake for the four meals was decreased. These results indicate that CCK-OP administered centrally can have long-term effects on feeding, and under appropriate conditions, could result in negative energy balance.     

Platelet selenium in children with normal and low selenium intake

The concentration of selenium was determined by instrumental neutron activation analysis in erythrocytes, platelets, and plasma of eight dietetically treated children with phenylketonuria (n=6) or maple-syrup-urine disease (n=2) with low selenium intake and for ten children with normal selenium intake. The normal selenium concentration in platelets was about 600 ng/g and about five times higher than in erythrocytes of the same children. A decreased selenium concentration in platelets was seen only when the corresponding concentrations in erythrocytes and plasma were very low. This suggests a special role of selenium in platelets.     

Determination of selenium in Libyan food items using pseudocyclic instrumental neutron activation analysis

Cyclic and pseudocyclic instrumental neutron activation analysis (INAA) has been used to determine the Se content of 40 Libyan food items. The selected samples include different varieties of local and imported foods such as wheat and barley products (bran and flours), rice, bread, almond, peanuts, vegetables as bean and peas, tea, coffee, sugar, and commonly used spices such as red and black paper, curry, cumin, mixture of spices, thyme, coriander, and fenugreek. Both conventional and anticoincidence γ-ray spectrometry techniques have been employed. Pseudocyclic INAA in conjunction with anticoincidence counting has been found to provide the most reliable results. The precision of the method has been significantly improved by recycling the samples up to three times. The accuracy has been evaluated by analyzing a number of certified reference materials of varied Se levels. The detection limit has been found to vary between 26 and 90 ppb Se depending on the sample composition. The range of daily dietary intake has been calculated as 13–44 μg of Se per day.     

The selenium intake of the female chicken influences the selenium status of her progeny

The primary purpose of this study is to determine the extent to which the effects of dietary supplementation of the female chicken with selenium (Se) continue into the next generation. An additional aim is to compare the relative effectiveness of pre-hatch (from the hen's diet) with that of post-hatch (from the progeny's diet) supplementation with Se on the Se status of the chick during the first 4 weeks of post-hatch life. Hens were maintained on control or Se-supplemented diets, respectively containing 0.027 and 0.419 μg Se/g of feed. The high-Se diet elevated the Se content of the hens' eggs by 7.1-fold. At hatch, the concentrations of Se in the liver, breast muscle and whole blood of the chicks originating from the high-Se parents were, respectively, 5.4-, 4.3- and 7.7-fold higher than the values in the chicks of the low-Se parents. When the offspring from the two parental groups were both maintained on the low-Se progeny diet, the tissue Se concentrations in chicks originating from the high-Se hens remained significantly higher for 3–4 weeks after hatching, compared with the values in chicks from the low-Se hens. Similarly, tissue glutathione peroxidase activity remained significantly higher in chicks from the high-Se hens for 2–4 weeks post-hatch. Thus, the effects of maternal Se supplementation persist in the progeny for several weeks after hatching. However, when chicks hatching from low-Se eggs were placed on a high Se diet, their tissue Se concentrations at 7 days of age were markedly higher than the values in chicks from high-Se eggs placed on the low-Se diet.     

Studies on the relations of selenium and Keshan disease

Keshan disease is an endemic cardiomyopathy of unknown cause in The People’s Republic of China that occurs most frequently in children under 15 years of age and women of child-bearing age. Studies of children 1–9 years old in Mianing County of Sichuan Province have indicated that Keshan disease is a selenium responsive condition. Incidence rates of 9.5–13.5/1000 in 1974–1975 were reduced to 1–2/1000 in children treated with a tablet weekly of 0.5–1 mg sodium selenite. During 1974–1977, only 21 cases of the disease occurred in 36,603 treated children, compared with 106 cases in 9430 untreated children, of whom 53 died and 5 still have insufficient heart function. Occurrence of the disease was invariably associated with a lower selenium content of cereals, and of hair (less than 0.12 ppm Se) in residents from affected, compared with non-affected, areas. The dose relationship between selenium and regional characteristics of Keshan disease suggests that it is probably a biogeochemical disease; other etiological factors have also been considered.     

Plasma and liver selenium levels in the rat during supplementation with 0.5, 2, 6, and 15 ppm selenium in drinking water

Plasma and liver selenium of Wistar rats were determined after 1, 3, and 6 mo supplementation with 0.5, 2, 6, or 15 ppm selenium as sodium selenite in drinking water. Plasma selenium was not different from control values at additional intake of 0.5 ppm but increased above usual levels at higher intakes. A highly significant correlation was observed between the total quantity of selenium ingested and plasma selenium after 1 mo treatment (r=0.99,p<0.01), but was less pronounced after 3 and 6 mo (0.94,p<0.05, and 0.78,p<0.05, respectively). The decrease in plasma selenium with time of treatment was more pronounced at higher intakes. There was also a highly significant correlation between total selenium intake and liver selenium concentration (r=0.99,p<0.01) after 1 mo of treatment, but this time liver selenium did not change with time, and the correlation remained highly significant throughout the investigation. Liver selenium therefore appears as a more sensitive and more representative measure of selenium intake than plasma selenium. Most supplements did not affect body weight and survival of animals, except when the diet was supplemented with 15 ppm for 6 mo; however, alterations in biochemical parameters concerning lipid status and hepatic function were observed at levels above 2.0 ppm.     

Dietary selenium intake of chinese adult women in the 1990s

To assess the levels of daily dietary intake of selenium (Se) among the general Chinese population, a series of field surveys were conducted in the 1990s. Samples of 24-h duplicates of foods were collected from 500 participants (300 in 6 cites and 200 from 4 villages). Se levels were determined by microwave digestion followed by inductively coupled plasma-mass spectrometry (ICP-MS), and the measurements were compared with FCT (Food Composition Tables)-based estimates. The average daily intake of Se was 69.2 μg/d (79.9 and 53.1 μg/d in urban and rural areas, respectively) by instrumental determination and 35.1 μg/d (36.7 and 32.7 μg/d) by FCT-based estimation. As the distribution of Se should be uneven within China, the FCT-based estimation is of a limited value and the ICP-MS determination of Se is more accurate and reliable when evaluating the nutritional status of local people. Taking ICP-MS-based values, Se intakes were lower in rural areas than in urban areas, and the intakes of about half of the people in rural areas were less than the Recommended Daily Allowance (RDA) in China of 50 μg/d. The low intake might be resulted from difference in the types of food consumed. Thus, the dietary intake of Se basically meets the recommended RDA in most of urban areas, but insufficiency may be still a nutritional and public health problem in some rural areas.     

The daily dietary selenium intake of West German adults

The selenium content of food consumed in the Federal Republic of Germany (FRG) was determined for the estimation of the dietary selenium intake of West German adults. The daily dietary selenium intake of men is 47 micrograms (micrograms) and that of women 38 micrograms, corresponding to 0.67 microgram/kg body weight per day for both men and women. Animal protein is the main source of dietary selenium, accounting for 65.5% of the total selenium intake. Pork contributes 25.1% to the total Se intake, reflecting the current consumption and the selenium supplementation of feedstock rather than the availability of selenium from natural dietary sources. The selenium intake of adults in West Germany is only slightly higher than in New Zealand, Finland, and Italy, nearly equal to that in Belgium and France, and distinctly lower than in Great Britain, the USA, Canada, and Japan.     

Effect of supplementation with selenium on whole blood glutathione peroxidase activities and on plasma and tissue selenium concentrations in lambs

In recent years the selenium (Se) intake of the human population of the UK has shown a marked decline from 60 μg/d in 1978 to around 30 μg/d in 1990 owing largely to a significant reduction in the importation of North American wheat for bread-making fluor. Other countries (Finland, for example) in similar situations have instituted fertilization programs in order to raise cereal Se concentrations and thus boost dietary intakes. An alternative approach would be to increase the Se concentration of carcass meat by supplementation of meat animals for a limited period prior to slaughter. A trial was set up with store lambs to evaluate this approach. Sixteen Scottish Blackface lambs were stratified according to live weight and then randomly allocated to one of four treatments: unsupplemented, or 3.5, 7, or 10.5 mg. Se/head/wk. After 14 wk, the lambs were sacrificed and samples of shoulder and thigh muscle, liver, and kidney were obtained for analysis. All three treatments effected an increase in whole blood glutathione peroxidase (GSH-Px) and plasma Se concentrations over controls. Shoulder, thigh, and liver Se exhibited a dose-response relationship to treatment, but kidney Se concentrations were unaffected by treatment. Muscle and some organ meat Se concentrations can therefore be increased by supplementation and could contribute to increased human dietary intakes of the element.     

Evaluation of dry matter intake and daily weight gain predictions of the Cornell Net Carbohydrate and Protein System with local breeds of beef cattle in China

Three feeding trials with different dietary treatments were conducted to evaluate predictions of dry matter intake and average daily gain of Chinese local beef cattle by Cornell Net Carbohydrate and Protein System (CNCPS) version 5.0. In Trial 1, 60 growing Jin Nan yellow steers (local yellow cattle breed originated from Shanxi Province) were assigned to two treatments with five pens in each treatment and six animals in each pen. Trial 2 was conducted with 72 Lu Xi yellow growing steers (local yellow cattle breed originated from Shandong Province) in 12 conventional pens. These animals were assigned to four treatments with six animals in each pen. In Trial 3, 60 Lu Xi yellow steers were allocated to four treatments with five animals in each pen. Average daily dry matter intake (DMI) for each steer was measured as a mean of each pen. All the data about animals, environment, management and feeds required by the CNCPS model were collected, and model predictions were generated for animals of each pen. Model predictions were evaluated by mean bias, mean square prediction error (MSPE) and regression between the observed and predicted values. Animals in 9 of 10 treatments showed a very close model-predicted DMI values to the observed. In another treatment, animals had a mean bias of −0.72 kg DM/day (TRT 10 in Trial 3). With overall data included, the regression equation between observed and predicted DMI was: Y_OBS = 1.10X_CNCPS − 0.78 (R² = 0.82; P<0.0001), with an intercept not different (P=0.32) from zero, but a slope still different (P<0.0001) from 1. Although the model-predicted ADG values were very close to the observed values in all trials, most of the predicted values were always lower than the observed values with absolute mean bias less than 0.2. When all data were pooled, the regression equation between observed and predicted ADG was: Y_OBS = 1.07X_CNCPS + 0.02 (R² = 0.73; P<0.0001), with an intercept not different from zero (P=0.88), but a slope that differed from unity (P<0.0001). Results suggest that the CNCPS model is an acceptable model to predict dietary DM intake and average daily gain of Chinese local beef cattle breeds. Further studies are warranted to introduce model adjustment for Chinese conditions.     

Effects of nationwide addition of selenium to fertilizers on foods,and animal and human health in Finland: From deficiency to optimal selenium status of the population

Despite different geological features the Nordic countries are generally selenium-poor areas. In each country various factors such as food importation and life-style determine the selenium (Se) intake. Due to an extremely low Se intake in the 1970s in Finland, 0.025 mg/day, an official decision was made in 1984 to supplement multinutrient fertilizers with Se in the chemical form of sodium selenate. Almost all fertilizers used in Finland since 1985 have contained Se. Currently all crop fertilizers contain 15 mg Se/kg. Finland is still the only country to take this country-wide measure.In a national monitoring programme, sampling of cereals, basic foodstuffs, feeds, fertilizers, soils, and human tissues has been carried out annually since 1985 by four governmental research organizations. Sampling of foods has been done four times per year and human blood has been obtained annually from the same (n = 60) adults. The accuracy of analyses has been verified by annual interlaboratory quality control. During this programme the selenium concentration of spring cereals has increased on average 15-fold compared with the level before the Se fertilization. The mean increase in the Se concentration in beef, pork and milk was 6-, 2- and 3-fold. In terms of Se, organically grown foods of plant origin are generally comparable to products produced before the Se supplementation of fertilizers. Milk from organically fed cows is 50% lower in Se than the usual milk. The average dietary human intake increased from 0.04 mg Se/day/10 MJ in 1985 to a present plateau of 0.08 mg Se/day/10 MJ, which is well above the current nutrition recommendations. Foods of animal origin contribute over 70% of the total daily Se intake. The mean human plasma Se concentration increased from 0.89 μmol/L to a general level of 1.40 μmol/L that can be considered to be an optimal status. The absence of Se deficiency diseases and a reference population have made conclusions on the impact on human health difficult. However, the rates of cardiovascular diseases and cancers have remained similar during the pre- and post-supplementation indicating medical and life-style factors to be much stronger determinants than Se. The nationwide supplementation of fertilizers with sodium selenate is shown to be effective and safe in increasing the Se intake of the whole population. Also, the health of animals has improved.     

Determination of selenium and its compounds in marine organisms

In this study, we investigate the type and quantity of selenium compounds in fish and marine organisms, using ion-pair reversed phase LC–ICP-MS, developed and applied for the analysis of Atlantic cod, Atlantic salmon, Greenland halibut, Atlantic herring, blue mussel, common crab, scallop, calanus, and Euphasia super. Of the samples examined, the lowest level of selenium was found in farmed Atlantic salmon (0.17 mg Se kg⁻¹ dm). The total selenium extraction efficiency by phosphate buffer was 2.5 times higher in sea plankton and shellfish samples than in fish samples. Analysis of Se species in each hydrolysate obtained by proteolysis showed the presence of selenomethionine, which constituted 41.5% of the selenium compounds detected in hydrolysates of Atlantic herring and 98.4% of those in extracts of Atlantic salmon. Inorganic compounds, such as selenates and selenites, were detected mainly in sea plankton and shellfish samples (<0.13 mg Se kg⁻¹ wm), although no correlation was found between the presence of inorganic compounds and total selenium concentration. The accuracy of the total selenium determination was validated using a certified reference material (oyster tissue (NIST 1566b)). A lyophilised powder of cod (Gadus morhua) was used to validate speciation analysis, enzymatic hydrolysis of lyophilised powder of cod recovered 54 ± 6% of total selenium, and SeMet constituted 83.5 ± 5.28% of selenium detected in hydrolysates. The chromatographic detection limits were, respectively, 0.30 ng mL⁻¹, 0.43 ng mL⁻¹, 0.54 ng mL⁻¹, 0.55 ng mL⁻¹, 0.57 ng mL⁻¹ and 0.72 ng mL⁻¹ for selenate, selenomethionine, selenite, Se-methyl-selenocysteine, selenocystine and selenomethionine selenoxide.The data on selenium concentrations and speciation presented here could be useful in estimating levels of selenium intake by seafood consumption.     

A tentative recommendation for the maximum daily intake of selenium.

In order to make a tentative recommendation for the maximum acceptable daily intake of selenium, relevant data were compiled from the available literature. Normal daily intake of selenium from foods was estimated as about 100 mug, half of which comes from fish and shellfish (in an average adult Japanese). Intake of selenium from other sources was negligible. The amount of selenium excreted in the urine was found to be compatible with the estimated value of the daily oral intake. The range of the margin of safety was then estimated as 10 to 200 times the normal level on the basis of human and animal toxicity data. The variation of dietary selenium intake in the general population is discussed, leading to the conclusion that the consumers of large amounts of fish may ingest as much as 500 mug daily. Consequently, a value of 500 mug is proposed as the tentative maximum acceptable daily intake of selenium for the protection of human health.     

Determination of selenium stable isotopes by gas chromatography–mass spectrometry with negative chemical ionisation

A gas chromatography mass spectrometric method using negative chemical ionisation was developed for the determination of stable isotopes of selenium for evaluation of selenium absorption and retention from foods in humans. The method involves an acid digestion to convert all selenium into selenite, which subsequently reacts with 4-nitro-o-phenylene-diamine to form a volatile piazselenole. The piazselenole, after extraction into an organic solvent, was analysed for its isotopic selenium composition by gas chromatography mass spectrometry. Negative chemical ionisation is reported for the first time for the determination of selenium stable isotopes and its analytical characteristics were compared to those of electron impact mass spectrometric ionisation, classically used for the determination of selenium. The negative chemical ionisation technique allowed accurate determination of total selenium by isotope dilution and of selenium isotope ratios in biological samples. The repeatability for total selenium and for stable isotope ratios was good (R.S.D.≤10%) within the range of 50 to 250 ng selenium. The detection limit for the investigated selenium isotopes was approximately 1 pg (signal to noise ratio at 3). The applicability of the developed stable isotope methodology was demonstrated by the determination of the selenium absorption and retention from foods in a pilot study using one human adult.