Selenium in human urine: concentration levels and medical implications.

Selenium concentration values for human urine samples are presented, and the literature on the chemical species of the element in urine is critically reviewed. Daily excretion levels in healthy persons and in pathological or experimental conditions are compiled. Medical implications and the significance of urinary selenium determination in assessing the selenium status in man are discussed.

Effect of thickening agents, based on soluble dietary fiber, on the availability of calcium, iron, and zinc from infant formulas.

Although it is accepted that dietary fiber probably is not needed in the diets of infants younger than 1 y, babies suffering from regurgitation are often fed with infant formulas thickened with considerable amounts of fiber. The effect of increasing amounts of alginic acid, locust-bean gum, and guar gum was studied from casein and whey-based infant formulas. A dialysis in vitro method with preliminary intraluminal digestion, adapted to the conditions of infants younger than 6 mo, was used. Human milk was used as the reference standard. Elemental contents of samples and dialysates were determined by atomic absorption spectrometry. Soluble dietary fiber inhibited mineral availability more in casein than in whey-based formulas. Mineral availabilities from casein- and whey-based formulas supplemented with 0.42 g of locust-bean gum/100 mL were 9.4% (0.7) and 10.4% (0.6) for calcium (P < 0.05), 0.32% (0.08) and 1.45% (0.17) for iron (P < 0.05), and 3.2% (0.2) and 5.6% (0.5) for zinc (P < 0.05), respectively. Calcium availability from the whey formula decreased in the presence of each fiber source, especially guar gum and alginic acid. Supplementing 2 g of alginic acid-based agents per 100 mL depressed calcium availability from 13.3% (1.2) to 5.3% (0.3; P < 0.05). With respect to iron and zinc, availabilities increased from 1.28% (0.28) to 6.05% (0.96; P < 0.05) and from 6.7% (0.6) to 10.2% (1.0), respectively, with the addition of 2 g of alginic acid (P < 0.05). Both gums lowered iron and zinc availabilities, and guar gum affected iron availability more severely than locust-bean gum did. Iron availabilities were 1.45% (0.17) from formula thickened with locust-bean gum (0.42 g/100 mL) and 0.92% (0.15) from formula thickened with guar gum (P < 0.05). Adding thickening agents based on soluble dietary fiber to traditional infant formulas probably affects calcium, iron, and zinc availability in various ways.

Selenium in human urine determination, speciation and concentration levels.

Procedures for determination of selenium in urine samples are reviewed. Basic problems encountered in sampling and sample-treatment are discussed. Concentration levels and spedation of the element are summarized.

The determination of selenium by atomic-absorption spectrometry: A review.

A comprehensive review is given of the determination of selenium by the various atomic-absorption spectrometry methods that have been developed, covering the use of various flame and electrothermal ionization methods, hydride techniques, preconcentration and separation, and giving an appraisal of the results.

Optimization of the determination of selenium by atomic-absorption spectrometry: Comparison of two hydride generation systems.

Two commercially available systems for the determination of selenium by hydride-generation and atomic-absorption spectrometry were compared. Chemical and physical parameters were optimized both for an electrothermally heated closed atom-cell method and a flame-heated open-cell technique. Both systems were evaluated with respect to performance and applicability to determination of traces of selenium.

The selectivity of a macrotetrolide electrode towards organic onium ions.

The selectivity for ammonium and some of its alkyl derivatives has been experimentally determined for a liquid-membrane ammonium electrode.

Losses of metabolically incorporated selenium in common digestion procedures for biological material.

Two common procedures for wet destruction of biological materials for subsequent determination of selenium have been investigated. Rat organs and biological fluids were endogenously labelled with (75)Se to monitor losses during the procedures. Addition of nitric and perchloric acids with gradual heating up to 210 degrees seemed to be the best method: at this temperature the labelled selenium was still recovered quantitatively, and the destruction was fast and efficient.

Daily dietary intake of manganese by several population groups in Belgium: preliminary reports.

Atomic absorption spectrometry is used to determine manganese content of several duplicate meals consumed by different population groups in the Antwerp region (Belgium). Daily elemental intake, beverages not included, is calculated and proven to be within the recommended daily allowances (National Academy of Sciences, USA) except for a higher intake by macrobiotics (6.7 +/- 3.8 mg per day). Intake level of vegetarians is similar to that of omnivorous adults, 2.9 +/- 2.0 and 2.5 +/- 0.3 mg per day, respectively. Values obtained in this study are compared with scarce data on intake by similar groups in other countries.

Trace elements in human milk, selenium a case study.

Longitudinal changes of the trace element (Fe, Cu, Zn, Mn, Mo, Cr, Co, As, Se) composition of human milk are discussed. The mean daily intake of breast fed infants is compared with the intake of infants fed cow's milk and with recommended dietary allowances. Parameters which can be used to check the selenium status are discussed. Clinical consequences of selenium deficiency are discussed.

Atomic absorption spectrometric determination of zinc, copper, and selenium in fish from Lake Tanganyika, Burundi, Africa.

Atomic absorption spectrometric determination of zinc, copper and selenium in fish from Lake Tanganyika (Burundi) shows that, although this lake is not polluted, trace element intake by fish contributes an important part of the elemental intake by man. No correlations were found between trace element levels in the fish and fish lipid and protein content. Copper and zinc were positively and highly correlated (P less than 0.005). Interspecies comparison for trace element content of fish samples is discussed. Unless the level of water pollution is taken into account, intraspecies variation cannot be evaluated.

Zinc, copper, and selenium in milk and organs of cow and goat from Burundi, Africa.

Atomic absorption spectrometric determination of zinc, copper and selenium in milk from cow and goat from Burundi provide values, which agree quite well with literature data. Muscle from both animals is a rich source of zinc, but not for copper and selenium. Liver accumulates the highest amount of copper, while for selenium the kidney is the target organ.

Daily dietary intake of copper, zinc and selenium by different population groups in Burundi, Africa.

Daily dietary intake of copper, zinc and selenium for different population groups in Burundi, Africa, has been determined, using different sampling strategies, by atomic absorption spectrometry. Recommended daily intakes (RDA, National Academy, USA) are met for copper and zinc. For selenium, especially the rural population risk a deficiency as observed with a daily intake of 17 micrograms. The importance of different types of food in daily intake is discussed. Legumes proved to be an important source of copper, while for selenium fish contributes in a large part in dietary intake. Calculated total daily intakes are compared with intakes recently published for other countries.

Copper, zinc, manganese, iron, lead, cadmium, mercury and arsenic in fish from Lake Tanganyika, Burundi.

Atomic absorption spectrometric determination of copper, zinc, manganese, iron, lead, cadmium, mercury and arsenic in two fish species from Lake Tanganyika, Burundi, provide values that are lower than most literature data, especially for cadmium, arsenic and mercury. Tissue analysis of Lates stapersii reveals that liver accumulates the highest amount of most elements. The data illustrates that Lake Tanganyika is still a non-polluted area at the time of analysis.

Selenium in environmental and drinking waters of Belgium.

The tetravalent and hexavalent selenium content of water samples can be determined by conventional energy-dispersive X-ray fluorescence after different preconcentration steps. Selenium values of nearly three-hundred different environmental and drinking water samples in Belgium are reported. The results are quite low, ranging from the detection limits up to 1 microgram 1-1. The concentration levels are compared to literature data and the speciation is discussed. The contribution of drinking water to the daily intake of selenium in Belgium ranges from less than 0.2 to 5%.

Daily dietary intake of copper, zinc, and selenium of exclusively breast-fed infants of middle-class women in Burundi, Africa.

Copper (Cu), zinc (Zn), and selenium (Se) in human milk of middle-class Burundian women during the first 10 mo of lactation have been determined. Wet acid digestion, using nitric and perchloric acids, and atomic absorption spectrometric analysis have been used. Daily intakes have been calculated and proven to decrease from 0.39 +/- 0.05 (colostrum) to 0.16 +/- 0.02 (mature milk), 2.3 +/- 0.3 (colostrum), to 1.2 +/- 0.2 mg (mature milk) and 10.9 +/- 1.5 (colostrum) to 5.3 +/- 0.8 micrograms (mature milk) for Cu, Zn, and Se, respectively. Since values for this African country are nonexistent, intake levels are compared with literature data and found to be somewhat higher than those observed in other poorly nourished countries. The recommended safe and adequate daily intake for infants of 0-6 mo of age, as proposed by the National Research Council of the USA, is only met for Burundian infants < 1 mo of age. The function of copper (Cu) and zinc (Zn) as essential trace elements has been known for quite a number of years (1). Also, selenium (Se) is a trace element essential for the activity of glutathione peroxidase (2) and type I iodothyronine 5-deiodinase (3). For all three elements, an adequate intake is necessary for satisfactory infant growth and development (4). In view of the almost total lack of relevant data on Burundi (Africa), we have determined Cu, Zn, and Se in human milk of middle-class Burundian women during the first 10 mo of lactation (5). The aim of this study is to assess infants' elemental intake for this country and compare this with literature data on trace elemental intake of exclusively breast-fed infants.

PIP: Copper and zinc are essential trace elements in the human diet, while selenium is a trace element essential for the activity of glutathione peroxidase and type I iodothyronine 5-deiodinase. Infants need to consume enough of each of these elements in order to grow and develop satisfactorily. The authors investigated the levels of copper, zinc, and selenium in human milk of middle-class Burundian women during the first ten months of lactation. Wet acid digestion, nitric and perchloric acids, and atomic absorption spectrometric analysis were employed in the assessment. The daily infant intakes of copper decreased from 0.39 mg to 0.16 mg over the ten-month period, zinc from 2.3 mg to 1.2 mg, and selenium from 10.9 mcg to 5.3 mcg. The higher values were obtained through the ingestion of colostrum, while the lower values were the result of consuming mature milk. Comparison of these findings with literature data show the nutrient intake levels of these Burundian infants to be slightly higher than those observed in other poorly nourished countries. The recommended safe and adequate daily intake for infants aged 0-6 months, as proposed by the US National Research Council, is only met for Burundian infants younger than age one month.

Determination of selenium in blood components by X-ray emission spectrometry. Procedures, concentration levels, and health implications.

Sampling, storing, sample pretreatment, and experimental conditions for selenium (Se) determination in human serum, plasma, and whole blood by X-ray emission spectrometric (XRS) methods are described. Concentration levels in these biological fluids, found by this technique, are discussed and compared to values found by other techniques for the same healthy population group in the same area. XRS analysis of blood from patients with various pathological conditions is reviewed, with special attention to the relation of Se with the concentration level of other essential or nonessential trace elements.

Selenium content of livers from sex-linked dwarf and normal broiler breeders. Influence of a thyrotropin-releasing hormone-induced growth hormone release.

Plasma concentrations of cGH, T3, and T4 were not different between dwarf and normal broiler breeders. Normal hens had a liver selenium content of 710 +/- 35 ng/g, and dwarf hens 656 +/- nine ng/g (n = 8). Following injections into a wing vein of different doses (1.5, 3, 6, 12, and 24 micrograms/kg) of the hypothalamic hormone TRH, GH was increased after 15 min. This effect seemed to last longer in dwarf chickens. Plasma concentrations of T3 increased significantly 1 h after TRH in normal hens, but TRH was ineffective in raising T3 levels in dwarf animals. The selenium content of livers obtained following decapitation after 2 h was also increased in normal hens up to 902 +/- 42 ng/g using the highest dose of TRH (24 micrograms/kg). This seemed not to be the case for dwarf animals. A much smaller number of hepatic cGH receptors was also found in dwarf hens, whereas the affinity of the hepatic GH receptor was not influenced by the genotype. It is concluded that the sex-linked dwarf hens are unable to increase their hepatic T4 into T3 conversion following a TRH challenge probably because of a deficiency in hepatic GH receptors. The lower content of selenium in dwarfs and their inability to increase its uptake after TRH seem therefore to support the hypothesis that selenium has a direct role in the activity of the 5'-deiodinase complex.

Estimation of the bioavailability of zinc and calcium from human, cow's, goat, and sheep milk by an in vitro method.

The availability of zinc and calcium from human, cow's, goat, and sheep milk is evaluated by an in vitro method that involves a simulated human gastrointestinal digestion followed by measurement of dialyzability of zinc and calcium. Zinc availability of milk showed the highest value for human milk (15.0%) and the lowest for sheep milk (1.0%), in both whole and skim milk. Calcium availability of the different types of milk did not differ significantly and ranged between 18 and 23%. No significant differences in availability between whole and skim milk were found for both elements, except for zinc in cow's milk.

Diffusibility of selenate, selenite, seleno-methionine, and seleno-cystine during simulated gastrointestinal digestion.

The present study was undertaken to evaluate the in vitro availability of chemically varying forms of selenium (Se), supplemented in cow's milk. Two inorganic (selenite and selenate) and two organic (seleno-methionine [Se-Met] and seleno-cystine [Se-Cys]) Se sources were evaluated. The in vitro availability was estimated by the diffusibility of Se during simulated gastrointestinal digestion. First, the diffusibility was compared after adding a constant amount of Se as either selenate, selenite, seleno-methionine, or Se-Cys in milk samples. Se-Met and selenate were found to be significantly more diffusible than seleno-cystine and selenite under the simulated gastrointestinal conditions. The tendency for superior in vitro availability of selenate and Se-Met compared to selenite and Se-Cys was confirmed for a supplementation range of 5-40 ng/g of Se. This study suggests that the high diffusibility of selenate and Se-Met in a simulated gastrointestinal environment may contribute to their high absorption in vivo.

Indication of silicon essentiality in humans: serum concentrations in Belgian children and adults, including pregnant women.

Serum silicon concentrations were determined in Belgian healthy children and adults, including pregnant women, by electrothermal atomic absorption spectrometry. Serum levels appeared to be significantly higher in healthy children (1-18 yr) than in healthy adults (19-60 yr). Especially, levels in infants (< 1 yr) were higher than in any other group. Compared to age-matched nonpregnants, the serum silicon content was very low in pregnant women. In addition to the fact that this study for the first time provides serum silicon values in adults and children in Belgium, the most important observation is that these serum profiles might be an indication of silicon essentiality in man.