Selenium intake and metabolic balance of 10 men from a low selenium area of China

Identification of Factors on Blood Selenium Levels in the US Adults: A Cross-Sectional Study

Selenium (Se) is an essential trace element for humans and its low or high concentration in vivo is associated with the high risk of many diseases. It is important to identify influential factors of Se status. The present study aimed to explore the association between several factors (Se intake, gender, age, race, education, body mass index (BMI), income, smoking and alcohol status) and blood Se concentration using the National Health and Nutrition Examination Survey 2017-2020 data. Demographic characteristics, physical examination, health interviews and diets were compared among quartiles of blood Se concentration using the Rao-Scott χ2 test. Se levels were compared between the different groups of factors studied, measuring the strength of their association. A total of 6205 participants were finally included. The normal reference ranges of blood Se concentration were 142.3 (2.5th percentile) and 240.8 μg/L (97.5th percentile), respectively. The mean values of dietary Se intake, total Se intake and blood Se concentration of the participants were 111.5 μg/day, 122.7 μg/day and 188.7 μg/L, respectively, indicating they were in the normal range. Total Se intake was the most important contributor of blood Se concentration. Gender, race, education status, income, BMI, smoking and alcohol status were associated with blood Se concentration.

Associations Between Serum Selenium and Bone Mineral Density in 8-19-year-old children and adolescents: NHANES 2013-2018

The peak bone mass (PBM) in puberty has been proven to be a critical determinant of osteoporosis and brittle fractures in the elderly. Selenium is an essential trace element that could influence bone metabolism in our bodies. However, no study has investigated the impact of selenium status on bone mineral density (BMD) among children and adolescents. This was a cross-section study from National Health and Nutrition Examination Survey (NHANES) in the USA involving participants aged 8-19 years. We conducted multiple linear regression models to assess the relationship between selenium status and BMD among children and adolescents, and then stratified analyses were performed according to genders and races. Smooth curve fits and two-piecewise linear regression models were conducted to explore their nonlinear relationship. A total of 4570 participants (2338 boys and 2232 girls) were included in the present study, with a mean age of 13.57 ± 3.41 years. In the multivariable adjustment model, serum selenium was positively associated with lumbar spine BMD (β = 0.021 95% CI: 0.008, 0.034, P = 0.001). The dose-response analyses indicated a non-linear inverted U-shaped relationship between serum selenium and lumbar spine BMD. Lower and higher selenium concentrations were related to decreased BMD, and the inflection point of serum selenium was 2.60 umol/L. The inverted U-shaped association was also observed in females (inflection point: 2.49 umol/L), males (inflection point: 2.65 umol/L), Non-Hispanic White (inflection point: 2.50 umol/L), Non-Hispanic Black (inflection point: 2.50 umol/L), and other races (Including multi-racial) (inflection point: 2.81 umol/L). Our study first shows a non-linear inversed U-shaped association between selenium status and BMD among children and adolescents. The proper selenium status will benefit bone health in children and adolescents. More research is still required to verify our findings and their potential mechanisms.

Toxicity of repeated oral intake of organic selenium, inorganic selenium, and selenium nanoparticles: A review

BACKGROUND

To protect from toxicity at supra-essential doses of selenium, it is important to determine dose levels at which adverse effects occur.

METHODS

We identified relevant literature on the repeated dosage of selenium and extracted dose descriptors on reported endpoints, except on genotoxicity/carcinogenicity.

RESULTS

Selenium forms with toxicological data were organic ones: selenomethionine, selenocystine/selenocysteine; and inorganic ones, including selenite (SeO₃^2-), selenate (SeO₄^2-), selenium sulphide (SeS₂), selenide (Se^2-) and selenium nanoparticles. Clinical signs of selenium toxicity in humans include a garlicky-smelling breath, hair loss, and nail changes. One human study showed increased mortality following daily ingestion of 300 µg Se per day for 5 years, equal to a lowest-observed-adverse-effect level (LOAEL) of ∼4.3 µg/kg bw/days. The corresponding no-observed-adverse-effect level (NOAEL) was ∼2.9 µg Se/kg bw/day. One study reported an increased risk of type 2 diabetes after ∼2.9 µg Se/kg bw/day, but other studies with similar doses found no increases in mortality or incidence of type 2 diabetes. NOAELs on affected body weight in animal studies were 0.24-1.2 mg Se/kg bw/day. Other endpoints of selenium toxicity in animals include hepatotoxicity with a NOAEL as low as 2 µg/kg bw/day in rats, as well as gastrointestinal, cardiovascular, and reproductive toxicities with NOAELs of 0.6 (gastrointestinal), 0.08, and 0.4 (cardiovascular) and ≥ 0.04 mg Se/kg bw/day (reproductive), respectively.

CONCLUSIONS

Dose descriptors describing selenium toxicity were as low as 2-3 µg Se/kg bw/day.

Absorption, distribution, metabolism and excretion (ADME) of oral selenium from organic and inorganic sources: A review

BACKGROUND

Selenium is a trace element traditionally ingested either in its organic form via food or in its inorganic form through nutritional supplements, while selenium formulated as nanoparticles is a putative long-acting alternative. To understand the physiology and toxicology of the different selenium formulations, it is important to determine how their selenium content is absorbed, distributed, metabolised and excreted; therefore, we reviewed their biokinetics following oral exposure.

METHODS

We retrieved and reviewed the literature on the absorption, distribution, metabolism, and excretion of oral exposure to different forms of selenium.

RESULTS

Selenium in both the organic form (containing carbon to selenium chemical bonds) and the inorganic form is absorbed into the blood in humans. The mean normal blood level of many studies was 139 μg/L. There are indications that selenium from organic sources is more bioavailable than selenium from inorganic sources. Selenium is distributed throughout the body, including in breast milk. The elimination of selenium mainly involves the faecal and urinary pathways, whereas breath, saliva and hair are minor contributors. Urinary metabolites include trimethylselenium ions, selenosugars and Se-methylselenoneine.

CONCLUSION

Selenium is absorbed to a high extent, and selenium from organic sources is more bioavailable than from inorganic sources. Selenium, as expected as an essential trace element, is distributed throughout the body. Selenium is extensively metabolised, and various excretion metabolites have been identified in both urine and breath, while some selenium is also excreted via faeces.

Acute human toxicity and mortality after selenium ingestion: A review

BACKGROUND

Although selenium is an essential element for humans, acute toxicity has been reported after high oral exposure.

METHODS

The published literature on the acute toxicity of oral selenium was gathered and reviewed.

RESULTS

Reported symptoms and signs include abdominal symptoms, such as vomiting, diarrhea, pain, and nausea, as well as garlic-like odor on the breath. In cases of severe toxicity, cardiac and pulmonary symptoms may develop and ultimately lead to mortality. Mortality has been described after the ingestion of gun bluing solutions, which often contain selenous acid among other potentially toxic substances. Mortality has also been reported after the ingestion of other forms of selenium. Ingested doses associated with mortality are in the range of 1-100 mg Se/kg body weight. Blood levels associated with mortality are above 300 μg Se/L (normal level: 100 μg/L), whereas urinary levels associated with the same endpoint are above170 μg Se/L (normal level: 20-90 μg/L).

CONCLUSION

The acute toxicity associated with oral selenium ingestion and the blood and urinary levels of selenium in different cases of poisonings were reviewed. Mortality is a risk of acute selenium poisoning. Concentrations of selenium in blood and urine samples in non-fatal cases are close to those observed in fatal cases.

Selenium in human health and disease

This review covers current knowledge of selenium in the environment, dietary intakes, metabolism and status, functions in the body, thyroid hormone metabolism, antioxidant defense systems and oxidative metabolism, and the immune system. Selenium toxicity and links between deficiency and Keshan disease and Kashin-Beck disease are described. The relationships between selenium intake/status and various health outcomes, in particular gastrointestinal and prostate cancer, cardiovascular disease, diabetes, and male fertility, are reviewed, and recent developments in genetics of selenoproteins are outlined. The rationale behind current dietary reference intakes of selenium is explained, and examples of differences between countries and/or expert bodies are given. Throughout the review, gaps in knowledge and research requirements are identified. More research is needed to improve our understanding of selenium metabolism and requirements for optimal health. Functions of the majority of the selenoproteins await characterization, the mechanism of absorption has yet to be identified, measures of status need to be developed, and effects of genotype on metabolism require further investigation. The relationships between selenium intake/status and health, or risk of disease, are complex but require elucidation to inform clinical practice, to refine dietary recommendations, and to develop effective public health policies.

Selenium in global food systems

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

Dietary selenium intake by men and women in high and low selenium areas of Punjab

OBJECTIVE

To determine the selenium intake of adults residing in high and low selenium areas of rural Punjab.

DESIGN

All food samples consumed by the subjects were collected and analysed for selenium content. Based on food intake data and selenium content of foods, the selenium intake of the subjects was calculated. Hair, fingernails and urine samples from a sub-sample of subjects were collected and analysed for selenium.

SETTING

Three villages from the selenium-endemic area of Nawan Shahr District and two villages from the non-endemic area of Ludhiana District, Punjab, India, were covered.

SUBJECTS

Forty families from each of the two areas, with one adult male and one adult female in the age range of 20-40 years, were surveyed. Thus a total of 80 men and 80 women constituted the study sample.

RESULTS

In the selenium-endemic area, the average selenium intake of both men and women was more than nine times that in the non-endemic area and exceeded the maximum tolerable limit in more than 60% of men. Mean selenium content of the hair, nails and urine of both men and women was tens of times higher than in the non-endemic area.

CONCLUSIONS

High selenium intake in the endemic area resulted in high selenium content in the hair, nails and urine of men and women. In addition, clinical symptoms of selenium toxicity were also observed in some of the subjects. Selenium intake in the non-endemic area was marginally below the suggested value. Based on the study results, steps need to be taken to educate the public in the endemic area to avoid selenium toxicity.

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

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

Sex, age, geographical location, smoking, and alcohol consumption influence serum selenium concentrations in the USA: third National Health and Nutrition Examination Survey, 1988-1994

Selenium has been reported to reduce the risk for heart diseases and cancer. We examined the association of sex, age, geographical location, serum cotinine concentrations, a measure of smoking intensity, and alcohol consumption with serum selenium concentrations in the third National Health and Nutrition Examination Survey (NHANES III), 1988-1994. Study sample consisted of 14,619 apparently healthy individuals (male: 7,102; female: 7,517) aged 14 to >90 years. Sex, age, geographical location, serum cotinine concentrations, and alcohol consumption significantly influenced serum selenium concentrations (P < 0.05). The mean (+/- standard error) serum selenium concentration in men (124.5 +/- 0.20 ng/mL) was significantly higher than in women (122.0 +/- 0.20 ng/mL) (P < 0.0001). Men in the 31-50 y age group had the highest mean serum selenium concentration. In the same age group, women had the lowest mean serum selenium concentration. In both sexes, participants living in the Midwest and West had significantly higher serum selenium concentrations than those living in South and Northeast geographical locations. Serum cotinine was negatively associated with serum selenium concentrations in both men (beta = -0.0108; P < 0.0001 for trend) and women (beta = -0.0097; P < 0.0001 for trend). Alcohol consumption is positively associated with serum selenium in women (beta = 0.0462; P = 0.0044 for trend) but not in men (beta = 0.0015; P = 0.8496 for trend). Although, sex, age, geographical location, smoking, and alcohol intake influenced serum selenium concentrations, clinically low serum selenium concentrations are not common in the USA.

Serum selenium concentration of a healthy northwest Spanish population

Selenium (Se) is an essential element, cofactor for glutathione peroxidase (GSHPx) activity, whose deficiency may induce modifications in the cellular antioxidative status and induce the appearance of different diseases. Current views suggest that a serum Se concentration inferior to 45 micrograms/L may correlate with an increased risk of coronary hearth diseases, coronary atherosclerosis and cancer. Since the Se concentration in human blood varies between geographical areas, we initiated a study to evaluate the Se status in the general healthy population of Barcelona. Serum Se concentration was investigated in a random sample of 150 subjects (age range 18-70 yr) by graphite furnace atomic spectrometry (FLAAS). L'vov platform, Zeeman background correction, and other specifications of stabilized temperature platform furnace (STPF) concept were followed. The results show that in the general population of Barcelona, Se serum concentration ranges between 60 and 106 micrograms/L (X = 80.7 +/- 10 micrograms/L). These values can be considered within the safe limits, since no subject was found with a concentration lower than the threshold of 45 micrograms/L.

Long-term supplementation with selenate and selenomethionine: urinary excretion by New Zealand women

Thirty-six New Zealand women aged between 18 and 23 years received daily for 32 weeks, 200 micrograms Se as Se-enriched yeast (selenomethionine, SeMet), or brewer's yeast mixed with selenate, or no added Se (placebo) in a double-blind trial. Mean daily Se excretion increased with both supplements; the selenate group excreted more than the SeMet group, 123 v. 66 micrograms/d respectively at week 2, equivalent to 57 v. 27% of the dose. Thereafter Se output increased for the SeMet group reaching a plateau at about 100 micrograms/d at week 16, when plasma Se had also plateaued at 190 ng/ml. The selenate group had reached an earlier plateau of 110 ng Se/ml at week 7. There was a close relationship between 24 h urine and plasma Se for the SeMet group but not for the selenate group. Renal plasma clearances showed two distinctly different responses; the clearance of 0.4 ml/min reached by the SeMet group at week 2 plateaued as plasma Se increased almost 2-fold; whereas for the selenate group the clearance varied between 0.8 and 1.1 ml/min whilst plasma Se remained almost constant at 110 ng/ml. Previous studies, also of 200 micrograms Se/d as Se-rich bread, in New Zealand (NZ) and elsewhere showed similar responses to Se-yeast; the selenite response was intermediate between selenate and Se-yeast (SeMet). The full significance of these studies awaits identification of Se components in plasma, glomerular filtrate and urine; meanwhile renal clearances serve as a pointer to changes in the distribution of Se-containing fractions in the plasma. Trimethylselenonium was detected in basal urines, and was a minor component in urines of supplemented NZ subjects at about 1% of the total Se.

Actual daily dietary intake of selenium in Belgium, using duplicate portion sampling

The dietary selenium (Se) intake in Belgium has been re-evaluated. Duplicate meal collection, wet acid destruction and flow injection hydride generation atomic absorption spectrometry were used as techniques. The daily intake ranged from 28.4 micrograms (Liège, Walloon part of the country) to 61.1 micrograms (Vilvoorde, central part of the country). Compared with intakes recently published for other countries, the actual Belgian value corresponds to intermediate ranges of Se intake.

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.

Serum selenium in adult Czechoslovak (central Bohemia) population

The serum selenium levels in 367 healthy adult (25-64 yr) Central Bohemia residents, 176 men and 191 women, were determined using atomic absorption spectrometry. An extremely wide range of values was found in the whole population sample (< 20-296 micrograms/L) as well as in each sex or age category studied. The mean selenium concentration and 95% confidence interval calculated after logarithmic transformation of the data were 74 micrograms/L (71-77) for the whole population sample, 72 micrograms/L (67-76) for men, and 76 micrograms/L (72-81) for women. About 10% of the residents exhibited serum selenium level below 45 micrograms/L. There was no significant correlation between serum selenium and sex, age, or smoking status of participants. However, the lowest average level was found in the group of heavy smoking women: 66 micrograms/L. The selenium status of the Central Bohemia population seems to be below European average. Groups of residents having a very low nutritional selenium intake may be expected to occur in this population.

Supplementation with wheat selenium induces a dose-dependent response in serum and urine of a Se-replete population

In spite of a rather modest dietary intake of selenium (80 micrograms/10 MJ), Norwegian serum Se levels are among the highest in Europe. As part of an ongoing study of Se bioavailability, effects of different doses of wheat Se were investigated in eighteen healthy, Norwegian women. The participants were given Se-rich bread providing 100, 200 and 300 micrograms Se daily for 6 weeks. About 50% of the Se intake was excreted in the urine by week 6, compared with 67% before the intervention started. Serum Se increased by 20, 37 and 53 micrograms/l respectively, in the three group (P less than 0.001). The blood response and renal clearance results compare well with data obtained from less Se-replete populations, and support the hypothesis that selenomethionine from the diet is incorporated into a non-specific amino acid pool. Our study indicates that the intake of wheat Se is the main determinant of blood Se levels in Norway.

Physiological and nutritional importance of selenium

The essential trace element selenium has recently attracted attention because of its potentialities in the maintenance of human health. Selenium forms part of the active site of the peroxide-destroying enzyme glutathione peroxidase, and it also has other functions, for example in biotransformation, detoxification and the immune response. Functional and clinical consequences of selenium deficiency states have been described, and the selenium requirement, which is influenced by the usual selenium exposure, has been discussed. Wide variations have been found in selenium status in different parts of the world, and populations or groups of patients exposed to marginal deficiency are more numerous than was previously thought. Current research activities in the field of human medicine and nutrition are devoted to the possibilities of using selenium for the prevention or treatment of degenerative or free radical diseases such as neurological disorders, inflammatory diseases or cancer. Pharmacological selenium doses are also recommended as an adjuvant in some treatments.

Effect of various levels of selenium in wheat and meat on blood Se status indices and on Se balance in Dutch men

After a 5-week period of low selenium intake, twenty-four Dutch men received 55, 135 or 215 micrograms Se/d as Se-rich meat or bread for a 9-week period. Four unsupplemented subjects served as controls. Plasma Se increased more rapidly than erythrocyte Se levels; the increases were significantly dependent (P less than 0.001) on Se intake level. Glutathione peroxidase (EC 1.11.1.9; GSH-Px) activity in platelets increased rapidly after supplementation and plateaued after 4-9 weeks. At 10 weeks after supplementation ended, plasma Se levels and platelet GSH-Px were still higher than the baseline values whereas erythrocyte Se levels continued to increase. Except for the higher erythrocyte Se levels after supplementation with high-Se meat, there were no differences in bioavailability of Se between meat and wheat products. Daily urinary and faecal Se excretions as well as Se retention increased with an increased Se intake irrespective of the form of the supplement. Regression of Se excretion v. intake indicated that 33 micrograms Se/d is necessary to compensate for urinary and faecal losses.

Selenium in human nutrition in New Zealand

New Zealand's soil has a low concentration of selenium (Se), and its residents have a lower Se status than do most other peoples. However, New Zealanders do not suffer from the Se-responsive ills that afflict their farm animals and some people in China. New Zealanders, particularly those in the South Island, may have adapted to their low Se environment by thriftiness in urinary excretion of Se. Low glutathione peroxidase activities in their tissues have not resulted in noticeable damage or changes. The enzyme activity can be raised to a plateau by Se supplements, but there is no evidence that supplementation leads to better health. Since patterns of coronary heart disease, hypertension, and cancer in New Zealand resemble those in other Western countries, no direct link between these diseases and Se level is likely.

Selenium balance studies in apparently healthy and housebound elderly people eating self-selected diets

1. Metabolic balance studies (5 d) for Se were conducted in twenty-four apparently healthy elderly people (age 69.6-85.4 years), and twenty housebound subjects (age 69.9-85.1 years) with chronic disease. During the study the subjects lived in their own homes, ate self-selected diets and continued their normal daily activities. 2. Geometric mean daily dietary intakes of the two groups were significantly different (P less than 0.01), being 819 (range 310-1631) nmol for the healthy and 475 (range 233-1136) nmol for the housebound elderly. 3. Daily intake of Se significantly correlated with balance in both groups. Solution of the regression equations gave theoretical daily requirements of 447 nmol for the healthy and 419 nmol for the housebound subjects. The healthy elderly were in positive balance of 148 nmol/d for Se and the housebound were in equilibrium with an overall mean retention of 43 nmol/d. 4. Mean levels of Se in blood fractions for the healthy and housebound subjects were significantly different, being 1.65 and 1.40 mumol/l whole blood, 1.45 and 1.21 mumol/l plasma and 5.72 and 5.30 nmol/g haemoglobin in erythrocytes respectively. There was no difference in the whole-blood glutathione peroxidase (EC 1.11.1.9) activities between the two groups. 5. There were clear differences in Se status between the two groups of elderly people. The cause of the positive balance in the healthy subjects remains unexplained.