A gene-environment interaction analysis of plasma selenium with prevalent and incident diabetes: The Hortega study

Selenium bioactive compounds produced by beneficial microbes

Selenium (Se) is an essential trace element present as selenocysteine (SeCys) in selenoproteins, which have an important role in thyroid metabolism and the redox system in humans. Se deficiency affects between 500 and 1000 million people worldwide. Increasing Se intake can prevent from bacterial and viral infections. Se deficiency has been associated with cancer, Alzheimer, Parkinson, decreased thyroid function, and male infertility. Se intake depends on the food consumed which is directly related to the amount of Se in the soil as well as on its availability. Se is unevenly distributed on the earth's crust, being scarce in some regions and in excess in others. The easiest way to counteract the symptoms of Se deficiency is to enhance the Se status of the human diet. Se salts are the most toxic form of Se, while Se amino acids and Se-nanoparticles (SeNPs) are the least toxic and most bio-available forms. Some bacteria transform Se salts into these Se species. Generally accepted as safe selenized microorganisms can be directly used in the manufacture of selenized fermented and/or probiotic foods. On the other hand, plant growth-promoting bacteria and/or the SeNPs produced by them can be used to promote plant growth and produce crops enriched with Se. In this chapter we discuss bacterial Se metabolism, the effect of Se on human health, the applications of SeNPs and Se-enriched bacteria, as well as their effect on food fortification. Different strategies to counteract Se deficiency by enriching foods using sustainable strategies and their possible implications for improving human health are discussed.

Review on the health-promoting effect of adequate selenium status

Selenium is an essential microelement involved in various biological processes. Selenium deficiency increases the risk of human immunodeficiency virus infection, cancer, cardiovascular disease, and inflammatory bowel disease. Selenium possesses anti-oxidant, anti-cancer, immunomodulatory, hypoglycemic, and intestinal microbiota-regulating properties. The non-linear dose-response relationship between selenium status and health effects is U-shaped; individuals with low baseline selenium levels may benefit from supplementation, whereas those with acceptable or high selenium levels may face possible health hazards. Selenium supplementation is beneficial in various populations and conditions; however, given its small safety window, the safety of selenium supplementation is still a subject of debate. This review summarizes the current understanding of the health-promoting effects of selenium on the human body, the dietary reference intake, and evidence of the association between selenium deficiency and disease.

Role of selenium in type 2 diabetes, insulin resistance and insulin secretion

Selenium is a trace mineral essential for life that acts physiologically through selenoproteins. Among other actions, the endogenous antioxidant selenoprotein glutathione peroxidase and the selenium transporter in blood, selenoprotein P, seem to play an important role in type 2 diabetes mellitus and insulin resistance by weakening the insulin signaling cascade through different mechanisms. Recent findings also suggest that selenoproteins also affect insulin biosynthesis and insulin secretion. This review discussed the role of selenium in type 2 diabetes and the complex interplay between selenoproteins and insulin pathways.

Association of single and joint metals with albuminuria and estimated glomerular filtration longitudinal change in middle-aged adults from Spain: The Aragon workers health study

The nephrotoxicity of low-chronic metal exposures is unclear, especially considering several metals simultaneously. We assessed the individual and joint association of metals with longitudinal change in renal endpoints in Aragon Workers Health Study participants with available measures of essential (cobalt [Co], copper [Cu], molybdenum [Mo] and zinc [Zn]) and non-essential (As, barium [Ba], Cd, chromium [Cr], antimony [Sb], titanium [Ti], uranium [U], vanadium [V] and tungsten [W]) urine metals and albumin-to-creatinine ratio (ACR) (N = 707) and estimated glomerular filtration rate (eGFR) (N = 1493) change. Median levels were 0.24, 7.0, 18.6, 295, 3.1, 1.9, 0.28, 1.16, 9.7, 0.66, 0.22 μg/g for Co, Cu, Mo, Zn, As, Ba, Cd, Cr, Sb, Ti, V and W, respectively, and 52.5 and 27.2 ng/g for Sb and U, respectively. In single metal analysis, higher As, Cr and W concentrations were associated with increasing ACR annual change. Higher Zn, As and Cr concentrations were associated with decreasing eGFR annual change. The shape of the longitudinal dose-responses, however, was compatible with a nephrotoxic role for all metals, both in ACR and eGFR models. In joint metal analysis, both higher mixtures of Cu-Zn-As-Ba-Ti-U-V-W and Co-Cd-Cr-Sb-V-W showed associations with increasing ACR and decreasing eGFR annual change. As and Cr were main drivers of the ACR change joint metal association. For the eGFR change joint metal association, while Zn and Cr were main drivers, other metals also contributed substantially. We identified potential interactions for As, Zn and W by other metals with ACR change, but not with eGFR change. Our findings support that Zn, As, Cr and W and suggestively other metals, are nephrotoxic at relatively low exposure levels. Metal exposure reduction and mitigation interventions may improve prevention and decrease the burden of renal disease in the population.

Biogenic Selenium Nanoparticles in Biomedical Sciences: Properties, Current Trends, Novel Opportunities and Emerging Challenges in Theranostic Nanomedicine

Selenium is an important dietary supplement and an essential trace element incorporated into selenoproteins with growth-modulating properties and cytotoxic mechanisms of action. However, different compounds of selenium usually possess a narrow nutritional or therapeutic window with a low degree of absorption and delicate safety margins, depending on the dose and the chemical form in which they are provided to the organism. Hence, selenium nanoparticles (SeNPs) are emerging as a novel therapeutic and diagnostic platform with decreased toxicity and the capacity to enhance the biological properties of Se-based compounds. Consistent with the exciting possibilities offered by nanotechnology in the diagnosis, treatment, and prevention of diseases, SeNPs are useful tools in current biomedical research with exceptional benefits as potential therapeutics, with enhanced bioavailability, improved targeting, and effectiveness against oxidative stress and inflammation-mediated disorders. In view of the need for developing eco-friendly, inexpensive, simple, and high-throughput biomedical agents that can also ally with theranostic purposes and exhibit negligible side effects, biogenic SeNPs are receiving special attention. The present manuscript aims to be a reference in its kind by providing the readership with a thorough and comprehensive review that emphasizes the current, yet expanding, possibilities offered by biogenic SeNPs in the biomedical field and the promise they hold among selenium-derived products to, eventually, elicit future developments. First, the present review recalls the physiological importance of selenium as an oligo-element and introduces the unique biological, physicochemical, optoelectronic, and catalytic properties of Se nanomaterials. Then, it addresses the significance of nanosizing on pharmacological activity (pharmacokinetics and pharmacodynamics) and cellular interactions of SeNPs. Importantly, it discusses in detail the role of biosynthesized SeNPs as innovative theranostic agents for personalized nanomedicine-based therapies. Finally, this review explores the role of biogenic SeNPs in the ongoing context of the SARS-CoV-2 pandemic and presents key prospects in translational nanomedicine.

Scientific opinion on the tolerable upper intake level for selenium

Following a request from the European Commission, the EFSA Panel on Nutrition, Novel Foods and Food Allergens (NDA) was asked to deliver a scientific opinion on the tolerable upper intake level (UL) for selenium. Systematic reviews of the literature were conducted to identify evidence regarding excess selenium intake and clinical effects and potential biomarkers of effect, risk of chronic diseases and impaired neuropsychological development in humans. Alopecia, as an early observable feature and a well-established adverse effect of excess selenium exposure, is selected as the critical endpoint on which to base a UL for selenium. A lowest-observed-adverse-effect-level (LOAEL) of 330 μg/day is identified from a large randomised controlled trial in humans (the Selenium and Vitamin E Cancer Prevention Trial (SELECT)), to which an uncertainty factor of 1.3 is applied. A UL of 255 μg/day is established for adult men and women (including pregnant and lactating women). ULs for children are derived from the UL for adults using allometric scaling (body weight0.75). Based on available intake data, adult consumers are unlikely to exceed the UL, except for regular users of food supplements containing high daily doses of selenium or regular consumers of Brazil nuts. No risk has been reported with the current levels of selenium intake in European countries from food (excluding food supplements) in toddlers and children, and selenium intake arising from the natural content of foods does not raise reasons for concern. Selenium-containing supplements in toddlers and children should be used with caution, based on individual needs.

[Environment and cardiovascular health: causes, consequences and opportunities in prevention and treatment]

The environment is a strong determinant of cardiovascular health. Environmental cardiology studies the contribution of environmental exposures with the aim of minimizing the harmful influences of pollution and promoting cardiovascular health through specific preventive or therapeutic strategies. The present review focuses on particulate matter and metals, which are the pollutants with the strongest level of scientific evidence, and includes possible interventions. Legislation, mitigation and control of pollutants in air, water and food, as well as environmental policies for heart-healthy spaces, are key measures for cardiovascular health. Individual strategies include the chelation of divalent metals such as lead and cadmium, metals that can only be removed from the body via chelation. The TACT (Trial to Assess Chelation Therapy, NCT00044213) clinical trial demonstrated cardiovascular benefit in patients with a previous myocardial infarction, especially in those with diabetes. Currently, the TACT2 trial (NCT02733185) is replicating the TACT results in people with diabetes. Data from the United States and Argentina have also shown the potential usefulness of chelation in severe peripheral arterial disease. More research and action in environmental cardiology could substantially help to improve the prevention and treatment of cardiovascular disease.

Environment and cardiovascular health: causes, consequences and opportunities in prevention and treatment

The environment is a strong determinant of cardiovascular health. Environmental cardiology studies the contribution of environmental exposures with the aim of minimizing the harmful influences of pollution and promoting cardiovascular health through specific preventive or therapeutic strategies. The present review focuses on particulate matter and metals, which are the pollutants with the strongest level of scientific evidence, and includes possible interventions. Legislation, mitigation and control of pollutants in air, water and food, as well as environmental policies for heart-healthy spaces, are key measures for cardiovascular health. Individual strategies include the chelation of divalent metals such as lead and cadmium, metals that can only be removed from the body via chelation. The TACT (Trial to Assess Chelation Therapy, NCT00044213) clinical trial demonstrated cardiovascular benefit in patients with a previous myocardial infarction, especially in those with diabetes. Currently, the TACT2 trial (NCT02733185) is replicating the TACT results in people with diabetes. Data from the United States and Argentina have also shown the potential usefulness of chelation in severe peripheral arterial disease. More research and action in environmental cardiology could substantially help to improve the prevention and treatment of cardiovascular disease.

Higher selenium was associated with higher risk of diabetes: Consistent evidence from longitudinal and cross-sectional studies based on nail and serum selenium measures

Although the association between selenium (Se) and diabetes has been well-discussed in recent years, few studies have focused on the effects of long-term natural Se exposure and rarely concerned the effects of different Se biomarkers. To address this question, we carried out a 7-year longitudinal study on older adults aged over 65 and another cross-sectional study on middle-aged and older adults aged 40 and above from Chinese soil Se-deplete and Se-optimum areas. Cox proportional hazard models were used to evaluate the associations between nail Se levels and incidence risk of diabetes. Unconditional logistic regression models and analysis of variance models were used to examine the associations between serum Se levels and the prevalence risk of diabetes. The nail and serum Se levels were 0.47 ± 0.20 μg/g and 111.09 ± 55.01 μg/L for the two study populations, respectively. For both of the independent studies, higher Se levels were observed to be associated with a higher risk of diabetes and prediabetes. Compared with the Second nail Se quartile (Q2), the adjusted hazard ratios (HRs) and 95 % confidence intervals (95 % CIs) of diabetes for Q1, Q3 and Q4 were 1.24(0.70, 2.21), 1.53(0.98, 2.39) and 1.31(0.76, 2.26), respectively, and the adjusted HRs (95 % CIs) of prediabetes were 1.47(0.77, 2.81), 1.38(0.83, 2.30), and 1.97(1.13, 3.44), respectively. Compared with the first serum Se quintile (Q1), the adjusted odds ratios (ORs) and 95 % CIs of diabetes for higher quintiles were 1.12(0.75, 1.66), 1.05(0.71, 1.57), 1.09(0.73, 1.62) and 1.51(1.02, 2.19), and the adjusted ORs (95 % CIs) of prediabetes were 1.27(0.77, 2.09), 1.70(1.05, 2.74), 1.94(1.21, 3.11) and 1.67(1.03, 2.71). Our findings consistently suggest that higher Se status is associated with a higher risk of diabetes in adults.

Selenium Status and Its Antioxidant Role in Metabolic Diseases

Selenium (Se), in the form of selenoproteins, is an essential micronutrient that plays an important role in human health and disease. To date, there are at least 25 selenoproteins in humans involved in a wide variety of biological functions, including mammalian development, metabolic progress, inflammation response, chemoprotective properties, and most notably, oxidoreductase functions. In recent years, numerous studies have reported that low Se levels are associated with increased risk, poor outcome, and mortality of metabolic disorders, mainly related to the limited antioxidant defense resulting from Se deficiency. Moreover, the correlation between Se deficiency and Keshan disease has received considerable attention. Therefore, Se supplementation as a therapeutic strategy for preventing the occurrence, delaying the progression, and alleviating the outcomes of some diseases has been widely studied. However, supranutritional levels of serum Se may have adverse effects, including Se poisoning. This review evaluates the correlation between Se status and human health, with particular emphasis on the antioxidant benefits of Se in metabolic disorders, shedding light on clinical treatment.

Gene-environment interaction analysis of redox-related metals and genetic variants with plasma metabolic patterns in a general population from Spain: The Hortega Study

Background

Limited studies have evaluated the joint influence of redox-related metals and genetic variation on metabolic pathways. We analyzed the association of 11 metals with metabolic patterns, and the interacting role of candidate genetic variants, in 1145 participants from the Hortega Study, a population-based sample from Spain.

Methods

Urine antimony (Sb), arsenic, barium (Ba), cadmium (Cd), chromium (Cr), cobalt (Co), molybdenum (Mo) and vanadium (V), and plasma copper (Cu), selenium (Se) and zinc (Zn) were measured by ICP-MS and AAS, respectively. We summarized 54 plasma metabolites, measured with targeted NMR, by estimating metabolic principal components (mPC). Redox-related SNPs (N = 291) were measured by oligo-ligation assay.

Results

In our study, the association with metabolic principal component (mPC) 1 (reflecting non-essential and essential amino acids, including branched chain, and bacterial co-metabolism versus fatty acids and VLDL subclasses) was positive for Se and Zn, but inverse for Cu, arsenobetaine-corrected arsenic (As) and Sb. The association with mPC2 (reflecting essential amino acids, including aromatic, and bacterial co-metabolism) was inverse for Se, Zn and Cd. The association with mPC3 (reflecting LDL subclasses) was positive for Cu, Se and Zn, but inverse for Co. The association for mPC4 (reflecting HDL subclasses) was positive for Sb, but inverse for plasma Zn. These associations were mainly driven by Cu and Sb for mPC1; Se, Zn and Cd for mPC2; Co, Se and Zn for mPC3; and Zn for mPC4. The most SNP-metal interacting genes were NOX1, GSR, GCLC, AGT and REN. Co and Zn showed the highest number of interactions with genetic variants associated to enriched endocrine, cardiovascular and neurological pathways.

Conclusions

Exposures to Co, Cu, Se, Zn, As, Cd and Sb were associated with several metabolic patterns involved in chronic disease. Carriers of redox-related variants may have differential susceptibility to metabolic alterations associated to excessive exposure to metals.

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In a population-based sample, cobalt, copper, selenium, zinc, arsenic, cadmium and antimony exposures were related to some metabolic patterns.

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Carriers of redox-related variants displayed differential susceptibility to metabolic alterations associated to excessive metal exposures.

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Cobalt and zinc showed a number of statistical interactions with variants from genes sharing biological pathways with a role in chronic diseases.

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The metabolic impact of metals combined with variation in redox-related genes might be large in the population, given metals widespread exposure.

A Cross-Sectional Study of Association between Plasma Selenium Levels and the Prevalence of Osteoarthritis: Data from the Xiangya Osteoarthritis Study

OBJECTIVES

Selenium plays an indispensable role in antioxidant and antiinflammation processes. Oxidative stress and inflammation have been hypothesized to be involved in the pathogenesis of cartilage degeneration. We sought to examine the association between plasma selenium levels and the prevalence of radiographic osteoarthritis (ROA).

DESIGN

A population-based cross-sectional study.

SETTING AND PARTICIPANTS

Individuals aged ≥ 50 years were retrieved from the Xiangya Osteoarthritis (XO) Study, a community-based study conducted among the residents of the rural areas of China.

METHODS

Plasma selenium concentration was measured by inductively coupled plasma-dynamic reaction cell-mass spectrometry. ROA was defined as Kellgren/Lawrence score ≥ 2 in at least one knee, hip or hand joint. The association between plasma selenium levels and ROA was evaluated by applying logistic and spline regression.

RESULTS

A total of 1,032 subjects (women: 52.5%; mean age: 63.1 years; ROA prevalence: 45.4%) were included. Compared with the highest tertile, the odds ratios (ORs) for ROA were 1.24 (95% confidence interval [CI]: 0.91 to 1.68) and 1.77 (95% CI: 1.31 to 2.40) in the middle and lowest tertile of plasma selenium, respectively (P for trend<0.05). The results were not changed materially with adjustment of potential confounders. In addition, subjects who had lower plasma selenium levels exhibited a higher prevalence of ROA in a dose-response relationship manner (P=0.005).

CONCLUSION

This study suggests that subjects with lower levels of plasma selenium exhibited a higher prevalence of ROA in a dose-response relationship manner. However, additional studies are still needed to verify the potential causal relationship.

A systematic review and dose-response meta-analysis of exposure to environmental selenium and the risk of type 2 diabetes in nonexperimental studies

Accumulating evidence from both experimental and nonexperimental human studies in the last 15 years indicates that exposure to high levels of the trace element selenium increases the risk of type 2 diabetes. However, the relation of dose to effect is not well understood because randomized controlled trials used only one dose (200 μg/day) of selenium supplementation. While no new trial on this topic has been published since 2018, several nonexperimental studies have appeared. We therefore updated a previous meta-analysis to include recently published observational studies, and incorporated the recently developed one-stage random-effects model to display the dose-response relation between selenium and type 2 diabetes. We retrieved 34 potentially eligible nonexperimental studies on selenium and diabetes risk up to April 15, 2021. The bulk of the evidence indicates a direct relation between blood, dietary and urinary levels of selenium and risk of diabetes, but not with nail selenium, which may be considered a less reliable biomarker. The association was nonlinear, with risk increasing above 80 μg/day of dietary selenium. Whole blood/plasma/serum selenium concentrations of 160 μg/L corresponded to a risk ratio of 1.96 (95% CI 1.27-3.03) compared with a concentration of 90 μg/L (approximately 60 μg of daily selenium intake). The cohort studies, which are less susceptible to reverse causation bias, indicated increased risk for both blood and urine selenium levels and dietary selenium intake, whereas no such pattern emerged from studies relying on nail selenium content. Overall, the nonexperimental studies agree with findings from randomized controlled trials, indicating that moderate to high levels of selenium exposure are associated with increased risk for type 2 diabetes.

Potentialities of selenium nanoparticles in biomedical science

Selenium nanoparticles (SeNPs) have revolutionized biomedical domain and are still developing rapidly. Hence, this perspective elaborates SeNPs properties, synthesis, and biomedical applications, together with their potential for management of SARS-CoV-2.

Association of dietary and serum selenium concentrations with glucose level and risk of diabetes mellitus: A cross sectional study of national health and nutrition examination survey, 1999-2006

BACKGROUND

The associations among dietary selenium intake, serum selenium concentration, plasma glucose and glycosylated hemoglobin levels, and diabetes risk remain controversial. This study aimed to evaluate these associations in adults from the United States.

METHODS

We conducted a cross-sectional study of participants aged 18 years and older who participated in the National Health and Nutrition Examination Survey. Between 1999 and 2006, a total of 41,474 participants were initially included in this study. Multivariable linear or logistic regression analysis was used to investigate the association between dietary selenium intake and serum selenium concentrations, glucose level, and diabetes risk.

RESULTS

The average age of the participants was 30.32 ± 23.95 years, and 48.72 % were men. Their mean dietary selenium intake and mean serum selenium concentration were 98 ± 55 μg per day and 129 ± 22 ng/mL, respectively. Compared with t he lowest quartile of dietary selenium intake, the highest quartile was associated with elevated plasma glucose levels (β = 2.412, 95 % confidence interval [CI]: 0.420, 4.403, P = 0.018), glycosylated hemoglobin levels (β = 0.080, 95 % CI: 0.041, 0.119, P < 0.001), and diabetes risk (odds ratio [OR] = 2.139, 95 % CI: 1.763, 2.596, P < 0.001). Higher serum selenium was also associated with increased plasma glucose levels (β = 12.454, 95 % CI: 4.122, 20.786, P = 0.003) and glycosylated hemoglobin levels (β = 0.326, 95 % CI: 0.187, 0.465, P < 0.001). A generalized additive model with a spline curve suggested a nonlinear relationship between dietary selenium intake, serum selenium and glucose levels, and diabetes risk.

CONCLUSIONS

Dietary selenium intake and serum selenium were positively associated with elevated levels of plasma glucose and glycosylated hemoglobin, and the relationships were nonlinear. Additional selenium supplementation for patients with diabetes may not be recommended.

Co-exposure of serum calcium, selenium and vanadium is nonlinearly associated with increased risk of type 2 diabetes mellitus in a Chinese population

BACKGROUND

Metals play an important role in type 2 diabetes mellitus (T2DM). This study aimed to explore the association of T2DM risk with single metal exposure and multi-metal co-exposure.

METHODS

A case-control study with 223 T2DM patients and 302 controls was conducted. Serum concentrations of 19 metals were determined by inductively coupled plasma mass spectrometry (ICP-MS). Those metals with greater effects were screened out and co-exposure effects of metals were assessed by least absolute shrinkage and selection operator (LASSO) regression.

RESULTS

Serum calcium (Ca), selenium (Se) and vanadium (V) were found with greater effects. Higher levels of Ca and Se were associated with increased T2DM risk (OR = 2.23, 95%CI: 1.38-3.62, P_trend = 0.002; OR = 3.16, 95%CI: 1.82-5.50, P_trend < 0.001), but higher V level was associated with decreased T2DM risk (OR = 0.58, 95%CI: 0.34-0.97, P_trend < 0.001). Serum Ca and V concentrations were nonlinearly associated with T2DM risk (P_overall < 0.001, P_nonliearity < 0.001); however, Se concentration was linearly associated with T2DM risk (P_overall < 0.001, P_nonliearity = 0.389). High co-exposure score of serum Ca, Se and V was associated with increased T2DM risk (OR = 3.50, 95%CI: 2.08-5.89, P_trend < 0.001) as a non-linear relationship (P_overall < 0.001, P_nonliearity = 0.003).

CONCLUSIONS

This study suggest that higher levels of serum Ca and Se were associated with increased T2DM risk, but higher serum V level was associated with decreased T2DM risk. Moreover, co-exposure of serum Ca, Se and V was nonlinearly associated with T2DM risk, and high co-exposure score was positively associated with T2DM risk.

Role of nano-selenium in health and environment

In recent years, researches on selenium nanoparticle have gained more attention due to its important role in many physiological processes. Generally, selenium nanoparticle has a high level of absorption in regular supplementation comparative to selenium. Therefore it is all-important to develop new techniques to elevate the transportation of selenium compounds (selenoproteins, selenoenzymes, etc.) by increasing their bioavailability, bioactivity, and controlled release. SeNPs have special attention regarding their application as food additives and therapeutic agents. Selenium nanoparticle has biomedical and pharmaceutical uses due to its antioxidant, antimicrobial, antidiabetic, and anticancer effects. Selenium nanoparticle is also used to antagonize the toxic effect of chemical and heavy metals. SeNPs are beneficial for the treatment of water and soil contaminated with metals and heavy metals as it has adsorption capability. Selenium nanoparticle is synthesized by the bioreduction of selenium species (sodium selenate, sodium selenite, selenium dioxide, and selenium tetrachloride, etc.) by using bacteria, fungi, plant, and plant extracts, which have given hope for the bioremediation of selenium contaminated water and soils. This article reviews the procedure of selenium nanoparticle synthesis (physical, chemical and biological methods), characterization (UV-vis spectroscopy, transmission electron microscopy, Scanning electron microscopy, electron dispersive X-ray spectroscopy, X-ray diffraction, Fourier transform-infrared spectroscopy, etc.), with the emphasis on its role and application in health and environment.

Selenium deficiency-induced redox imbalance leads to metabolic reprogramming and inflammation in the liver

Selenium (Se) intake disequilibrium is associated with many human diseases (e.g., Keshan disease and type 2 diabetes). To understand the mechanism of Se deficiency-induced hepatic pathogenesis, a pure line pig model was established by feeding a diet with either 0.07 mg/kg Se or 0.3 mg/kg Se for 16 weeks. The hepatic metabolome, lipidome, global proteome, and whole transcriptome were analyzed. Se deficiency causes a redox imbalance via regulation of selenoproteins at both the mRNA and protein level, and blocks the glutathione anti-oxidant system along with enhanced glutathione synthesis and catabolism. The Warburg effect was observed by enhanced activation of the glycolysis and phosphate pentose pathways. The tricarboxylic acid cycle was dysfunctional since the preliminary metabolites decreased and shifted from using glycolysis origin substrates to a glutamine catabolism-preferred metabolic mode. The reprogrammed central carbon metabolism induced widely restrained lipid synthesis. In addition, a Se deficiency initiated inflammation by activating the NF-κB pathway through multiple mechanisms. These results identified the potential metabolic vulnerability of the liver in response to a Se deficiency-induced redox imbalance and possible therapeutic or intervention targets.

Targeted Metabolomics Analysis Reveals that Dietary Supranutritional Selenium Regulates Sugar and Acylcarnitine Metabolism Homeostasis in Pig Liver

BACKGROUND

The association between high selenium (Se) intake and metabolic disorders such as type 2 diabetes has raised great concern, but the underlying mechanism remains unclear.

OBJECTIVE

Through targeted metabolomics analysis, we examined the liver sugar and acylcarnitine metabolism responses to supranutritional selenomethionine (SeMet) supplementation in pigs.

METHODS

Thirty-six castrated male pigs (Duroc-Landrace-Yorkshire, 62.0 ± 3.3 kg) were fed SeMet adequate (Se-A, 0.25 mg Se/kg) or SeMet supranutritional (Se-S, 2.5 mg Se/kg) diets for 60 d. The Se concentration, biochemical, gene expression, enzyme activity, and energy-targeted metabolite profiles were analyzed.

RESULTS

The Se-S group had greater fasting serum concentrations of glucose (1.9-fold), insulin (1.4-fold), and free fatty acids (FFAs,1.3-fold) relative to the Se-A group (P < 0.05). The liver total Se concentration was 4.2-fold that of the Se-A group in the Se-S group (P < 0.05), but expression of most selenoprotein genes and selenoenzyme activity did not differ between the 2 groups. Seven of 27 targeted sugar metabolites and 4 of 21 acylcarnitine metabolites significantly changed in response to high SeMet (P < 0.05). High SeMet supplementation significantly upregulated phosphoenolpyruvate carboxy kinase (PEPCK) activity by 64.4% and decreased hexokinase and succinate dehydrogenase (SDH) activity by 46.5-56.7% (P < 0.05). The relative contents of glucose, dihydroxyacetone phosphate, α-ketoglutarate, fumarate, malate, erythrose-4-phosphate, and sedoheptulose-7-phosphate in the Se-S group were 21.1-360% greater than those in the Se-A group (P < 0.05). The expression of fatty acid synthase (FASN) and the relative contents of carnitine, hexanoyl-carnitine, decanoyl-carnitine, and tetradecanoyl-carnitine in the Se-S group were 35-97% higher than those in the Se-A group (P < 0.05).

CONCLUSIONS

Dietary high SeMet-induced hyperglycemia and hyperinsulinemia were associated with suppression of sugar metabolism and elevation of lipid synthesis in pig livers. Our research provides novel insights into high SeMet intake-induced type 2 diabetes.

Plasma selenium levels and risk of new-onset diabetes in hypertensive adults

OBJECTIVE

The association between plasma selenium and new-onset diabetes in hypertensive adults is still unclear. We aimed to evaluate the relationship of baseline plasma selenium with new-onset diabetes and examine possible effect modifiers in a post-hoc analysis of the China Stroke Primary Prevention Trial (CSPPT).

METHODS

A total of 2367 hypertensive, non-diabetic patients with plasma selenium measurements at baseline were included. The primary outcome was new-onset diabetes, defined as physician-diagnosed diabetes or use of glucose-lowering drugs during the follow-up period, or fasting glucose (FG) ≥126.0 mg/dL at the exit visit.

RESULTS

At baseline, higher FG levels were found among participants with plasma selenium in quartile 4 (≥94.8 μg/L) (β, 1.64 mg/dL; 95%CI: 0.54, 2.73) compared to those in quartiles 1-3. During a median follow-up duration of 4.5 years, new-onset diabetes occurred in 270 (11.4%) participants. Graphic plot showed a positive association between baseline selenium levels and risk of new-onset diabetes. This was further confirmed by adjusted regression analyses; the odds ratios (OR) for new-onset diabetes comparing quartile 4 (≥94.8 μg/L) to quartiles 1-3 was 1.36 (95%CI: 1.01, 1.83). No clear trend was evident across quartiles 1-3.

CONCLUSIONS

Our data suggest that high plasma selenium (≥94.8 μg/L) was associated with increased risk of new-onset diabetes in hypertensive patients.

Systems Biology of Selenium and Complex Disease

Selenium is an essential trace element for maintenance of overall health, whose deficiency and dyshomeostasis have been linked to a variety of diseases and disorders. The majority of previous researches focused on characterization of genes encoding selenoproteins or proteins involved in selenium metabolism as well as their functions. Many studies in humans also investigated the relationship between selenium and complex diseases, but their results have been inconsistent. In recent years, systems biology and "-omics" approaches have been widely used to study complex and global variations of selenium metabolism and function in physiological and different pathological conditions. The present paper reviews recent progress in large-scale and systematic analyses of the relationship between selenium status or selenoproteins and several complex diseases, mainly including population-based cohort studies and meta-analyses, genetic association studies, and some other omics-based studies. Advances in ionomics and its application in studying the interaction between selenium and other trace elements in human health and diseases are also discussed.

Synergistic effect of nano-selenium and metformin on type 2 diabetic rat model: Diabetic complications alleviation through insulin sensitivity, oxidative mediators and inflammatory markers

BACKGROUND AND OBJECTIVES

In the present article, we explore a novel strategy of selenium nanoparticles (Se-NPs) for the treatment of type 2 diabetes mellitus (T2DM) by investigating the effect of Se-NPs alone and in combination with standard anti-diabetic drug metformin (MET) in high-fat diet/streptozotocin (HFD/STZ)-induced T2DM.

METHODS

HFD was supplemented daily to experimental rats for 8 weeks, followed by a single low dose injection of 35 mg/kg of STZ to induce T2DM. The synergistic effect of the different therapeutic strategies on diabetic complications was evaluated after the Se-NPs and MET administration for 8 weeks. Molecular and biochemical analyses were conducted to figure out the effectiveness of our treatment on insulin sensitivity, oxidative mediators and inflammatory markers.

RESULTS

Our observations demonstrated that HFD/STZ-induced rats have a toxic effect on serum and hepatic tissues resulted in inducing remarkable oxidative damage and hyper-inflammation with a significant disturbance in the insulin signaling pathway. Experimental animals either treated with mono-therapeutic-two doses Se-NPs (0.1 and 0.4 mg/kg) and/or MET (100 mg/kg) alone as well as the combined therapy resulted in a remarkable protective anti-diabetic effect illustrated by significant decreases in fasting blood glucose and insulin levels after 8 weeks treatment. At the same time, the levels of active insulin signaling proteins pIRS1/pAKT/pGSK-3β/pAMPK were significantly improved. Moreover, Se-NPs exhibited an anti-inflammatory effect by the mitigation of cytokine expression and a balance between oxidative stress and antioxidant status was restored. Furthermore, the anti-diabetic drug MET administration also exhibited a significant improvement in diabetic complications after the treatment period.

CONCLUSION

This study provides mightily the mechanism of action of combined Se-NPs and MET as a promising therapeutic alternative that synergistically alleviates most of diabetic complications and insulin resistance.

Association between Serum Selenium Level and the Presence of Diabetes Mellitus: A Meta-Analysis of Observational Studies

BACKGROUND

Epidemiological studies have suggested an association between selenium (Se) and diabetes mellitus (DM). However, different studies have reported conflicting results. Therefore, we performed a comprehensive meta-analysis to clarify the impact of Se on DM.

METHODS

We searched the PubMed database for studies on the association between Se and DM from inception to June 2018.

RESULTS

Twenty articles evaluating 47,930 participants were included in the analysis. The meta-analysis found that high levels of Se were significantly associated with the presence of DM (pooled odds ratios [ORs], 1.88; 95% confidence interval [CI], 1.44 to 2.45). However, significant heterogeneity was found (I²=82%). Subgroup analyses were performed based on the Se measurement methods used in each study. A significant association was found between high Se levels and the presence of DM in the studies that used blood (OR, 2.17; 95% CI, 1.60 to 2.93; I²=77%), diet (OR, 1.61; 95% CI, 1.10 to 2.36; I²=0%), and urine (OR, 1.49; 95% CI, 1.02 to 2.17; I²=0%) as samples to estimate Se levels, but not in studies on nails (OR, 1.24; 95% CI, 0.52 to 2.98; I²=91%). Because of significant heterogeneity in the studies with blood, we conducted a sensitivity analysis and tested the publication bias. The results were consistent after adjustment based on the sensitivity analysis as well as the trim and fill analysis for publication bias.

CONCLUSION

This meta-analysis demonstrates that high levels of Se are associated with the presence of DM. Further prospective and randomized controlled trials are warranted to elucidate the link better.

Cohort profile: the Hortega Study for the evaluation of non-traditional risk factors of cardiometabolic and other chronic diseases in a general population from Spain

PURPOSE

The Hortega Study is a prospective study, which investigates novel determinants of selected chronic conditions with an emphasis on cardiovascular health in a representative sample of a general population from Spain.

PARTICIPANTS

In 1997, a mailed survey was sent to a random selection of public health system beneficiaries assigned to the University Hospital Rio Hortega's catchment area in Valladolid (Spain) (n=11 423, phase I), followed by a pilot examination in 1999-2000 of 495 phase I participants (phase II). In 2001-2003, the examination of 1502 individuals constituted the Hortega Study baseline examination visit (phase III, mean age 48.7 years, 49% men, 17% with obesity, 27% current smokers). Follow-up of phase III participants (also termed Hortega Follow-up Study) was obtained as of 30 November 2015 through review of health records (9.5% of participants without follow-up information).

FINDINGS TO DATE

The Hortega Study integrates baseline information of traditional and non-traditional factors (metabolomic including lipidomic and oxidative stress metabolites, genetic variants and environmental factors, such as metals), with 14 years of follow-up for the assessment of mortality and incidence of chronic diseases. Preliminary analysis of time to event data shows that well-known cardiovascular risk factors are associated with cardiovascular incidence rates, which add robustness to our cohort.

FUTURE PLANS

In 2020, we will review updated health and mortality records of this ongoing cohort for a 5-year follow-up extension. We will also re-examine elder survivors to evaluate specific aspects of ageing and conduct geolocation to study additional environmental exposures. Stored biological specimens are available for analysis of new biomarkers. The Hortega Study will, thus, enable the identification of novel factors based on time to event data, potentially contributing to the prevention and control of chronic diseases in ageing populations.

Interactions between plasma copper concentrations and SOD1 gene polymorphism for impaired glucose regulation and type 2 diabetes

Aims

To examine the associations of plasma copper concentrations and superoxide dismutase 1 (SOD1) polymorphisms as well as their gene-environment interaction with newly diagnosed impaired glucose regulation (IGR) and type 2 diabetes (T2D).

Methods

We performed a large case-control study in 2520 Chinese Han subjects: 1004 newly diagnosed T2D patients, 512 newly diagnosed IGR patients and 1004 individuals with normal glucose tolerance.

Results

After multivariable adjustment, the ORs (95% CIs) of T2D across tertiles of plasma copper were 1.00 (reference), 1.85 (95% CI: 1.39, 2.45), and 4.21 (95% CI: 3.20, 5.55) (P-trend < 0.001). Each SD increment of ln-transformed plasma copper was associated with 104% higher odds (OR 2.04, 95%CI 1.82–2.28) increment in ORs of T2D. Meanwhile, compared with the GG genotype of rs2070424, the OR of T2D associated with AG and AA genotypes were 1.44 (95% CI 1.15–1.81) and 1.74 (95% CI 1.33–2.28), respectively. In addition, the positive association between plasma copper and T2D was modified by rs2070424 genotypes. The adjusted ORs and 95% CIs of T2D per SD increment of ln-transformed plasma copper were 2.40 (1.93–2.99), 1.85 (1.59–2.16) and 1.76 (1.44–2.15) in rs2070424 GG, AG and GG carriers respectively (P for interaction < 0.05). Similar interactions were also found for IGR and IGR&T2D. When the joint effects were examined, individuals with rs2070424 AA genotype and the highest tertile of plasma copper concentration had a much higher risk of IGR&T2D (OR 5.34, 95% CI 3.48–8.21) than those with rs2070424 GG genotype and the lowest tertile of plasma copper concentrations.

Conclusions

Plasma copper concentrations are positively and significantly associated with IGR as well as T2D, and these associations may be modified by SOD1 polymorphism. Further studies are warranted to elucidate the potential mechanisms.

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Plasma copper concentrations are positively and significantly associated with IGR as well as T2D.

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Compared with the GG genotype of rs2070424, the risk of T2D associated with AG and AA genotypes were higher.

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The associations between copper and T2D as well as IGR may be modified by SOD1 rs2070424 polymorphism.

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Evaluating the interaction of copper and gene polymorphisms may shed etiologic insight into the copper-diabetes relation.

Association of serum copper, zinc and selenium levels with risk of metabolic syndrome: A nested case-control study of middle-aged and older Chinese adults

Trace elements, such as copper, zinc and selenium, have been linked to the development of metabolic syndrome. However, previous studies concerning these trace elements in association with metabolic syndrome have presented conflicting results in different countries. The aim of this study was to analyse the association between serum copper, zinc and selenium concentrations and the risk of metabolic syndrome among middle-aged and older Chinese adults. We performed a nested case-control study that included 349 individuals who developed metabolic syndrome (125 males and 224 females) during a 3-year follow-up and 349 controls matched by baseline age (±1 years), sex and area. Serum trace element concentrations were measured using atomic absorption spectrometry. The median serum selenium levels in males and females in the metabolic syndrome group were 82.2 (13.4) μg/L and 82.6 (11.1) μg/L, respectively, which were significantly higher than the serum selenium levels in the control group (p = 0.001 and p < 0.001). After adjusting for potential confounders, the odds ratios of risk for metabolic syndrome in the highest tertile of serum selenium levels were 2.72 [95% confidence interval (CI) 1.43-5.20; p for trend 0.002] for males and 5.30 (95% CI 3.31-8.74; p for trend <0.001) for females, respectively, compared with the lowest tertile. In addition, serum selenium levels were positively correlated with postprandial plasma glucose in both genders (for males: odds ratio 2.42; 95% CI 1.27-4.61; for females: odds ratio 2.11; 95% CI 1.32-3.37) and negatively associated with high-density lipoprotein in only females (odds ratio 3.21; 95% CI 1.75-5.91). These results suggest that higher levels of serum selenium might be an independent risk factor for metabolic syndrome, especially in relation to elevated postprandial plasma glucose and reduced high-density lipoprotein levels. However, we failed to demonstrate an association between copper or zinc status and metabolic syndrome or its components.

Selenium and Type 2 Diabetes: Systematic Review

Several studies have investigated the potential role of selenium (Se) in the development of type 2 diabetes (T2D) with disparate findings. We conducted a systematic review and meta-analysis to synthesize the evidence of any association between Se and T2D. PubMed, Embase, and Scopus were searched following the Preferred Reporting Items for Systematic Reviews and Meta-analysis Approach (PRISMA). Sixteen studies from 15 papers met inclusion criteria defined for this review. Of the 13 observational studies included, 8 demonstrated a statistically significant positive association between concentrations of Se and odds for T2D, with odds ratios (95% confidence intervals) ranging from 1.52 (1.01–2.28) to 7.64 (3.34–17.46), and a summary odds ratio (OR) (95% confidence interval (CI)) of 2.03 (1.51–2.72). In contrast, among randomized clinical trials (RCTs) of Se, a higher risk of T2D was not observed for those who received Se compared to a placebo (OR = 1.18, 95% CI 0.95–1.47). Taken together, the results for the relationship between Se and T2D differ between observational studies and randomized clinical trials (RCTs). It remains unclear whether these differences are the result of uncontrolled confounding in the observational studies, or whether there is a modest effect of Se on the risk for T2D that may vary by duration of exposure. Further investigations on the effects of Se on glucose metabolism are needed.

Selenium as a pleiotropic agent for medical discovery and drug delivery

Selenium as a biologically active element lends much support to health maintenance and disease prevention. It is now presenting pleiotropic effects on therapy and drug delivery. In this study, a profiling on the physiological functions, therapeutic significances, clinical/preclinical performances, and biomedical and drug delivery applications of selenium in different modalities was carried out. Major interests focused on selenium-based nanomedicines in confronting various diseases pertaining to selenium or not, especially in antitumor and antidiabetes. Furthermore, the article exclusively discusses selenium nanoparticles featured by ameliorative functions with emphasis on their applications in medical practice and drug delivery. The state-of-the-art in medical discovery as well as research and development on selenium and nano-selenium is discussed in this review.

Selenium supplementation lowers insulin resistance and markers of cardio-metabolic risk in patients with congestive heart failure: a randomised, double-blind, placebo-controlled trial

This study was carried out to evaluate the effects of Se supplementation on metabolic profiles in patients with congestive heart failure (CHF). This randomised double-blind, placebo-controlled trial was performed among fifty-three subjects with CHF, aged 45–85 years old. Subjects were randomly allocated into two groups to take either 200 µg/d of Se as Se yeast (n 26) or placebo (n 27) for 12 weeks. Metabolic profiles were assessed at baseline and at the end of trial. Compared with the placebo, Se supplementation led to significant reductions in serum insulin (−18·41 (sd 27·53) v. +13·73 (sd 23·63) pmol/l, P<0·001), homoeostatic model of assessment for insulin resistance (−1·01 (sd 1·61) v. +0·55 (sd 1·20), P<0·001) and a significant increase in quantitative insulin sensitivity check index (QUICKI) (+0·007 (sd 0·03) v. −0·01 (sd 0·01), P=0·007). In addition, Se supplementation significantly decreased LDL-cholesterol (−0·23 (sd 0·29) v. −0·04 (sd 0·28) mmol/l, P=0·03) and total-:HDL-cholesterol ratio (−0·47 (sd 0·31) v. −0·06 (sd 0·42), P<0·001), and significantly increased HDL-cholesterol levels (+0·18 (sd 0·19) v. +0·02 (sd 0·13) mmol/l, P=0·001) compared with the placebo. In addition, taking Se supplements was associated with a significant reduction in high-sensitivity C-reactive protein (hs-CRP) (−1880·8 (sd 3437·5) v. +415·3 (sd 2116·5) ng/ml, P=0·01), and a significant elevation in plasma total antioxidant capacity (TAC) (+30·9 (sd 118·0) v. −187·9 (sd 412·7) mmol/l, P=0·004) and total glutathione levels (+33·7 (sd 130·4) v. −39·2 (sd 132·8) µmol/l, P=0·003) compared with the placebo. When we applied Bonferroni correction for multiple outcome testing, QUICKI (P=0·11), LDL-cholesterol (P=0·51), hs-CRP (P=0·17), TAC (P=0·06) and GSH (P=0·05) became non-significant, and other metabolic profiles did not alter. Overall, our study supported that Se supplementation for 12 weeks to patients with CHF had beneficial effects on insulin metabolism and few markers of cardio-metabolic risk.

Arsenic exposure, diabetes-related genes and diabetes prevalence in a general population from Spain

Inorganic arsenic exposure may be associated with diabetes, but the evidence at low-moderate levels is not sufficient. Polymorphisms in diabetes-related genes have been involved in diabetes risk. We evaluated the association of inorganic arsenic exposure on diabetes in the Hortega Study, a representative sample of a general population from Valladolid, Spain. Total urine arsenic was measured in 1451 adults. Urine arsenic speciation was available in 295 randomly selected participants. To account for the confounding introduced by non-toxic seafood arsenicals, we designed a multiple imputation model to predict the missing arsenobetaine levels. The prevalence of diabetes was 8.3%. The geometric mean of total arsenic was 66.0 μg/g. The adjusted odds ratios (95% confidence interval) for diabetes comparing the highest with the lowest tertile of total arsenic were 1.76 (1.01, 3.09) and 2.14 (1.47, 3.11) before and after arsenobetaine adjustment, respectively. Polymorphisms in several genes including IL8RA, TXN, NR3C2, COX5A and GCLC showed suggestive differential associations of urine total arsenic with diabetes. The findings support the role of arsenic on diabetes and the importance of controlling for seafood arsenicals in populations with high seafood intake. Suggestive arsenic-gene interactions require confirmation in larger studies.

Selenium for preventing cancer

BACKGROUND

This review is the third update of the Cochrane review "Selenium for preventing cancer". Selenium is a naturally occurring element with both nutritional and toxicological properties. Higher selenium exposure and selenium supplements have been suggested to protect against several types of cancer.

OBJECTIVES

To gather and present evidence needed to address two research questions:1. What is the aetiological relationship between selenium exposure and cancer risk in humans?2. Describe the efficacy of selenium supplementation for cancer prevention in humans.

SEARCH METHODS

We updated electronic searches of the Cochrane Central Register of Controlled Trials (CENTRAL; 2017, Issue 2), MEDLINE (Ovid, 2013 to January 2017, week 4), and Embase (2013 to 2017, week 6), as well as searches of clinical trial registries.

SELECTION CRITERIA

We included randomised controlled trials (RCTs) and longitudinal observational studies that enrolled adult participants.

DATA COLLECTION AND ANALYSIS

We performed random-effects (RE) meta-analyses when two or more RCTs were available for a specific outcome. We conducted RE meta-analyses when five or more observational studies were available for a specific outcome. We assessed risk of bias in RCTs and in observational studies using Cochrane's risk assessment tool and the Newcastle-Ottawa Scale, respectively. We considered in the primary analysis data pooled from RCTs with low risk of bias. We assessed the certainty of evidence by using the GRADE approach.

MAIN RESULTS

We included 83 studies in this updated review: two additional RCTs (10 in total) and a few additional trial reports for previously included studies. RCTs involved 27,232 participants allocated to either selenium supplements or placebo. For analyses of RCTs with low risk of bias, the summary risk ratio (RR) for any cancer incidence was 1.01 (95% confidence interval (CI) 0.93 to 1.10; 3 studies, 19,475 participants; high-certainty evidence). The RR for estimated cancer mortality was 1.02 (95% CI 0.80 to 1.30; 1 study, 17,444 participants). For the most frequently investigated site-specific cancers, investigators provided little evidence of any effect of selenium supplementation. Two RCTs with 19,009 participants indicated that colorectal cancer was unaffected by selenium administration (RR 0.99, 95% CI 0.69 to 1.43), as were non-melanoma skin cancer (RR 1.16, 95% CI 0.30 to 4.42; 2 studies, 2027 participants), lung cancer (RR 1.16, 95% CI 0.89 to 1.50; 2 studies, 19,009 participants), breast cancer (RR 2.04, 95% CI 0.44 to 9.55; 1 study, 802 participants), bladder cancer (RR 1.07, 95% CI 0.76 to 1.52; 2 studies, 19,009 participants), and prostate cancer (RR 1.01, 95% CI 0.90 to 1.14; 4 studies, 18,942 participants). Certainty of the evidence was high for all of these cancer sites, except for breast cancer, which was of moderate certainty owing to imprecision, and non-melanoma skin cancer, which we judged as moderate certainty owing to high heterogeneity. RCTs with low risk of bias suggested increased melanoma risk.Results for most outcomes were similar when we included all RCTs in the meta-analysis, regardless of risk of bias. Selenium supplementation did not reduce overall cancer incidence (RR 0.99, 95% CI 0.86 to 1.14; 5 studies, 21,860 participants) nor mortality (RR 0.81, 95% CI 0.49 to 1.32; 2 studies, 18,698 participants). Summary RRs for site-specific cancers showed limited changes compared with estimates from high-quality studies alone, except for liver cancer, for which results were reversed.In the largest trial, the Selenium and Vitamin E Cancer Trial, selenium supplementation increased risks of alopecia and dermatitis, and for participants with highest background selenium status, supplementation also increased risk of high-grade prostate cancer. RCTs showed a slightly increased risk of type 2 diabetes associated with supplementation. A hypothesis generated by the Nutritional Prevention of Cancer Trial - that individuals with low blood selenium levels could reduce their risk of cancer (particularly prostate cancer) by increasing selenium intake - has not been confirmed. As RCT participants have been overwhelmingly male (88%), we could not assess the potential influence of sex or gender.We included 15 additional observational cohort studies (70 in total; over 2,360,000 participants). We found that lower cancer incidence (summary odds ratio (OR) 0.72, 95% CI 0.55 to 0.93; 7 studies, 76,239 participants) and lower cancer mortality (OR 0.76, 95% CI 0.59 to 0.97; 7 studies, 183,863 participants) were associated with the highest category of selenium exposure compared with the lowest. Cancer incidence was lower in men (OR 0.72, 95% CI 0.46 to 1.14, 4 studies, 29,365 men) than in women (OR 0.90, 95% CI 0.45 to 1.77, 2 studies, 18,244 women). Data show a decrease in risk of site-specific cancers for stomach, colorectal, lung, breast, bladder, and prostate cancers. However, these studies have major weaknesses due to study design, exposure misclassification, and potential unmeasured confounding due to lifestyle or nutritional factors covarying with selenium exposure beyond those taken into account in multi-variable analyses. In addition, no evidence of a dose-response relation between selenium status and cancer risk emerged. Certainty of evidence was very low for each outcome. Some studies suggested that genetic factors might modify the relation between selenium and cancer risk - an issue that merits further investigation.

AUTHORS' CONCLUSIONS

Well-designed and well-conducted RCTs have shown no beneficial effect of selenium supplements in reducing cancer risk (high certainty of evidence). Some RCTs have raised concerns by reporting a higher incidence of high-grade prostate cancer and type 2 diabetes in participants with selenium supplementation. No clear evidence of an influence of baseline participant selenium status on outcomes has emerged in these studies.Observational longitudinal studies have shown an inverse association between selenium exposure and risk of some cancer types, but null and direct relations have also been reported, and no systematic pattern suggesting dose-response relations has emerged. These studies suffer from limitations inherent to the observational design, including exposure misclassification and unmeasured confounding.Overall, there is no evidence to suggest that increasing selenium intake through diet or supplementation prevents cancer in humans. However, more research is needed to assess whether selenium may modify the risk of cancer in individuals with a specific genetic background or nutritional status, and to investigate possible differential effects of various forms of selenium.