Toenail Selenium Research Articles

Trace Element Concentrations of Arsenic and Selenium in Toenails and Risk of Prostate Cancer among Pesticide Applicators.

Prostate cancer is a common cancer among males in the US, but little is known about its risk factors, including trace elements. The primary aim of this study was to examine prostate cancer and its association with arsenic and selenium in toenails. We conducted a small, nested case-control study of men residing in Iowa within the Agricultural Health Study cohort, where we also collected toenail samples to test for arsenic and other trace elements. Toenail samples were sent for neutron activation analysis aimed at long-lived trace elements, including arsenic. Logistic regression was used to estimate odds ratios (ORs) for trace element exposures and prostate cancer. A total of 66 prostate cancer cases and 173 healthy controls returned questionnaires, over 99% of which included toenail samples. An increased risk was seen for the highest levels of arsenic (OR = 3.4 confidence interval (CI) of 1.3-8.6 and OR = 2.2, 95% CI of 0.9-5.6) and the highest level of selenium (2.0, 95% CI of 1.0-4.0). These data also show detectable levels of over 50% for 14 of 22 elements detected in the toenails. The association seen here with arsenic and prostate cancer further supports ecological studies finding an association with community levels of arsenic and prostate cancer incidence and mortality.

Toenail and blood selenium mediated regulation of thyroid dysfunction through immune cells: a mediation Mendelian randomization analysis.

Specific nutrients found in food, such as minerals, antioxidants, and macronutrients, have a significant impact on immune function and human health. However, there is currently limited research exploring the relationship between specific nutrients, immune system function, and thyroid dysfunction commonly observed in autoimmune thyroid diseases, which manifest predominantly as hyperthyroidism or hypothyroidism. Therefore, the objective of this study was to investigate the connections between dietary traits and thyroid dysfunction, as well as the potential mediating role of immune cells, using Mendelian randomization (MR) analysis. The two-step MR analysis used single-nucleotide polymorphisms as instruments, with a threshold of p < 5e-08 for nutrients and thyroid dysfunction, and p < 5e-06 for immune cells. Data from different GWAS databases and UK Biobank were combined to analyze 8 antioxidants and 7 minerals, while the data for 4 macronutrients came from a cohort of 235,000 individuals of European. The outcome data (hypothyroidism, N = 3340; hyperthyroidism, N = 1840; free thyroxin [FT4], N = 49,269; thyroid-stimulating hormone [TSH], N = 54,288) were source from the ThyroidOmics consortium. Immune trait data, including 731 immune phenotypes, were collected from the GWAS catalog. The results revealed that nutrient changes, such as lycopene, toenail and blood selenium, and α-tocopherol, impacted the immune system. Immune cells also affected thyroid function, with cDC cells promoting hypothyroidism and median fluorescence intensity (MFI) phenotypes correlating strongly with FT4 levels. Toenail and blood selenium reduce the relative cell counts (RCC) phenotypes of immune cells (CD62L- plasmacytoid DC %DC and transitional B cells %Lymphocyte), thereby diminishing its promoting effect on hypothyroidis. Furthermore, toenail and blood selenium mainly impacted phenotypes in three types of T cells (CD25 + ⁣ + CD8br, CD3 on CD45RA- CD4+, and CD45RA on Terminally Differentiated CD8br), reinforcing the negative regulation of FT4 levels. The role of immune cells as mediators in the relationship between nutrients and thyroid dysfunction highlights their potential as diagnostic or therapeutic markers. Toenail and blood selenium levels can indirectly impact hypothyroidism by influencing the RCC levels of two types of immune cells, and can indirectly affect FT4 levels by influencing three types of T cells.

Benchtop x-ray fluorescence to quantify elemental content in nails non-destructively

Metals continue to impose health issues among world populations. A non-invasive alternative biomarker for assessment of metals and other elements has been explored in other studies using toenail samples. Some benefits of using toenails as biomarkers over blood samples include cost efficiency, ease of collection, and a longer biological half-life within samples. The objective of this study was to employ desktop XRF for the purpose of measuring metal concentrations in human nail samples, thus conducting a non-destructive assessment. These benefits paired with comparable accuracy in exposure detection could prove toenail samples to be a preferred biomarker for many studies. Current elemental quantification techniques in toenail samples could be improved. The standard practice for measuring metal exposure in toenails, inductively coupled plasma mass spectrometry (ICP-MS), has a counterpart in x-ray fluorescence. While maintaining similar quantification capabilities, x-ray fluorescence could provide decreased cost, preservation of samples, and ease of operation. Portable XRF machines have been tested for measuring toenail samples, but they have drastically increased detection limits in comparison to ICP-MS. New benchtop XRF systems should give comparable detection limits to ICP-MS. This study compares the benchtop XRF measurements of lead (Pb), copper (Cu), iron (Fe), and Selenium (Se) levels to that of ICP-MS measurements of toenail samples and calculates estimated detection limits for 23 other elements. We found strong correlations for the toenail lead (R2 = 0.92), copper (R2 = 0.95), selenium (R2 = 0.60), and iron (R2 = 0.77) comparison between desktop XRF and ICP-MS measurements. Median minimum detection limits over the 23 elements were found to be 0.2 μg/g using a 7.5-min measurement. Benchtop XRF provides a lower detection limit than previously studied portable XRF machines, which gives it the capability of accurately detecting almost any desired element in nail samples. Benchtop XRF provides a non-destructive alternative to ICP-MS in surveillance of nail samples.

Associations of Perinatal Metal and Metalloid Exposures with Early Child Behavioral Development Over Time in the New Hampshire Birth Cohort Study.

Research on the neurodevelopmental effects of metal(loid)s has focused mainly on outcomes assessed at one time point, even though brain development progresses over time. We investigated biomarkers of perinatal exposure to metals and changes in child behavior over time. We followed 268 participants from the prospective New Hampshire Birth Cohort Study between birth and age 5 years. We measured arsenic (As), copper (Cu), manganese (Mn), lead (Pb), selenium (Se), and zinc (Zn) in toenails from 6-week-old infants. The Behavioral Symptoms Index (BSI), externalizing, and internalizing symptoms were assessed using the Behavior Assessment System for Children, 2nd edition (BASC-2) at ages 3 and 5 years. Multivariable linear regression was used to estimate associations of metals with behavior change, calculated as the difference in symptom raw scores between 3 and 5 years, in addition to the associations for symptom scores at 3 and 5 years separately. Sex-specific associations were also explored using stratified models and a sex-metal interaction term. Adjusted associations of metals and change in behavior varied by exposure and outcome. Each 1 μg/g increase in ln toenail Cu was associated with improved behavior between 3 and 5 years [BSI: β = - 3.88 (95%CI: - 7.12, - 0.64); Externalizing problems: β = - 2.20 (95%CI: - 4.07, - 0.33)]. Increasing Zn was associated with increased externalizing behavior over time (β = 3.42 (95%CI: 0.60, 6.25). Sex-stratified analyses suggested more pronounced associations among boys compared to girls. Perinatal exposure to metals may alter behavioral development between ages 3 and 5 years. Findings support the need for more research on associations between metals and neurodevelopment over longer time periods.

Diet-derived antioxidants and nonalcoholic fatty liver disease: a Mendelian randomization study.

Whether supplementation with diet-derived antioxidants is beneficial for nonalcoholic fatty liver disease (NAFLD) is still controversial and we hope to answer this question using population-based genetic data. A total of 8485 NAFLD cases and 658,849 healthy controls from four independent NAFLD genome-wide association studies were enrolled in this study. Genetic variants closely associated with the diet-derived antioxidants were selected to predict their circulating levels. A bi-directional Mendelian randomization (MR) design was employed to assess their causations. Genetic correlation analyses suggested inverse associations between diet-derived antioxidants and NAFLD. MR analyses indicated that the odds ratio (OR) of per standard deviation increase in genetically predicted toenail and blood selenium was 1.179 for NAFLD (95% confidence interval [1.083-1.284]). Also, the genetically elevated selenium level was causally associated with increased levels of C-reactive protein, fibrinogen, alkaline phosphatase and glycated hemoglobin. The OR of 1µg/dL increase in genetically predicted serum lycopene was 1.082 (95%CI [1.051-1.113]). No other causal associations were found for NAFLD. However, we observed protective effects of genetically predicted β-carotene (OR = 0.929[0.911-0.947]) and retinol (OR = 0.483[0.460-0.508]) on type 2 diabetes (T2D), and further they could reduce the serum levels of blood lipids and glucose. Reverse MR analysis suggested genetically predicated NAFLD status would not affect the levels of diet-derived antioxidants. Overall, we observed the positive associations of genetically predicted selenium and lycopene with NAFLD. However, the genetically predicted β-carotene and retinol levels were inversely associated with the risk of T2D.

Effects of Selenium on Chronic Kidney Disease: A Mendelian Randomization Study.

Previous observational studies have shown that there is a controversial association between selenium levels and chronic kidney disease (CKD). Our aim was to assess the causal relationship between selenium levels and CKD using Mendelian randomization (MR) analysis. We used the two-sample Mendelian randomization (MR) method to analyze the causal role of selenium levels on CKD risk. The variants associated with selenium levels were extracted from a large genome-wide association study (GWAS) meta-analysis of circulating selenium levels (n = 5477) and toenail selenium levels (n = 4162) in the European population. Outcome data were from the largest GWAS meta-analysis of European-ancestry participants for kidney function to date. Inverse variance weighted (IVW) method was used as the main analysis and a series of sensitivity analyses were carried out to detect potential violations of MR assumptions. The MR analysis results indicate that the genetically predicted selenium levels were associated with decreased estimated glomerular filtration (eGFR) (effect = -0.0042, 95% confidence interval [CI]: -0.0053-0.0031, p = 2.186 × 10-13) and increased blood urea nitrogen (BUN) (effect = 0.0029, 95% confidence interval [CI]: 0.0006-0.0052, p = 0.0136) with no pleiotropy detected. The MR study indicated that an increased level of selenium is a causative factor for kidney function impairment.

A Bidirectional Mendelian Randomization Study of Selenium Levels and Ischemic Stroke.

Background: Previous observational studies have shown that circulating selenium levels are inversely associated with ischemic stroke (IS). Our aims were to evaluate the causal links between selenium levels and IS, and its subtypes by Mendelian randomization (MR) analysis. Methods: We used the two-sample Mendelian randomization (MR) method to determine whether the circulating selenium levels are causally associated with the risk of stroke. We extracted the genetic variants (SNPs) associated with blood and toenail selenium levels from a large genome-wide association study (GWAS) meta-analysis. Inverse variance-weighted (IVW) method was used as the determinant of the causal effects of exposures on outcomes. Results: A total of 4 SNPs (rs921943, rs6859667, rs6586282, and rs1789953) significantly associated with selenium levels were obtained. The results indicated no causal effects of selenium levels on ischemic stroke by MR analysis (OR = 0.968, 95% CI 0.914–1.026, p = 0.269). Meanwhile, there was no evidence of a causal link between circulating selenium levels and subtypes of IS. Conclusion: The MR study indicated no evidence to support the causal links between genetically predicted selenium levels and IS. Our results also did not support the use of selenium supplementation for IS prevention at the genetic level.

Parental metal exposures as potential risk factors for spina bifida in Bangladesh.

Neural tube defects are a pressing public health concern despite advances in prevention from folic acid-based strategies. Numerous chemicals, in particular arsenic, have been associated with neural tube defects in animal models and could influence risk in humans. We investigated the relationship between parental exposure to arsenic and 17 metals and risk of neural tube defects (myelomeningocele and meningocele) in a case control study in Bangladesh. Exposure assessment included analysis of maternal and paternal toenail samples using inductively coupled plasma mass spectrometry (ICP-MS). A total of 278 participants (155 cases and 123 controls) with data collected from 2016 to 2020 were included in the analysis. In the paternal models, a one-unit increase in the natural logarithm of paternal toenail arsenic was associated with a 74% (odds ratio: 1.74, 95% confidence interval: 1.26-2.42) greater odds of having a child with spina bifida, after adjusting for relevant covariates. Additionally, paternal exposure to aluminum, cobalt, chromium, iron, selenium, and vanadium was associated with increased odds of having a child with spina bifida in the adjusted models. In the maternal models, a one-unit increase in the natural logarithm of maternal toenail selenium and zinc levels was related to a 382% greater (odds ratio: 4.82, 95% confidence interval: 1.32-17.60) and 89% lower (odds ratio: 0.11, 95% confidence interval: 0.03-0.42) odds of having a child with spina bifida in the adjusted models, respectively. Results did not suggest an interaction between parental toenail metals and maternal serum folate. Parental toenail levels of numerous metals were associated with increased risk of spina bifida in Bangladeshi infants. Paternal arsenic exposure was positively associated with neural tube defects in children and is of particular concern given the widespread arsenic poisoning of groundwater resources in Bangladesh and the lack of nutritional interventions aimed to mitigate paternal arsenic exposure. The findings add to the growing body of literature of the impact of metals, especially paternal environmental factors, on child health.

Assessing the Causal Role of Selenium in Amyotrophic Lateral Sclerosis: A Mendelian Randomization Study.

Objectives: The relation between selenium overexposure and increased risk of amyotrophic lateral sclerosis (ALS) has been subject to considerable interest. Epidemiologic studies have reported suggestive associations between selenium and ALS, although the causal inference between selenium and ALS remains to be established. Methods: We conducted a two-sample Mendelian randomization (MR) analysis to analyze the causal role of selenium on ALS risk. Variants associated with selenium levels were obtained from the GWAS meta-analysis of circulating selenium levels (n = 5,477) and toenail selenium levels (n = 4,162) in the European population. Outcome data were from the largest ALS GWAS dataset with 20,806 ALS cases and 59,804 controls in the European population. Inverse variance weighted (IVW) method was used as the main analysis, with an array of sensitivity analyses performed to detect potential violations of MR assumptions. Results: Inverse variance weighted (IVW) analysis indicated no evidence of a causal role for selenium levels in ALS development (odds ratio (OR) = 1.02, 95% confidence interval (CI) = 0.96–1.08). Similar results were observed for the sensitivity analyses (OR = 1.00, 95% CI = 0.95–1.07 for weighted median; OR = 1.07, 95% CI = 0.87–1.32 for MR-Egger), with no pleiotropy detected. Conclusions: Although selenium was found associated with ALS according to earlier epidemiologic studies, current evidence based on the population of European ancestry does not support the causal effect of selenium on ALS risk.

Effects of selenium on coronary artery disease, type 2 diabetes and their risk factors: a Mendelian randomization study.

The impact of selenium on coronary artery disease (CAD) and type 2 diabetes (T2D) remains unclear with inconsistent results from observational studies and randomized controlled trials. We used Mendelian randomization to obtain unconfounded estimates of the effect of selenium on CAD, T2D, lipids and glycemic traits. We applied genetic variants strongly (P < 5 × 10-8) associated with blood and toenail selenium to publicly available summary statistics from large consortia genome-wide association studies of CAD (76,014 cases and 264,785 non-cases), T2D (74,124 cases and 824,006 controls), lipids and glycemic traits. Variant specific Wald estimates were combined using inverse variance weighting, with several sensitivity analyses. Genetically predicted selenium was associated with higher T2D (OR 1.27, 95% CI 1.07-1.50, P = 0.006). There was little evidence of an association with CAD. Genetically predicted selenium was associated with lower low-density lipoprotein (LDL) cholesterol, lower high-density lipoprotein (HDL) cholesterol, higher fasting insulin and higher homeostasis model assessment of insulin resistance. These results were not robust to all sensitivity analyses. No associations with triglycerides, fasting glucose or homeostasis model assessment of β-cell function were evident. Our study suggests selenium may increase the risk of T2D, possibly through insulin resistance rather than pancreatic beta cell function, but may reduce lipids. We found little evidence of an association with CAD, although an inverse association cannot be definitively excluded. The effect of selenium on these outcomes warrants further investigation.

Are Obese Patients with Autism Spectrum Disorder More Likely to Be Selenium Deficient? Research Findings on Pre- and Post-Pubertal Children.

Selenium is involved in many metabolic pathways that are critical for life. Information concerning the metabolic effects of selenium in autism spectrum disorder (ASD) and obesity is still conflicting and incomplete. The pre- and post-pubertal selenium profiles of patients with ASD and obesity have not yet been investigated. The goal of the study was to examine selenium content before and after puberty in euthyroid children diagnosed with ASD, compared to age-matched neurotypical controls, with respect to overweight or obesity as a co-existing pathology. Serum, toenail, and 24h urine selenium levels were determined by inductively coupled plasma mass spectrometry in 287 prepubertal children (mean age 8.09 years), divided into groups: ASD with overweight/obesity (ASD+/Ob+); ASD without overweight/obesity (ASD+/Ob−); non-ASD with overweight/obesity (ASD−/Ob+); and non-ASD without overweight/obesity (ASD−/Ob−). The assessment was repeated in 258 of the children after puberty (mean age 14.26 years).The lowest serum (p < 0.001), urine (p < 0.001) and toenail (p < 0.001) selenium levels before and after puberty were observed in ASD+/Ob+ patients, and the highest in ASD−/Ob−. There were no differences in serum/toenail selenium levels between ASD+/Ob− and ASD−/Ob+ groups. The presence of ASD was associatedwith lower serum (p < 0.001) and toenail (p < 0.001) selenium in BMI-matched groups. In neurotypical patients, post-pubertal serum selenium levels were lower (p < 0.001) than pre-pubertal levels. In the multiple linear regression analyses, selenium levels showed inverse relationships with BMI (p < 0.001) and male gender (p < 0.001), irrespective of the sample type. The serum (p = 0.002) and toenail (p < 0.001) selenium levels were inversely associated with the presence of ASD. ASD, obesity/overweight, and male gender have independent impacts on selenium levels in children. Puberty may affect selenium content in neurotypical children of both genders, but not in ASD patients.

Toenail selenium, plasma selenoprotein P and risk of advanced prostate cancer: A nested case-control study.

Low selenium status may be associated with increased risk of prostate cancer (PC), particularly aggressive PC, and variation in selenoprotein genes may constitute an important modifying factor. We aimed to investigate the association between two selenium status biomarkers [toenail selenium, plasma selenoprotein P (SELENOP)] and risk of advanced, high-grade and advanced-stage PC. We further studied whether variations in selenoprotein genes were associated with PC risk and selenium biomarker concentrations. In the "Diet, Cancer and Health" cohort, 27 178 men aged 50 to 65 years were enrolled from 1993 to 1997. Between baseline and 2012, 1160 cohort participants were diagnosed with advanced PC; among these 462 had high-grade and 281 had advanced-stage disease at diagnosis. Each case was risk set-matched to one control. Toenail selenium and plasma SELENOP concentrations were measured by neutron activation analysis and a SELENOP-ELISA, respectively, and genotyping was performed for 27 selected single nucleotide polymorphisms (SNPs) in 12 selenium pathway genes (including seven selenoproteins) by allele-specific PCR. Toenail selenium and circulating SELENOP concentrations were not associated with advanced, high-grade or advanced-stage PC. After adjustment for multiple testing, none of the genes were associated with PC risk. Neither toenail selenium nor plasma SELENOP was associated with advanced, high-grade or advanced-stage PC.

Higher toenail selenium is associated with increased insulin resistance risk in omnivores, but not in vegetarians

BackgroundThe relationship between selenium (Se) and insulin resistance remains unclear. We aim to explore the association between toenail Se levels and insulin resistance through a cross-sectional study comprising Chinese vegetarians and matched omnivores.MethodsIn this study, we enrolled 220 vegetarians and 220 omnivores matched by age and sex from Shanghai. The inductively coupled plasma mass spectrometry method was used to measure toenail Se levels. Dietary Se intakes were assessed by the 24-h dietary recall method. Blood samples were collected to measure fasting blood glucose level and fasting insulin concentrations. Insulin resistance index (HOMA-IR) and insulin secretion index (HOMA-B) were calculated to evaluate insulin resistance. Multi-linear regression analysis was performed to determine the association between toenail Se levels and insulin resistance, after adjusting for confounders.ResultsThe mean ages of vegetarians (76 vegans, 144 lacto-ovo-vegetarians) and omnivores were 35.96 ± 8.73 years and 35.23 ± 8.93 years, respectively. Of these, 180 (81.8%) were female and 40 (18.2%) were male. No association was found between toenail Se levels and insulin resistance in vegetarians. However, the concentration of Se in toenails was positively correlated with fasting insulin levels (β = 1.030, 95%CI: 0.393 to 1.667) and HOMA-IR (β = 0.245, 95%CI: 0.098 to 0.392) in omnivores, after multivariate adjustment for age, sex, BMI, alcohol consumption, income, and daily dietary intakes (energy, protein, fat, carbohydrate, and fiber). This positive relationship persisted only in omnivores whose dietary Se intake was above 60 μg/d.ConclusionsHigher toenail Se levels were associated with increased insulin resistance risk in Chinese omnivores whose dietary Se intake was above 60 μg/d, but not in vegetarians. These findings create awareness on the association of dietary Se intake above 60 μg/d with the risk of insulin resistance.

Assessing the Role of Selenium in Endometrial Cancer Risk: A Mendelian Randomization Study.

Endometrial cancer is the most commonly diagnosed gynecological cancer in developed countries. Based on evidence from observational studies which suggest selenium inhibits the development of several cancers (including lung and prostate cancer), selenium supplementation has been touted as a potential cancer preventative agent. However, randomized controlled trials have not reported benefit for selenium supplementation in reducing cancer risk. For endometrial cancer, limited observational studies have been conducted assessing whether selenium intake, or blood selenium levels, associated with reduced risk, and no randomized controlled trials have been conducted. We performed a two-sample Mendelian randomization analysis to examine the relationship between selenium levels (using a composite measure of blood and toenail selenium) and endometrial cancer risk, using summary statistics for four genetic variants associated with selenium levels at genome-wide significance levels (P < 5 × 10−8), from a study of 12,906 endometrial cancer cases and 108,979 controls, all of European ancestry. Inverse variance weighted (IVW) analysis indicated no evidence of a causal role for selenium levels in endometrial cancer development (OR per unit increase in selenium levels Z-score = 0.99, 95% CI = 0.87–1.14). Similar results were observed for sensitivity analyses robust to the presence of unknown pleiotropy (OR per unit increase in selenium levels Z-score = 0.98, 95% CI 0.89–1.08 for weighted median; OR per unit increase in selenium levels Z-score = 0.90, 95% CI = 0.53–1.50 for MR-Egger). In conclusion, these results do not support the use of selenium supplementation to prevent endometrial cancer.

Selenium and Sex Steroid Hormones in a U.S. Nationally Representative Sample of Men: A Role for the Link between Selenium and Estradiol in Prostate Carcinogenesis?

Given the recent findings from pooled studies about a potential inverse association between selenium levels and prostate cancer risk, this cross-sectional study aimed to investigate the association between serum selenium and serum concentrations of sex steroid hormones including estradiol in a nationally representative sample of U.S. men to investigate one mechanism by which selenium may influence prostate cancer risk. The study included 1,420 men ages 20 years or older who participated in the Third National Health and Nutrition Examination Survey between 1988 and 1994. We calculated age/race-ethnicity-adjusted and multivariable-adjusted geometric mean serum concentrations of total and estimated free testosterone and estradiol, androstanediol glucuronide, and sex hormone binding globulin, and compared them across quartiles of serum selenium. Adjusting for age, race/ethnicity, smoking status, serum cotinine, household income, physical activity, alcohol consumption, and percent body fat, mean total estradiol [e.g., Q1, 38.00 pg/mL (95% confidence interval (CI), 36.03-40.08) vs. Q4, 35.29 pg/mL (95% CI, 33.53-37.14); P trend = 0.050] and free estradiol [e.g., Q1, 0.96 pg/mL (95% CI, 0.92-1.01) vs. Q4, 0.90 (95% CI, 0.85-0.95); P trend = 0.065] concentrations decreased over quartiles of selenium. Stratification by smoking and alcohol consumption, showed that the latter observation was stronger for never smokers (P interaction = 0.073) and those with limited alcohol intake (P interaction = 0.017). No associations were observed for the other sex steroid hormones studied. Our findings suggests that a possible mechanism by which selenium may be protective for prostate cancer is related to estrogen. Further studies of longitudinal measurements of serum and toenail selenium in relation to serum measurements of sex steroid hormones are needed.

Effects of seafood consumption and toenail mercury and selenium levels on cognitive function among American adults: 25 y of follow up.

The aim of this study was to examine the longitudinal association between seafood and intake of long-chain ω-3 polyunsaturated fatty acids (LCω-3 PUFA) and cognitive function and to explore the possible effect modifications owing to mercury (Hg) and selenium (Se) levels. Participants (N = 3231) from the CARDIA (Coronary Artery Risk Development in Young Adults) study underwent baseline examination and were reexamined in eight follow-up visits. Diet was assessed at baseline and in exam years 7 and 20. Toenail Hg and Se were measured at exam year 2. Cognitive function was measured at exam year 25 using three tests: Rey Auditory Verbal Learning Test (RAVLT), Digit Symbol Substitution Test (DSST), and the Stroop test. The general linear regression model was used to examine cumulative average intakes of LCω-3 PUFA and seafood in relation to the cognitive test scores; and to explore the possible effect modifications caused by Hg and Se. LCω-3 PUFA intake was significantly associated with better performance in the DSST test (quintile 5 versus quintile 1; mean difference = 1.74; 95% confidence interval, 0.19-3.29; Ptrend, 0.048]), but not in the RAVLT and Stroop tests. Similar results were observed for intakes of eicosapentaenoic acid, docosahexaenoic acid, and non-fried seafood. The observed associations were more pronounced in participants with body mass index ≥25 kg/m2, but not significantly modified by toenail Hg or Se. This longitudinal study supported the hypothesis that LCω-3 PUFA or non-fried seafood intake is associated with better cognitive performance in psychomotor speed among US adults, especially those who are overweight or obese.

Toenail selenium, genetic variation in selenoenzymes and risk and outcome in glioma

BackgroundSelenium is an essential trace element obtained through diet that plays a critical role in DNA synthesis and protection from oxidative damage. Selenium intake and polymorphisms in selenoproteins have been linked to the risk of certain cancers though data for glioma are sparse. MethodsIn a case-control study of glioma, we examined the associations of selenium in toenails and genetic variants in the selenoenzyme pathway with the risk of glioma and patient survival. A total of 423 genetic variants in 29 candidate genes in the selenoenzyme pathway were studied in 1547 glioma cases and 1014 healthy controls. Genetic associations were also examined in the UK Biobank cohort comprised of 313,868 persons with 322 incident glioma cases. Toenail selenium was measured in a subcohort of 300 glioma cases and 300 age-matched controls from the case-control study. ResultsNone of the 423 variants studied were consistently associated with glioma risk in the case-control and cohort studies. Moreover, toenail selenium in the case-control study had no significant association with glioma risk (p trend = 0.70) or patient survival among 254 patients with high grade tumors (p trend = 0.70). ConclusionThe present study offers no support for the hypothesis that selenium plays a role in the onset of glioma or patient outcome.

Correlates of toenail selenium and its cross-sectional association with metabolic syndrome.

The present study aimed to identify independent correlates of toenail selenium levels and to examine the association between toenail selenium levels and metabolic syndrome in Korean adults. Cross-sectional analysis was conducted using baseline data from the Trace Element Study of Korean Adults in the Yeungnam area, an ongoing cohort study of Korean adults over the age of 35 years. The baseline survey consisted of questionnaires on demographics, lifestyle characteristics and medical information. Dietary information was obtained through a validated semi-quantitative food frequency questionnaire. Toenail selenium levels were quantified using neutron activation analysis. Biomarkers associated with metabolic syndrome were obtained from biennial medical check-ups. In the multivariable-adjusted analyses, independent lifestyle and dietary correlates of higher selenium levels were alcohol drinking (4.62% higher than nondrinking) and egg intake (0.43% higher per weekly serving), whereas current smoking (5.42% lower than nonsmoking) and vegetable consumption (0.05% lower per weekly serving) were associated with lower toenail selenium levels. In the multivariable adjusted logistic regression, no significant association was observed between toenail selenium levels and metabolic syndrome (odds ratio = 1.33, 95% confidence interval = 0.58-3.05). Multiple lifestyle and dietary factors influenced toenail selenium levels, although no meaningful association was observed between toenail selenium levels and metabolic syndrome in Korean adults. Future prospective large-scale cohort studies are required to determine whether there is a causal relationship between selenium levels and metabolic syndrome in Korean adults.

A case-control study of the risk of cutaneous melanoma associated with three selenium exposure indicators

A direct association between exposure to the metalloid selenium and risk of cutaneous melanoma has been suggested by some observational and experimental cohort studies, whereas other studies have yielded inconsistent results. Since some of the inconsistencies may be due to exposure misclassification arising from the use of exposure indicators that do not adequately reflect body tissue selenium content or the levels of the biologically relevant species of this metalloid, we examined this issue using multiple indicators of exposure. We analyzed the relation of selenium exposure with risk of cutaneous melanoma using two different biomarkers, plasma and toenail selenium concentration, and estimated dietary selenium intake in a population-based case-control series (54 cases, 56 controls) from an Italian community. In unmatched and matched logistic regression models as well as nonparametric generalized additive models, higher plasma selenium levels were strongly associated with excess disease risk. In contrast, toenail and dietary selenium exhibited little relation with melanoma risk. The pattern of correlation among indicators of exposure differed by disease status, with dietary intake associated with plasma selenium levels in patients but not in controls. Our data showed that different selenium exposure indicators can yield different inferences about melanoma risk. Although the series was small, our results are consistent with a positive association between circulating levels of selenium and melanoma risk. Further investigation of the exposure classification performance of various selenium biomarkers and of metabolic patterns of the metalloid and of its speciation are needed to help elucidate the relation between selenium exposure and human health.

Toenail mineral concentration and risk of esophageal squamous cell carcinoma, results from the Golestan Cohort Study.

Studies conducted in China linked selenium deficiency to higher risk of esophageal squamous cell carcinoma (ESCC), but this has not been widely tested outside that selenium‐deficient region. The aim of this study was to investigate the association between selenium and other mineral concentrations in toenails and risk of ESCC in a region with high incidence rates. In this nested case–control study, we identified 222 cases of ESCC from the Golestan Cohort Study, Iran, which has followed up 50,045 participants since enrollment (2004–2008). We randomly selected one control for each case matched by age and sex, using incidence density sampling. We used toenail samples collected at baseline to measure the concentration of selenium, zinc, chromium, mercury, and scandium using instrumental neutron activation analysis. Multivariate adjusted logistic regression models were used to estimate odds ratios (OR) and 95% confidence intervals. Median nail selenium, zinc, chromium, and mercury levels were 1.01, 74.59, 0.77, and 0.018 μg/g in cases and 1.02, 75.71, 0.71, and 0.023 μg/g in controls, respectively. The adjusted odds ratios comparing each fourth quartile of mineral status versus the first quartile were as follows: selenium = 0.78 (95% CI, 0.41–1.49); zinc=0.80 (95% CI, 0.42–1.53); chromium = 0.91 (95% CI, 0.46–1.80); and mercury=0.61 (95% CI, 0.27–1.38), and all trend tests were non–significant. The nail selenium concentration in our controls reflects relatively high selenium status. No evidence of association between selenium or chromium concentrations in toenails and the risk of ESCC was detected in this population.