Quality control in the neutron activation analysis of biological markers for selenium in epidemiological investigations

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.

Serum mercury concentration and the risk of ischemic stroke: The REasons for Geographic and Racial Differences in Stroke Trace Element Study

BACKGROUND

Although biologically plausible, epidemiological evidence linking exposure to methylmercury with increased risk of ischemic stroke is limited. The effects of methylmercury may be modified by selenium, which is an anti-oxidant that often co-exists with mercury in fish.

OBJECTIVES

To examine the association between serum mercury levels with the incidence of ischemic stroke and to explore the possible effect modifications by serum selenium levels and demographic and geographic factors.

METHODS

A case-cohort study was designed nested in the REasons for Geographic and Racial Differences in Stroke cohort, including 662 adjudicated incident cases of ischemic stroke and 2494 participants in a randomly selected sub-cohort. Serum mercury was measured using samples collected at recruitment. Multivariable-adjusted hazard ratios (HRs) and the corresponding 95% confidence intervals (CIs) were estimated using the Barlow-weighting method for the Cox proportional hazards regression model.

RESULTS

No statistically significant association was observed between serum mercury concentration and the incidence of ischemic stroke (the highest vs. lowest quintile of mercury levels: HR = 0.82; 95% CI = 0.55-1.22; P for linear trend = 0.42). Sex (P for interaction = 0.06), but not serum selenium levels, modified the association; a more evident trend toward lower incidence of ischemic stroke with higher mercury levels was observed among women.

CONCLUSION

This study does not support an association between mercury and the incidence of ischemic stroke within a population with low-to-moderate level of exposure. Further studies are needed to explore the possibility of mercury-induced ischemic stroke toxicity in other populations at higher exposure levels.

Baseline selenium status and effects of selenium and vitamin e supplementation on prostate cancer risk

BACKGROUND

The Selenium and Vitamin E Cancer Prevention Trial found no effect of selenium supplementation on prostate cancer (PCa) risk but a 17% increased risk from vitamin E supplementation. This case-cohort study investigates effects of selenium and vitamin E supplementation conditional upon baseline selenium status.

METHODS

There were 1739 total and 489 high-grade (Gleason 7-10) PCa cases and 3117 men in the randomly selected cohort. Proportional hazards models estimated hazard ratios (HRs) and 95% confidence intervals (CIs) for effects of supplementation within quintiles of baseline toenail selenium. Cox proportional hazards models were used to estimate hazard ratios, and all statistical tests are two-sided.

RESULTS

Toenail selenium, in the absence of supplementation, was not associated with PCa risk. Selenium supplementation (combined selenium only and selenium + vitamin E arms) had no effect among men with low selenium status (<60th percentile of toenail selenium) but increased the risk of high-grade PCa among men with higher selenium status by 91% (P = .007). Vitamin E supplementation (alone) had no effect among men with high selenium status (≥40th percentile of toenail selenium) but increased the risks of total, low-grade, and high-grade PCa among men with lower selenium status (63%, P = .02; 46%, P = .09; 111%, P = .008, respectively).

CONCLUSIONS

Selenium supplementation did not benefit men with low selenium status but increased the risk of high-grade PCa among men with high selenium status. Vitamin E increased the risk of PCa among men with low selenium status. Men should avoid selenium or vitamin E supplementation at doses that exceed recommended dietary intakes.

Selenium toxicity from a misformulated dietary supplement, adverse health effects, and the temporal response in the nail biologic monitor

Use of dietary supplements in the U.S. has increased steadily over the last 25 years. While misformulation is uncommon, the consequences can be serious. A March 2008 voluntary market recall removed supplement products responsible for the most serious selenium toxicity outbreak that has occurred in the U.S. We quantified selenium concentrations in the misformulated supplement products, measured the temporal response in the nail biologic monitor, and associated exposure to self-reported selenosis symptoms. Subjects recruited through state health departments and referrals provided samples of the misformulated supplement products, exposure information, monthly toenail and or fingernail clippings or onycholysitic nail fragments, and listed their newly onset adverse health effects attributed to selenium toxicity. Ninety-seven subjects enrolled and submitted at least one test sample. Peak selenium concentrations (up to 18.3 and 44.1 μg/g for toenails and fingernails, respectively) were measured. Multiple samples (52 total) of all six recalled supplement lots were analyzed ranging from 22,300 to 32,200 μg selenium per daily dose. Average consumption was 30.9 ± 13.9 doses; 73 subjects provided follow-up data on selenosis symptoms at 2.50 ± 0.14 years. Nail samples accurately reflect exposure in this selenium toxicity outbreak, which resulted in long-term/permanent adverse health effects.

Distribution of toenail selenium levels in young adult Caucasians and African Americans in the United States: the CARDIA Trace Element Study

BACKGROUND

Data on selenium (Se) levels in American young adults, especially in African Americans, are lacking.

OBJECTIVE

This study presented toenail Se distributions in American young adults of both genders, including both Caucasians and African Americans; and explored potential predictors of toenail Se levels.

DATA AND METHODS

Data from the Coronary Artery Risk Development in Young Adults study among 4252 American young adults, aged 20-32 in 1987 was used to examine toenail Se levels by instrumental neutron-activation analysis. The distribution of Se levels was described and multivariable linear regression was used to examine potential modifiers of toenail Se concentration within ethnicity-gender subgroups.

RESULTS

The geometric mean of toenail Se in this cohort was 0.844 μg/g (95% CI, 0.840-0.849 μg/g) and the median was 0.837 μg/g (95% CI, 0.833-0.844 μg/g). Median levels from lowest to highest quintile were 0.691, 0.774, 0.838, 0.913 and 1.037 μg/g. Se levels varied geographically, and were generally in accordance with its concentrations in local soil. Males, African Americans, current smokers, heavy drinkers and less educated participants were more likely to have low Se levels.

CONCLUSION

This study suggests that toenail Se levels vary geographically depending on soil Se concentrations. In addition to gender, ethnicity and education level, smoking status and alcohol consumption are two important indicators of Se status since they are modifiable lifestyle factors. Findings from this study might aid public health professionals in identifying people at relatively high or low Se levels, so that chronic disease prevention efforts can be directed toward these subgroups.

Association of plasma micronutrient levels and urinary isoprostane with risk of lung cancer: the multiethnic cohort study

Although smoking is the primary risk factor for lung cancer, there is evidence to suggest that fruit and vegetable intake are important cofactors. The present case-control study, nested within the Multiethnic Cohort Study, examined the associations of biomarkers of fruit and vegetable intake (individual plasma micronutrient levels), serum selenium, and a urinary biomarker for total lipid peroxidation with lung cancer risk. Two hundred seven incident cases were matched to 414 controls on age, sex, ethnicity, study location (Hawaii or California), smoking status, date/time of collection, and hours of fasting. We measured prediagnositic circulating levels of individual tocopherols and carotenoids, retinol, and serum selenium, and urinary 15-isoprostane F(2t). Conditional logistic regression was used to compute odds ratios (OR) and 95% confidence intervals (CI). For men, strong reductions in risk were seen with increasing tertiles of each plasma carotenoid, with the ORs for the third tertile, compared with the first tertile, ranging from 0.24 to 0.45 (P(trends), 0.002-0.04). No associations were found among women for carotenoids or among either sex for tocopherols, selenium, and retinol. A doubling in risk was seen for men in the second and third tertiles, compared with the first tertile of urinary 15-isoprostane F(2t) (OR, 2.31; 95% CI, 1.02-5.25; and OR, 2.16; 95% CI, 0.98-4.78). This study supports the previously observed association between circulating carotenoids and lung cancer risk in men, and adds to the limited literature regarding urinary 15-isoprostane F(2t) as a marker of cancer risk. Future research examining the possible relationship between isoprostanes and lung cancer is warranted.

Association of selenium, tocopherols, carotenoids, retinol, and 15-isoprostane F(2t) in serum or urine with prostate cancer risk: the multiethnic cohort

OBJECTIVE

We examine the association of antioxidants and 15-isoprostane F(2t) with risk of prostate cancer.

METHODS

We conducted a nested case-control study of serum antioxidant biomarkers (selenium, tocopherols, carotenoids, and retinol) and a urinary oxidation biomarker (15-isoprostane F(2t)) with risk of prostate cancer within the Multiethnic Cohort. Demographic, dietary, and other exposure information was collected by self-administered questionnaire in 1993-1996. We compared prediagnostic biomarker levels from 467 prostate cancer cases and 936 cancer free controls that were matched on several variables. Multivariate conditional logistic regression models were used to compute adjusted odds ratios (ORs) and 95% confidence intervals (CIs).

RESULTS

We observed that there was no overall association of serum concentrations of antioxidants and urinary concentrations of 15-isoprostane F(2t) with risk of prostate cancer or risk of advanced prostate cancer. However, we did observe an inverse association for serum selenium only among African-American men (p trend = 0.02); men in the third tertile of selenium concentrations had a 41% lower risk (95% CI: 0.38-0.93) of prostate cancer when compared to men in the first tertile.

CONCLUSIONS

Overall, our study found no association of serum antioxidants or 15-isoprostane F(2t) with the risk of prostate cancer. The observed inverse association of selenium with prostate cancer in African-Americans needs to be validated in other studies.