Serum selenium and cancer mortality: a nested case-control study within an age- and sex-stratified sample of the Belgian adult population

Serum trace elements during treatment in pancreatic cancer patients and their associations with cancer prognosis

BACKGROUND & AIMS

In this study, we assessed serum trace element concentrations in patients with pancreatic cancer and compared the results to those of healthy controls and patients with chronic pancreatitis. We evaluated the association between trace element concentrations during cancer treatment and the risk of cancer progression and mortality in pancreatic cancer patients.

METHODS

A retrospective cohort study was conducted at a tertiary center in Korea. Serum trace element concentrations of cobalt (Co), copper (Cu), selenium (Se), and zinc (Zn) were measured at diagnosis using an inductively coupled plasma-mass spectrometry in 124 patients with pancreatic cancer, 50 patients with chronic pancreatitis, and 120 healthy controls. Trace elements were measured after a median of 282.5 (95% confidence interval [CI], 224.0-326.5) days from treatment initiation to assess changes in trace element concentrations during treatment.

RESULTS

Serum Co concentrations were significantly higher in patients with chronic pancreatitis and pancreatic cancer compared to healthy controls, while serum Se concentrations were significantly lower. During treatment, serum concentrations of Cu, Se, and Zn significantly decreased in patients with pancreatic cancer. During the follow-up (median 152.5; 95% CI, 142.8-160.0 months), 85.5% of patients experienced progression or relapse, and 84.7% of patients died. Patients with decreased Se and Zn concentrations during treatment had a higher mortality (hazard ratio [HR], 2.10; 95% CI, 1.31-3.38; P = 0.0020 for Se; HR, 1.72; 95% CI, 1.06-2.79; P = 0.0269 for Zn) compared to those with unchanged or increased trace element concentrations during treatment. Patients with a greater reduction in Zn concentrations during treatment had a higher mortality than those with a smaller reduction (HR, 1.59; 95% CI, 1.01-2.52; P = 0.0483). Patients whose Zn status changed from normal to deficient during treatment had an increased mortality (HR, 1.76; 95% CI, 1.16-2.67, P = 0.0084). Patients with multiple (≥2) trace element deficiencies after treatment had poorer outcomes than those with no or single trace element deficiency.

CONCLUSIONS

This study revealed that decreases in Se and Zn concentrations during cancer treatment were associated with adverse outcomes in terms of cancer progression and mortality in patients with pancreatic cancer. Further prospective investigations are recommended.

Correlation between Selenium and Zinc Levels and Survival among Prostate Cancer Patients

The most prevalent type of cancer among males is prostate cancer. Survival is considered quite good, but it can be further improved when risk factors are optimized. One of these factors is micronutrients, including Se and Zn. To our knowledge, the interaction between Se and Zn and prostate cancer remains undescribed. This study aimed to investigate the optimal levels of selenium (Se) and zinc (Zn) and their impact on the survival of individuals diagnosed with prostate cancer. A total of 338 prostate cancer patients were enrolled in this study, which was conducted in Poland between 2009 and 2015. Mass spectrometry, which uses inductively coupled plasma mass, was used to assess serum element levels before treatment. The study participants were categorized into quartiles (QI-QIV) based on the distributions of Se and Zn levels observed among surviving participants. Cox regression was used to assess the association between serum Se and Zn levels and the survival of prostate cancer patients. Our results reveal the effect of combined Se and Zn levels on survival in prostate cancer patients (SeQI-ZnQI vs. SeQIV-ZnQIV; HR = 20.9). These results need further research to establish Se/Zn norms for different populations.

Strong associations of serum selenoprotein P with all-cause mortality and mortality due to cancer, cardiovascular, respiratory and gastrointestinal diseases in older German adults

BACKGROUND

Selenium is an essential trace mineral. The main function of selenoprotein P (SELENOP) is to transport selenium but it has also been ascribed anti-oxidative effects.

METHODS

To assess the association of repeated measurements of serum SELENOP concentration with all-cause and cause-specific mortality serum SELENOP was measured at baseline and 5-year follow-up in 7,186 and 4,164 participants of the ESTHER study, a German population-based cohort aged 50-74 years at baseline.

RESULTS

During 17.3 years of follow-up, 2,126 study participants (30%) died. The relationship of serum SELENOP concentration with all-cause mortality was L-shaped, with mortality being significantly higher at SELENOP concentrations < 4.1 mg/L, which is near the bottom tertile's cut-off (4.2 mg/L). All-cause mortality of participants in the bottom SELENOP tertile was significantly increased compared to subjects in the top tertile (hazard ratio [95% confidence interval]: 1.35 [1.21-1.50]). SELENOP in the bottom tertile was further associated with increased cardiovascular mortality (1.24 [1.04-1.49]), cancer mortality (1.31 [1.09-1.58]), respiratory disease mortality (2.06 [1.28-3.32]) and gastrointestinal disease mortality (2.04 [1.25-3.32]). The excess risk of all-cause mortality for those in the bottom SELENOP tertile was more than twice as strong in men as in women (interaction of SELENOP and sex; p = 0.008).

CONCLUSIONS

In this large cohort study, serum SELENOP concentration was inversely associated with all-cause and cause-specific mortality. Consistent inverse associations with multiple mortality outcomes might be explained by an impaired selenium transport and selenium deficiency in multiple organs. Trials testing the efficacy of selenium supplements in subjects with low baseline SELENOP concentration are needed.

TRIAL REGISTRATION

Retrospectively registered in the German Clinical Trials Register on Feb 14, 2018 (ID: DRKS00014028).

Prediagnostic Blood Selenium Status and Mortality among Patients with Colorectal Cancer in Western European Populations

A higher selenium (Se) status has been shown to be associated with lower risk for colorectal cancer (CRC), but the importance of Se in survival after CRC diagnosis is not well studied. The associations of prediagnostic circulating Se status (as indicated by serum Se and selenoprotein P (SELENOP) measurements) with overall and CRC-specific mortality were estimated using multivariable Cox proportional hazards regression among 995 CRC cases (515 deaths, 396 from CRC) in the European Prospective Investigation into Cancer and Nutrition (EPIC) cohort. Se and SELENOP serum concentrations were measured on average 46 months before CRC diagnosis. Median follow-up time was 113 months. Participants with Se concentrations in the highest quintile (≥100 µg/L) had a multivariable-adjusted hazard ratio (HR) of 0.73 (95% CI: 0.52-1.02; Ptrend = 0.06) for CRC-specific mortality and 0.77 (95% CI: 0.57-1.03; Ptrend = 0.04) for overall mortality, compared with the lowest quintile (≤67.5 µg/L). Similarly, participants with SELENOP concentrations in the highest (≥5.07 mg/L) compared with the lowest quintile (≤3.53 mg/L) had HRs of 0.89 (95% CI: 0.64-1.24; Ptrend = 0.39) for CRC-specific mortality and 0.83 (95% CI: 0.62-1.11; Ptrend = 0.17) for overall mortality. Higher prediagnostic exposure to Se within an optimal concentration (100-150 µg/L) might be associated with improved survival among CRC patients, although our results were not statistically significant and additional studies are needed to confirm this potential association. Our findings may stimulate further research on selenium's role in survival among CRC patients especially among those residing in geographic regions with suboptimal Se availability.

Sex difference in the association between plasma selenium and first stroke: a community-based nested case-control study

BACKGROUND

To date, there is no clearly defined association between plasma selenium levels and first stroke. We aimed to investigate the association between baseline plasma selenium and first stroke risk in a community-based Chinese population.

METHODS

Using a nested case-control study design, a total of 1255 first stroke cases and 1255 matched controls were analyzed. Participant plasma selenium concentrations were measured by inductively coupled plasma mass spectrometry (ICP-MS), and the association of plasma selenium with first stroke risk was estimated by conditional logistic regression models.

RESULTS

Overall, a non-linear negative association between plasma selenium and first total stroke and first ischemic stroke risks was found in males but not in females. Compared with participants with lower selenium levels (tertile 1-2, < 94.1 ng/mL), participants with higher selenium levels (tertile 3, ≥ 94.1 ng/mL) had significantly lower risks of first total stroke (OR 0.63; 95% CI 0.48, 0.83) and first ischemic stroke (OR 0.61; 95% CI 0.45, 0.83) in males but not in females with first total stroke (OR 0.92; 95% CI 0.69, 1.22) and first ischemic stroke (OR 0.89; 95% CI 0.65, 1.22). Furthermore, a stronger association between plasma selenium and first total stroke was found in males with higher vitamin E levels (≥ 13.5 μg/mL vs. < 13.5 μg/mL P-interaction = 0.007). No significant association was observed between plasma selenium and first hemorrhagic stroke risk in either males or females.

CONCLUSION

Our study indicated a significant, non-linear, negative association between plasma selenium and first stroke in males but not in females.

TRIAL REGISTRATION

ChiCTR1800017274 .

Circulating Selenium and Cardiovascular or All-Cause Mortality in the General Population: a Meta-Analysis

The association of circulating selenium level with mortality remains controversial. This meta-analysis investigated the association between elevated circulating selenium level and cardiovascular or all-cause mortality in the general population. PubMed and Embase databases (up to January 20, 2019) were searched for observational studies or post hoc analyses of randomized controlled trials that evaluated the association between elevated circulating selenium level and cardiovascular or all-cause mortality in the general population. Twelve observational studies (ten cohort and two case-control studies) with a total of 25,667 individuals were included. Comparison with the lowest and the highest circulating selenium level showed that the pooled risk ratio (RR) values of all-cause mortality and cardiovascular mortality were 1.36 (95% confidence intervals [CI] 1.18-1.58) and 1.35 (95% CI 1.13-1.62), respectively. When analyzed selenium level as a continuous variable, each standard deviation selenium increase significantly reduced 20% all-cause mortality risk. However, the lowest circulating selenium level was not associated with a high risk of coronary mortality (RR 1.43; 95% CI 0.93-2.19). This meta-analysis indicated that low circulating selenium level was associated with higher risk of cardiovascular or all-cause mortality in the general population. Low circulating selenium level did not confer significant effect on coronary death.

Selenium Status in Elderly People: Longevity and Age-Related Diseases

BACKGROUND

Selenium (Se) is a trace element active in selenoproteins, which can regulate oxidative stress. It is generally perceived as an import factor for maintaining health in the elderly.

METHODS

The goal of this review is to discuss selenium concentration in biological samples, primarily serum or plasma, as a function of age and its relation with longevity. The elemental level in various age-related diseases is reviewed.

CONCLUSION

Highest selenium values were observed in healthy adults, while in an elderly population significantly lower concentrations were reported. Variables responsible for contradictory findings are mentioned. Risk and benefits of Se-supplementation still remain under debate.

Five threads: How U-shaped thinking weaves together dogs, men, selenium, and prostate cancer risk

Prostate cancer is one of the leading causes of cancer-related mortality among men living in developed countries, making the development of safe, practical approaches to prostate cancer risk reduction a high research priority. The relationship between prostate cancer risk and selenium, an essential nutrient required for a number of metabolically important enzymes including glutathione peroxidases, has been investigated, but a satisfactory integration of results has proven elusive. Dogs, like men, naturally develop prostate cancer during aging, providing an appropriate context to study the effects of selenium supplementation on the dysregulation of homeostasis that drives cancer development within the aging prostate. In this paper, we summarize the translational significance of research results gained from dog studies on selenium and prostate cancer risk. Our discovery of a U-shaped dose-response between toenail selenium concentration and prostatic DNA damage in dogs remarkably parallels data on the relationship between selenium status and prostate cancer risk in men. Notably, the dog U-curve provides a plausible explanation for the unanticipated increase in prostate cancer incidence among men with highest baseline selenium who received selenium supplementation in the largest-ever prostate cancer prevention trial (SELECT). Moreover, the dog U-curve guided the discovery of a non-antioxidant, anti-carcinogenic mechanism of organic selenium - the preferential triggering of apoptosis in DNA damaged cells, which we have termed "homeostatic housecleaning". Taken together, the data from dogs and men indicate that increasing selenium status will not necessarily be associated with prostate cancer risk reduction. Landing in the trough of the U - achieving mid-range selenium status - is better than being too low or too high. Personalizing health promotion in a more-is-not-necessarily-better world poses distinctive challenges. Dog studies can be relied upon to contribute important insights into dose-dependent and form-dependent effects - two critical aspects of selenium biology that will have to be disentangled if the burgeoning science of selenium is to be translated into effective strategies for human disease prevention. Beyond contributing to understanding the role of selenium in biology, our work situates the concept of U-shaped thinking at the core of personalized medicine and precision nutrition.

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.

Selenophenes: Introducing a New Element into the Core of Non-Steroidal Estrogen Receptor Ligands

The importance of the heterocyclic core elements with peripheral phenolic and alkyl substituents as a dominant structural motif of ligands for the estrogen receptor (ER) has been well recognized. In this study we expanded the structural diversity of core elements by preparing selenium-containing heterocycles and exploring the activities of these selenophenes on the two ERs, ERα and ERβ. Careful structure-activity relationship (SAR) analysis of their ER binding affinities showed that most selenophenes are ERβ-selective, with the position of the phenol substituents on the selenophene core and the nature of these substituents having a marked effect on their binding affinities. The compound bis(2-fluoro-4-hydroxyphenyl)selenophene (2 f) has the highest relative binding affinity (RBA) of 24.3 for ERβ. In transcription assays, most selenophenes were found to exhibit partial to full agonist activity for both ER subtypes, with compounds bis(2-methyl-4-hydroxyphenyl)selenophene (2 b), bis(4-fluoro-3-hydroxyphenyl)3-bromoselenophene (6 f), and 2,3,5-tris(hydroxyphenyl)thiophenes (8 b and 8 d) profiling as superagonists for ERα; however, several compounds display a range of ERα or ERβ antagonistic activities. A few selenophenes exhibited antiproliferative activity, with compound 8 c showing antiproliferative effects similar to that of 4-hydroxytamoxifen in breast cancer MCF-7 cells while being nontoxic to normal VERO cells. These new ligands could act as models for the development of novel agents leading to improved therapeutics that target the estrogen receptor.

Selenium Exposure and Cancer Risk: an Updated Meta-analysis and Meta-regression

The objective of this study was to investigate the associations between selenium exposure and cancer risk. We identified 69 studies and applied meta-analysis, meta-regression and dose-response analysis to obtain available evidence. The results indicated that high selenium exposure had a protective effect on cancer risk (pooled OR = 0.78; 95%CI: 0.73-0.83). The results of linear and nonlinear dose-response analysis indicated that high serum/plasma selenium and toenail selenium had the efficacy on cancer prevention. However, we did not find a protective efficacy of selenium supplement. High selenium exposure may have different effects on specific types of cancer. It decreased the risk of breast cancer, lung cancer, esophageal cancer, gastric cancer, and prostate cancer, but it was not associated with colorectal cancer, bladder cancer, and skin cancer.

Associations between antioxidants and all-cause mortality among US adults with obstructive lung function

Chronic obstructive pulmonary disease is characterised by oxidative stress, but little is known about the associations between antioxidant status and all-cause mortality in adults with this disease. The objective of the present study was to examine the prospective associations between concentrations of α- and β-carotene, β-cryptoxanthin, lutein/zeaxanthin, lycopene, Se, vitamin C and α-tocopherol and all-cause mortality among US adults with obstructive lung function. Data collected from 1492 adults aged 20-79 years with obstructive lung function in the National Health and Nutrition Examination Survey III (1988-94) were used. Through 2006, 629 deaths were identified during a median follow-up period of 14 years. After adjustment for demographic variables, the concentrations of the following antioxidants modelled as continuous variables were found to be inversely associated with all-cause mortality among adults with obstructive lung function: α-carotene (P= 0·037); β-carotene (P= 0·022); cryptoxanthin (P= 0·022); lutein/zeaxanthin (P= 0·004); total carotenoids (P= 0·001); vitamin C (P< 0·001). In maximally adjusted models, only the concentrations of lycopene (P= 0·013) and vitamin C (P= 0·046) were found to be significantly and inversely associated with all-cause mortality. No effect modification by sex was detected, but the association between lutein/zeaxanthin concentrations and all-cause mortality varied by smoking status (P interaction= 0·048). The concentrations of lycopene and vitamin C were inversely associated with all-cause mortality in this cohort of adults with obstructive lung function.

Selenium for preventing cancer

BACKGROUND

This review is an update of the first Cochrane publication on selenium for preventing cancer (Dennert 2011).Selenium is a metalloid with both nutritional and toxicological properties. Higher selenium exposure and selenium supplements have been suggested to protect against several types of cancers.

OBJECTIVES

Two research questions were addressed in this review: What is the evidence for:1. an aetiological relation between selenium exposure and cancer risk in humans? and2. the efficacy of selenium supplementation for cancer prevention in humans?

SEARCH METHODS

We conducted electronic searches of the Cochrane Central Register of Controlled Trials (CENTRAL, 2013, Issue 1), MEDLINE (Ovid, 1966 to February 2013 week 1), EMBASE (1980 to 2013 week 6), CancerLit (February 2004) and CCMed (February 2011). As MEDLINE now includes the journals indexed in CancerLit, no further searches were conducted in this database after 2004.

SELECTION CRITERIA

We included prospective observational studies (cohort studies including sub-cohort controlled studies and nested case-control studies) and randomised controlled trials (RCTs) with healthy adult participants (18 years of age and older).

DATA COLLECTION AND ANALYSIS

For observational studies, we conducted random effects meta-analyses when five or more studies were retrieved for a specific outcome. For RCTs, we performed random effects meta-analyses when two or more studies were available. The risk of bias in observational studies was assessed using forms adapted from the Newcastle-Ottawa Quality Assessment Scale for cohort and case-control studies; the criteria specified in the Cochrane Handbook for Systematic Reviews of Interventions were used to evaluate the risk of bias in RCTs.

MAIN RESULTS

We included 55 prospective observational studies (including more than 1,100,000 participants) and eight RCTs (with a total of 44,743 participants). For the observational studies, we found lower cancer incidence (summary odds ratio (OR) 0.69, 95% confidence interval (CI) 0.53 to 0.91, N = 8) and cancer mortality (OR 0.60, 95% CI 0.39 to 0.93, N = 6) associated with higher selenium exposure. Gender-specific subgroup analysis provided no clear evidence of different effects in men and women (P value 0.47), although cancer incidence was lower in men (OR 0.66, 95% CI 0.42 to 1.05, N = 6) than in women (OR 0.90, 95% CI 0.45 to 1.77, N = 2). The most pronounced decreases in risk of site-specific cancers were seen for stomach, bladder and prostate cancers. However, these findings have limitations due to study design, quality and heterogeneity that complicate interpretation of the summary statistics. Some studies suggested that genetic factors may modify the relation between selenium and cancer risk-a hypothesis that deserves further investigation.In RCTs, we found no clear evidence that selenium supplementation reduced the risk of any cancer (risk ratio (RR) 0.90, 95% CI 0.70 to 1.17, two studies, N = 4765) or cancer-related mortality (RR 0.81, 95% CI 0.49 to 1.32, two studies, N = 18,698), and this finding was confirmed when the analysis was restricted to studies with low risk of bias. The effect on prostate cancer was imprecise (RR 0.90, 95% CI 0.71 to 1.14, four studies, N = 19,110), and when the analysis was limited to trials with low risk of bias, the interventions showed no effect (RR 1.02, 95% CI 0.90 to 1.14, three studies, N = 18,183). The risk of non-melanoma skin cancer was increased (RR 1.44, 95% CI 0.95 to 1.17, three studies, N = 1900). Results of two trials-the Nutritional Prevention of Cancer Trial (NPCT) and the Selenium and Vitamin E Cancer Trial (SELECT)-also raised concerns about possible increased risk of type 2 diabetes, alopecia and dermatitis due to selenium supplements. An early hypothesis generated by NPCT that individuals with the lowest blood selenium levels at baseline could reduce their risk of cancer, particularly of prostate cancer, by increasing selenium intake has not been confirmed by subsequent trials. As the RCT participants were overwhelmingly male (94%), gender differences could not be systematically assessed.

AUTHORS' CONCLUSIONS

Although an inverse association between selenium exposure and the risk of some types of cancer was found in some observational studies, this cannot be taken as evidence of a causal relation, and these results should be interpreted with caution. These studies have many limitations, including issues with assessment of exposure to selenium and to its various chemical forms, heterogeneity, confounding and other biases. Conflicting results including inverse, null and direct associations have been reported for some cancer types.RCTs assessing the effects of selenium supplementation on cancer risk have yielded inconsistent results, although the most recent studies, characterised by a low risk of bias, found no beneficial effect on cancer risk, more specifically on risk of prostate cancer, as well as little evidence of any influence of baseline selenium status. Rather, some trials suggest harmful effects of selenium exposure. To date, no convincing evidence suggests that selenium supplements can prevent cancer in humans.

Selenium is inversely associated with interleukin-6 in the elderly

BACKGROUND

Selenium is an essential trace element with antioxidant property. Decreased serum selenium concentration with aging had been found in previous report. In this study, we aim to investigate the association between serum selenium and the inflammatory cytokine interleukin-6 in the elderly living in long-term care facilities in Taiwan.

MATERIALS AND METHODS

A total of 336 subjects aged 65 years and older (range of age: 65 - 101 years) were recruited from eight long-term care facilities in 2002-2003. Baseline characteristics, anthropometric indices, and biochemical data were obtained. Selenium deficiency was defined as serum selenium concentration < 80 μg/L. Multiple logistic and linear regression analyses were used to examine the relationships between selenium deficiency and interleukin-6 (divided into quartiles).

RESULTS

The prevalence of selenium deficiency was 35.6% in men and 43.2% in women, respectively. After adjusting for potential confounders using multiple logistic regression analysis, interleukin-6 quartiles were significantly associated with selenium deficiency. Compared to the interleukin-6 quartile I, the adjusted odds ratios of having selenium deficiency for interleukin-6 quartile II, III, IV were 1.00(0.50~2.01), 1.24 (0.62~2.50), and 2.35(1.15~4.83), respectively. The increasing odds ratios for selenium deficiency in higher interleukin-6 quartiles revealed dose-response effects (p < 0.05). Moreover, multiple linear regression analysis showed that serum selenium was significantly inversely associated with interleukin-6 after adjusting for potential confounders.

CONCLUSIONS

Serum selenium was inversely associated with inflammatory cytokine interleukin-6 among elderly living in long-term care facilities in Taiwan. Monitoring serum selenium should be considered in these institutionalized elderly.

Selenium for preventing cancer

BACKGROUND

Selenium is a trace element essential to humans. Higher selenium exposure and selenium supplements have been suggested to protect against several types of cancers.

OBJECTIVES

Two research questions were addressed in this review: What is the evidence for1. an aetiological relationship between selenium exposure and cancer risk in women and men?2. the efficacy of selenium supplementation for cancer prevention in women and men?

SEARCH STRATEGY

We searched electronic databases and bibliographies of reviews and included publications.

SELECTION CRITERIA

We included prospective observational studies to answer research question (a) and randomised controlled trials (RCTs) to answer research question (b).

DATA COLLECTION AND ANALYSIS

We conducted random effects meta-analyses of epidemiological data when five or more studies were retrieved for a specific outcome. We made a narrative summary of data from RCTs.

MAIN RESULTS

We included 49 prospective observational studies and six RCTs. In epidemiologic data, we found a reduced cancer incidence (summary odds ratio (OR) 0.69 (95% confidence interval (CI) 0.53 to 0.91) and mortality (OR 0.55, 95% CI 0.36 to 0.83) with higher selenium exposure. Cancer risk was more pronouncedly reduced in men (incidence: OR 0.66, 95% CI 0.42 to 1.05) than in women (incidence: OR 0.90, 95% CI 0.45 to 1.77). These findings have potential limitations due to study design, quality and heterogeneity of the data, which complicated the interpretation of the summary statistics.The RCTs found no protective efficacy of selenium yeast supplementation against non-melanoma skin cancer or L-selenomethionine supplementation against prostate cancer. Study results for the prevention of liver cancer with selenium supplements were inconsistent and studies had an unclear risk of bias. The results of the Nutritional Prevention of Cancer Trial (NPCT) and SELECT raised concerns about possible harmful effects of selenium supplements.

AUTHORS' CONCLUSIONS

No reliable conclusions can be drawn regarding a causal relationship between low selenium exposure and an increased risk of cancer. Despite evidence for an inverse association between selenium exposure and the risk of some types of cancer, these results should be interpreted with care due to the potential limiting factors of heterogeneity and influences of unknown biases, confounding and effect modification.The effect of selenium supplementation from RCTs yielded inconsistent results. To date, there is no convincing evidence that selenium supplements can prevent cancer in men, women or children.

Defining the Optimal Selenium Dose for Prostate Cancer Risk Reduction: Insights from the U-Shaped Relationship between Selenium Status, DNA Damage, and Apoptosis

Our work in dogs has revealed a U-shaped dose response between selenium status and prostatic DNA damage that remarkably parallels the relationship between dietary selenium and prostate cancer risk in men, suggesting that more selenium is not necessarily better. Herein, we extend this canine work to show that the selenium dose that minimizes prostatic DNA damage also maximizes apoptosis-a cancer-suppressing death switch used by prostatic epithelial cells. These provocative findings suggest a new line of thinking about how selenium can reduce cancer risk. Mid-range selenium status (.67-.92 ppm in toenails) favors a process we call "homeostatic housecleaning"-an upregulated apoptosis that preferentially purges damaged prostatic cells. Also, the U-shaped relationship provides valuable insight into stratifying individuals as selenium-responsive or selenium-refractory, based upon the likelihood of reducing their cancer risk by additional selenium. By studying elderly dogs, the only non-human animal model of spontaneous prostate cancer, we have established a robust experimental approach bridging the gap between laboratory and human studies that can help to define the optimal doses of cancer preventives for large-scale human trials. Moreover, our observations bring much needed clarity to the null results of the Selenium and Vitamin E Cancer Prevention Trial (SELECT) and set a new research priority: testing whether men with low, suboptimal selenium levels less than 0.8 ppm in toenails can achieve cancer risk reduction through daily supplementation.

Low serum selenium is associated with anemia among older adults in the United States

OBJECTIVE

We hypothesized that low serum selenium was associated with anemia in humans.

SUBJECTS

A total of 2092 adults aged 65 and older, in the third National Nutrition Examination Survey, Phase 2 (1991-1994) (NHANES III).

METHODS

Examination of the relationship between serum selenium and hematological indices in NHANES III.

RESULTS

Anemia, defined by World Health Organization criteria, was present in 12.9%. Mean serum selenium among non-anemic and anemic adults was 1.60 and 1.51 micromol l(-1) (P=0.0003). The prevalence of anemia among adults in the lowest to highest quartiles of serum selenium was 18.3, 9.5, 9.7 and 6.9%, respectively (P=0.0005). The proportion of adults in the lowest quartile of selenium among those who were non-anemic or who had anemia due to nutritional causes, chronic inflammation, renal disease or unexplained anemia was 9.9, 27.5, 17.5, 24.0 and 15.4%, respectively. An increase in log(e) selenium was associated with a reduced risk of anemia (odds ratio per one standard deviation increase 0.75, 95% confidence interval 0.58-0.97, P=0.03), adjusting for age, race, education, body mass index and chronic diseases.

CONCLUSION

Low serum selenium is independently associated with anemia among older men and women in the United States.

Low plasma selenium concentrations and mortality among older community-dwelling adults: the InCHIANTI Study

AIMS

We examined the relationship between plasma selenium levels at enrollment and all-cause mortality over a 6-year period among participants in the InCHIANTI study.

METHODS

1042 men and women > or =65 years from the InCHIANTI study, a population- based study of older adults living in the Chianti region of Tuscany, a population-based cohort in Tuscany, Italy. Plasma selenium was measured at enrollment (1998-2000), and vital status was ascertained until May 2006.

RESULTS

During follow-up, 237 participants (22.7%) died. At enrollment, mean (SD) plasma selenium concentrations among participants who survived or died were 0.96 (0.14) and 0.87 (0.18) micromol/L (p<0.0001), respectively. The proportion of participants who died, from lowest to highest quartile of selenium, was 41.3, 27.0, 18.1 and 13.5% (p<0.0001 by Mantel-Haenszel chi-square). After adjusting for age, sex, education, and chronic diseases, adults in the lowest quartile of plasma selenium at enrollment had higher mortality compared with those in the highest quartile (Hazard Ratio (HR) 1.60, 95% Confidence Interval (CI) 1.04-2.47, p=0.034).

CONCLUSION

Low plasma selenium may be an independent predictor of mortality among older adults living in the community.

Efficacy of antioxidant supplementation in reducing primary cancer incidence and mortality: systematic review and meta-analysis

OBJECTIVE

To estimate the association between antioxidant use and primary cancer incidence and mortality and to evaluate these effects across specific antioxidant compounds, target organs, and participant subgroups.

METHODS

Multiple electronic databases (MEDLINE, Cochrane Controlled Clinical Trials Register, EMBASE, Science Citation Index) were searched from their dates of inception until August 2005 to identify eligible randomized clinical trials. Random effects meta-analyses estimated pooled relative risks (RRs) and 95% confidence intervals (CIs) that described the effect of antioxidants vs placebo on cancer incidence and cancer mortality.

RESULTS

Twelve eligible trials, 9 of high methodological quality, were identified (total subject population, 104,196). Antioxidant supplementation did not significantly reduce total cancer incidence (RR, 0.99; 95% CI, 0.94-1.04) or mortality (RR, 1.03; 95% CI, 0.92-1.15) or any site-specific cancer incidence. Beta carotene supplementation was associated with an increase in the incidence of cancer among smokers (RR, 1.10; 95% CI, 1.03-1.10) and with a trend toward increased cancer mortality (RR, 1.16; 95% CI, 0.98-1.37). Selenium supplementation was associated with reduced cancer incidence in men (RR, 0.77; 95% CI, 0.64-0.92) but not in women (RR, 1.00; 95% CI, 0.89-1.13, value for interaction, P< .001) and with reduced cancer mortality (RR, 0.78; 95% CI, 0.65-0.94). Vitamin E supplementation had no apparent effect on overall cancer incidence (RR, 0.99; 95% CI, 0.94-1.04) or cancer mortality (RR, 1.04; 95% CI, 0.97-1.12).

CONCLUSION

Beta carotene supplementation appeared to increase cancer incidence and cancer mortality among smokers, whereas vitamin E supplementation had no effect. Selenium supplementation might have anticarcinogenic effects in men and thus requires further research.

Selenium is inversely associated with bladder cancer risk: a report from the Belgian case-control study on bladder cancer

AIM

Selenium is an essential trace element with suspected anticarcinogenic properties in humans. To date, eight epidemiological studies have examined the association between serum selenium concentration and bladder cancer risk.

METHODS

The authors carried out a population case-control study in 178 cases and 362 controls to assess the relationship between bladder cancer risk and selenium serum concentrations. Unconditional logistic regression was calculated to determine odds ratios (OR) for bladder cancer occurrence with corresponding 95% confidence intervals (95% CI). Effect modification by smoking status, low fruit and vegetable intake, retinol equivalent, vitamin C, vitamin E and total antioxidant status were also assessed.

RESULTS

Serum selenium level was negatively associated with bladder cancer risk. After adjustment for sex, age, smoking and occupational exposure, the OR was 0.48 (95% CI 0.29-0.79) comparing the second with the lowest tertile (serum selenium concentration >82.40 microg/L). The adjusted OR for the highest tertile (serum selenium concentration >96.00 microg/L), was 0.30 (95% CI 0.17-0.52) (P-trend <0.001). An increase of 10 microg/L in serum selenium concentration was associated with a significant decreased bladder cancer risk (OR: 0.76; 95% CI 0.67-0.85).

CONCLUSION

This case-control study suggests an inverse association between serum selenium concentration and bladder cancer risk.

Are men with low selenium levels at increased risk of prostate cancer?

A meta-analysis was undertaken to quantitatively determine if men with low selenium levels were at increased risk of prostate cancer. PubMed, EMBASE and current contents were searched to identify relevant studies. The effect size was calculated by pooling the mean difference for serum, plasma and toenail selenium levels (95% confidence intervals) separately and combined using a random effects model. Meta-regression analysis explored possible sources of heterogeneity. Twenty epidemiologic studies were selected. Mean differences were: -5.55 microg/l (-9.82; -1.27; p=0.01), -0.01 microg/g (-0.03; 0.006; p=0.19), -0.52 microg/l (-4.63; 3.58; p=0.80) for serum, toenail and plasma studies, respectively. Overall, the pooled standardized mean difference between cases and controls was; -0.23 (-0.40; -0.05; p=0.01) indicating a possible inverse association between selenium levels and risk of prostate cancer. Differences in selenium levels between populations, a possible threshold effect and the relationship between selenium and the different stages of prostate cancer require further investigation.

Use of selenium in chemoprevention of bladder cancer

The anticarcinogenic potential of selenium was first identified nearly 40 years ago in geographical studies that reported lower death rates for cancer in regions with high levels of selenium. Cancer of the bladder was one of the body sites found to share this inverse association. Although many subsequent studies have been done on selenium and cancer, only a few have specifically assessed the relation with bladder cancer. However, the high recurrence rate and ability to monitor bladder urothelial-cell carcinoma make selenium a good candidate for chemoprevention. Evidence suggests that selenium is a biologically plausible, safe, and efficacious potential chemoprevention agent for bladder cancer. Large tertiary chemoprevention trials are needed to further investigate the role of selenium in the prevention of bladder cancer. Future studies should assess the best dose and form of selenium, and whether the protective effect of selenium differs between the sexes.

Low Serum Selenium Is Associated with Anemia Among Older Women Living in the Community: the Women's Health and Aging Studies I and II

Anemia is common among older adults, and a substantial proportion of anemia in the older population is of indeterminate cause. Low selenium levels have been associated with anemia in animals, but this relationship has not been well characterized in humans. The objective was to determine whether low serum selenium concentrations are associated with anemia among older women. We conducted a cross-sectional analysis of participants in the Women's Health and Aging Studies, a population-based sample of women living in the community in Baltimore, MD, USA. Of 632 women, aged 70-79 yr, 14.1% of women were anemic (hemoglobin <120 g/L). The prevalence of anemia among women in the lowest to highest quartile of serum selenium was 22.4%, 14.6%, 11.9% and 6.6%, respectively (p < 0.0001). An increase in loge selenium was associated with a reduced risk of anemia (odds ratio per 1 SD increase = 0.63, 95% confidence interval = 0.47-0.84), adjusting for age, education, chronic diseases, iron status, and serum interleukin-6. We conclude that low serum selenium is independently associated with anemia among older women living in the community.

Low serum selenium and total carotenoids predict mortality among older women living in the community: the women's health and aging studies

Selenium and the carotenoids play an important role in antioxidant defenses and in the redox regulation involved in inflammation. We tested the hypothesis that low selenium and carotenoids predict mortality in older women living in the community. Women who were enrolled in the Women's Health and Aging Studies I and II in Baltimore, MD (n = 632; 70-79 y old) had serum selenium and carotenoids measured at baseline and were followed for mortality over 60 mo. Median (minimum, maximum) serum selenium and carotenoids were 1.53 (0.73, 2.51) micromol/L and 1.67 (0.13, 9.10) micromol/L; 14.1% of the women died. The 5 major causes of death were heart disease (32.6%), cancer (18.0%), stroke (9.0%), infection (6.7%), and chronic obstructive pulmonary disease (5.6%). Adjusting for age, education, smoking, BMI, poor appetite, and chronic diseases, higher serum selenium [hazard ratio (HR) 0.71, 95% CI 0.56-0.90/1 SD increase in log(e) selenium; P = 0.005] and higher serum total carotenoids (HR 0.77, 95% CI 0.64-0.84/1 SD increase in log(e) total carotenoids; P = 0.009) were associated with a lower risk of mortality. Women living in the community who have higher serum selenium and carotenoids are at a lower risk of death.

Making sense of sex and supplements: differences in the anticarcinogenic effects of selenium in men and women

The role of the essential trace mineral selenium in human health and disease is currently a subject of intense interest. In particular, the possible cancer preventive effects of dietary selenium supplementation are now being investigated in several large, randomized trials. The association between selenium status, genotoxic damage, and cancer risk remains enigmatic because epidemiologic studies have failed to consistently link low selenium status with increased cancer risk in men and women. In this paper, we considered the evidence that there are sex-based differences in the anticarcinogenic effects of selenium in humans. We focused our review on prospective human studies in which the relationship between selenium status and cancer risk in men and women was directly compared. Results from cohort studies conducted in seven countries (Belgium, China, Finland, Japan, Netherlands, Norway, and United States) were used to assess the strength of association between low selenium status and the incidence of all cancers, sex-specific cancers, and cancers at particular anatomic sites. In general, the available data support the hypothesis that cancer risk in men is more profoundly influenced by selenium status than cancer risk in women. Factors contributing to the apparent difference in the effects of selenium on cancer incidence in men and women may include sex-based differences in the metabolism and/or tissue distribution of selenium, as well as sex- or gender-related factors that influence tumor biology. Studies are needed to further define the dose-response relationship between selenium and cancer risk in men and women. A more complete understanding of the mechanisms by which selenium modulates cancer initiation and progression is needed to optimize dietary selenium supplementation as a practical cancer preventive strategy. Ultimately, achieving the ambitious goal of cancer prevention may require sex- and gender-specific approaches.