Selenium and Lung Cancer: A Quantitative Analysis of Heterogeneity in the Current Epidemiological Literature

Rhizosphere enrichment and crop utilization of selenium and metals in typical permian soils of Enshi

Enshi, China, is renowned as "Selenium(Se) Capital" where widely distributed soils derived from Permian parent rocks are notably rich in Se, as well as metals, particularly cadmium(Cd). However, the soil enrichment and crop uptake of Se and metals in these high-Se and high-Cd areas are not well understood. To propose the optimal crop planting plan to ensure the safety of agricultural products, we investigated the soils and corresponding typical crops (rice, tea, and maize). The results showed significant soil enrichment of elements, with average contents (mg/kg) as follows: Cr (185), Zn (126), Cu (58.8), Pb (31.1), As (15.7), Se (6.85), Cd (5.41), and Hg (0.211). All soil Se contents were above 0.4 mg/kg, indicating Se-rich soils. Se primarily existed in an organic-bound form, accounting for an average proportion of 61.3%, while Cd was mainly exchangeable, with an average of 62.5%. Cd exhibited higher activity according to the Relative Index of Activity (RIA). Nemerow single-factor index analysis confirmed significant soil contamination, with Cd showing the highest level, followed by Cr and Cu, while Pb had the lowest level. Tea exhibited a high Se rich ratio (82.0%) without exceeding the Cd standard. In contrast, corn and rice had relatively lower Se-rich ratios (42.0% and 51.5% respectively) and high rates of Cd exceeding the standard, at 49.0% and 61.0% respectively. Canonical analysis revealed that rice was more influenced by soil factors related to Se and Cd compared to maize and tea crops. Therefore, tea cultivation in the Enshi Permian soil area is recommended for safe crop production. This study provides insights into the enrichment, fractionation, and bioavailability of soil Se, Cd, and other metals in the high-Se and high-Cd areas of permian stratas in Enshi, offering a scientific basis for selecting local food crops and producing safe Se-rich agricultural products in the region.

Could Selenium Supplementation Prevent COVID-19? A Comprehensive Review of Available Studies

The purpose of this review is to systematically examine the scientific evidence investigating selenium's relationship with COVID-19, aiming to support, or refute, the growing hypothesis that supplementation could prevent COVID-19 etiopathogenesis. In fact, immediately after the beginning of the COVID-19 pandemic, several speculative reviews suggested that selenium supplementation in the general population could act as a silver bullet to limit or even prevent the disease. Instead, a deep reading of the scientific reports on selenium and COVID-19 that are available to date supports neither the specific role of selenium in COVID-19 severity, nor the role of its supplementation in the prevention disease onset, nor its etiology.

Selenium alleviates heart remodeling through Sirt1/AKT/GSK-3β pathway

Selenium, reported as an important medium for maintaining the body's homeostasis, acts to have multiple bioeffects including anti-inflammatory, anti-oxidant and anti-apoptosis effects. However, its role in heart failure still remains unclear. In this study, we explored the effects of selenium on heart failure and its possible mechanism. The heart failure models were induced by aortic banding and isoproterenol. H&E, TUNEL and PSR staining were performed to detect the degree of cardiomyocyte hypertrophy, apoptosis rates and heart fibrosis, respectively. Real-time quantitative polymerase chain reaction (qRT-PCR) was used to detect different mRNA levels, and western blot was applied to assess the expressions of relative proteins. Immunofluorescence staining was used to evaluate α-SMA density. We first found that treatment of selenium alleviated heart fibrosis and the development of heart failure but not cardiomyocyte cross sectional areas. Besides, selenium improved heart levels of superoxide dismutase2 (SOD2), glutathione peroxidase (Gpx) and glutathione (GSH) and the activity of SOD, accompanied by decreased apoptosis rate. In addition, our in vitro study has shown that selenium reduced mRNA levels of collagen Ⅰ and collagen III, expressions of a-SMA, p-AKT/AKT and p-GSK-3β/ GSK-3β, apoptosis rates and reactive oxygen species (ROS) levels in H9C2 cardio-myoblasts treated with TGF-β1. Moreover, the level of Sirt1 was found to be up-regulated by selenium which effects were weakened after the administration of small interfering RNA (siRNA)-Sirt1 or EX527 (inhibitor of Sirt1). Our current results have demonstrated that the protective effects of selenium on heart hypertrophy is through the regulation of Sirt1 and AKT/GSK-3β pathway.

The relationship between dietary selenium intake and telomere length among diabetes

Se is an indispensable trace element for the human body, and telomere length is considered a marker of biological ageing. Previous studies have shown that dietary Se intake is associated with telomere length. However, the relationship between Se intake and telomere length in patients with diabetes has not been well studied. Therefore, this study aimed to investigate the relationship between dietary Se intake and telomere length in patients with diabetes. We extracted 878 participants with diabetes from the National Health and Nutrition Examination Survey database for 1990-2002. Dietary Se intake was assessed using the 24 h dietary recall method, and telomere length was measured using quantitative PCR. Generalised linear models were constructed to assess the relationship between dietary Se intake and telomere length. After controlling for the confounders, 1 μg increase in dietary Se intake in female patients with diabetes, and telomere length increased by 1·84 base pairs (β = 1·84 (95 % CI: 0·15, 3·53)), there was a line relationship between dietary Se intake and telomere length in female patients with diabetes and telomere length increased with increasing dietary Se intake within the range of 0-250 μg. The study demonstrates that dietary Se intake is significantly associated with telomere length only in the female population with diabetes in the USA. However, further prospective studies are required to confirm this finding.

Disordered serum essential element levels are associated with increased risk of kidney tumors

Essential elements play vital roles in the regulation of carcinogenesis. We aimed to investigate the relationship between essential elements and kidney tumors. This study included 72 healthy individuals and 100 kidney tumor patients. The concentrations of cobalt (Co), chromium (Cr), copper (Cu), iron (Fe), manganese (Mn), nickel (Ni), selenium (Se), and zinc (Zn) were determined by inductively coupled plasma mass spectrometry. The random forest model was used to evaluate the importance of each variable by using the randomForest package. The associations between essential elements and clinical tumor characteristics were examined by the Mann-Whitney U-test, and the log-rank test was used to assess the Kaplan-Meier curves. The levels of Co, Cr, Fe, Mn, Ni, and Zn in patients with kidney tumors were significantly lower. In the random forest model, the top two metallic features were Co and Zn. The Kaplan-Meier curve showed that patients with lower Co, Se, and Zn levels exhibited lower progression-free survival. In summary, this study gathered evidence that disordered essential elements are associated with kidney tumors and thus opens a new path to elucidate the etiology of kidney tumors from the perspective of environmental health and safety.

A concise review on the role of selenium for bone cancer applications

Cancer is one of the most challenging health problems in the world. Several clinical treatments have been developed, but all presenting several limitations. Among different types of cancer, bone cancer is less common, and limited new clinical treatment strategies have been proposed. Recently, a range of advanced materials has been investigated and applied for bone cancer treatment applications. However, due to the unique physiological properties of the bone tissue (a load-bearing tissue), the selection of the right type of material or the combination of suitable functional materials and base materials are critical. Selenium has been reported to present specific targeting inhibition effects on bone cancer without affecting the surrounding healthy tissue, revealing a huge potential for the development of new bone cancer treatment strategies. This paper presents a concise review on the use of selenium for bone cancer applications, discussing main synthesis methods, biocompatibility, and cytotoxicity aspects and the combination of selenium with a wide range of ceramics, metals, and polymers. Future perspectives and the novel concept of a dual-functional scaffold for both cancer treatment and new bone regeneration are also discussed.

The Role of Antioxidants in Cancer, Friends or Foes?

Consumption of dietary supplements by millions of people is increasing [1]. Between 64 to 81% of cancer patients and survivors use multivitamin supplements after the cancer diagnosis [2]. The use of antioxidants during cancer therapy has been a hot topic in medical science for the last 20 years without clear answers and recommendations. It seems that antioxidants are able to I) decrease the cancer formation risk by quenching ROS that are involved in cancer initiation and progression and II) assist in survival of cancer/precancer cells once the malignant transformation already occurred. Antioxidants were shown to assist cancer initiation, interfere with cancer treatment by reducing its efficacy and patient survival, and vice versa, there are reports of beneficial antioxidant effect during the cancer treatment.

Influence of the selenium level on overall survival in lung cancer

BACKGROUND

Although the results of studies in populations with low selenium status indicate an inverse correlation between body selenium levels and the risk of the lung cancer, the effect of this microelement on survival has not been studied.

MATERIALS AND METHODS

We performed a prospective study of 302 patients diagnosed with lung cancer in Szczecin, Poland. Selenium concentration in serum was measured at the time of diagnosis and before treatment. All patients were followed for a maximum of 80 months or until death. Vital status was obtained from the Polish National Death Registry.

RESULTS

Using Cox proportional hazard analysis, performed for all individuals with lung cancer, the hazard ratio (HR) for death from all causes was 1.25 (95% CI: 0.86-1.83, P = 0.99) for patients in the lowest tertile compared to those in the highest tertile of serum selenium levels. Among the patients with stage I disease this relationship was significant (HR-2.73; P = 0.01) for selenium level in tertile 1 (<57 μg/L) compared to tertile 3 (>69 μg/L, reference). The 80 months crude survival after diagnosis was 79.5% (95% CI: 68.5-92.4%) for individuals in the highest tertile and 58.1% (95% CI: 45.1-74.9%) for individuals in the lowest tertile with stage I lung cancer.

CONCLUSION

These results suggest that in patients undergoing treatment for stage I lung cancer, serum selenium levels at the time of diagnosis (>69 μg/L) may be associated with improved overall survival.

Selenium-doped hydroxyapatite biopapers with an anti-bone tumor effect by inducing apoptosis

Functional Se-HA/chitosan biopapers constructed with self-assembled Se-doped HA nanowires and chitosan have been reported and display high performances in in vitro/vivo anti-tumor studies.

Plasma selenoprotein P concentration and lung cancer risk: results from a case-control study nested within the Shanghai Men's Health Study

Selenoprotein P (SELENOP) is a major selenoenzyme in plasma and linked to antioxidant properties and possibly to lung cancer; however, supporting evidence is limited. We investigated the association between pre-diagnostic plasma SELENOP concentration and lung cancer risk in a case-control study of 403 cases and 403 individually matched controls nested within the Shanghai Men's Health Study. SELENOP concentration in pre-diagnostic plasma samples was measured by a sandwich enzyme-linked immunosorbent assay. Cases were diagnosed with lung cancer between 2003 and 2010. Multivariate conditional logistic regression was used to estimate odds ratios (OR) and the corresponding 95% confidence intervals (CI) for studying the association between plasma SELENOP concentration and lung cancer risk. Cases had slightly lower plasma SELENOP concentration than controls (4.3 ± 1.2 versus 4.4 ± 1.1 mg/l, P difference = 0.09). However, the multivariate analysis showed no association between plasma SELENOP concentration and lung cancer risk among all participants (OR = 1.08, 95% CI = 0.54-2.14 for quartile 4 versus quartile 1), or by smoking status or tumor aggressiveness. In contrast, although the number of cases was limited, plasma SELENOP concentration was positively associated with lung adenocarcinoma risk (OR = 5.38, 95% CI = 1.89-15.35 for tertile 3 versus tertile 1), but not with squamous cell lung carcinoma (OR = 1.69, 95% CI = 0.43-6.70). Our study of adult men living in selenium non-deficient areas in China provides little support for the inverse association between pre-diagnostic plasma SELENOP concentration and lung cancer risk. Our finding of a positive association with risk of lung adenocarcinoma needs to be interpreted with caution.

When Is Enough, Enough? When Are More Observational Epidemiologic Studies Needed to Resolve a Research Question: Illustrations Using Biomarker-Cancer Associations

BACKGROUND

Research reproducibility is vital for translation of epidemiologic findings. However, repeated studies of the same question may be undertaken without enhancing existing knowledge. To identify settings in which additional research is or is not warranted, we adapted research synthesis metrics to determine number of additional observational studies needed to change the inference from an existing meta-analysis.

METHODS

The fail-safe number (FSN) estimates number of additional studies of average weight and null effect needed to drive a statistically significant meta-analysis to null (P ≥ 0.05). We used conditional power to determine number of additional studies of average weight and equivalent heterogeneity to achieve 80% power in an updated meta-analysis to detect the observed summary estimate as statistically significant. We applied these metrics to a curated set of 98 meta-analyses on biomarkers and cancer risk.

RESULTS

Both metrics were influenced by number of studies, heterogeneity, and summary estimate size in the existing meta-analysis. For the meta-analysis on Helicobacter pylori and gastric cancer with 15 studies [OR = 2.29; 95% confidence interval (CI), 1.71-3.05], FSN was 805 studies, supporting futility of further study. For the meta-analysis on dehydroepiandrosterone sulfate and prostate cancer with 7 studies (OR = 1.29; 95% CI, 0.99-1.69), 5 more studies would be needed for 80% power, suggesting further study could change inferences.

CONCLUSIONS

Along with traditional assessments, these metrics could be used by stakeholders to decide whether additional studies addressing the same question are needed.

IMPACT

Systematic application of these metrics could lead to more judicious use of resources and acceleration from discovery to population-health impact.

Developmental selenium exposure and health risk in daily foodstuffs: A systematic review and meta-analysis

Selenium (Se) is a trace mineral and an essential nutrient of vital importance to human health in trace amounts. It acts as an antioxidant in both humans and animals, immunomodulator and also involved in the control of specific endocrine pathways. The aim of this work is to provide a brief knowledge on selenium content in daily used various foodstuffs, nutritional requirement and its various health consequences. In general, fruits and vegetables contain low content of selenium, with some exceptions. Selenium level in meat, eggs, poultry and seafood is usually high. For most countries, cereals, legumes, and derivatives are the major donors to the dietary selenium intake. Low level of selenium has been related with higher mortality risk, dysfunction of an immune system, and mental failure. Selenium supplementation or higher selenium content has antiviral outcomes and is necessary for effective reproduction of male and female, also decreases the threat of chronic disease (autoimmune thyroid). Generally, some advantages of higher content of selenium have been shown in various potential studies regarding lung, colorectal, prostate and bladder cancers risk, nevertheless results depicted from different trials have been diverse, which perhaps indicates the evidence that supplementation will merely grant advantage if the intakes of a nutrient is deficient. In conclusion, the over-all people should be advised against the usage of Se supplements for prevention of cardiovascular, hepatopathies, or cancer diseases, as advantages of Se supplements are still ambiguous, and their haphazard usage could result in an increased Se toxicity risk. The associations among Se intake/status and health, or disease risk, are complicated and need exposition to notify medical practice, to improve dietary recommendations, and to develop adequate communal health guidelines.

Trace element contents in toenails are related to regular physical activity in older adults

The aim was to assess the trace element contents in toenails of older adults and its association with regular physical activity. Cross-sectional multicentre study in Spain, collecting data from a random sample of 380 participants (54% female) aged 55–80 years (men) and 60–80 years (women) with no previously documented cardiovascular disease. Physical activity performed was measured using the Minnesota Leisure-time Physical Activity Questionnaire. The 25 most inactive and 25 most active individuals for each sex were selected for this study (final sample n = 100). Anthropometric measurements were performed and toenail samples collected for calcium (Ca), chromium (Cr), iron (Fe), cobalt (Co), nickel (Ni), zinc (Zn), selenium (Se) and mercury (Hg) analysis. Significant differences between sexes were reported in Ca concentrations, women having lower concentrations than men. No differences were reported in trace element contents between active and inactive men. Active women showed higher Ca, Cr, Fe, Co, and Zn and lower Hg contents than their inactive peers (all p<0.05). Inactive women showed lower Ca and Co levels (735.0 mg/kg and 4.5 μg/kg, respectively) than inactive men (1170.0 mg/kg and 7.9 μg/kg, respectively). Active women had lower Ca and higher levels of Cr (936.0 mg/kg and 1230.0 μg/kg, respectively) than active men (1070.0 mg/kg and 522.0 μg/kg, respectively). The present data added new information on the element contents in toenails of healthy Spanish older adults. The concentration of trace elements was similar in both sexes except for Ca which were lower in women. The trace element contents in women’s toenails, but not in men, were markedly influenced by physical activity, with higher levels of Ca and Fe and lower Hg among active females.

Inverse Association between Dietary Intake of Selected Carotenoids and Vitamin C and Risk of Lung Cancer

While diets rich in fruit and vegetables appear to reduce lung cancer risk, the evidence for individual carotenoid and vitamin intakes has been judged too limited to reach firm conclusions. Data from a case-control study of lung cancer (Montreal, QC, Canada, 1996-2002) were used to investigate the role of dietary intakes of β-carotene, α-carotene, β-cryptoxanthin, lutein/zeaxanthin, lycopene, and vitamin C in lung cancer risk. In-person interviews elicited dietary information from 1,105 incident cases and 1,449 population controls. Usual frequency of consumption of 49 fruits and vegetables 2 years prior to diagnosis/interview was collected. Odds ratios (ORs) and 95% confidence intervals (CIs) between intake variables and lung cancer were estimated using logistic or polytomous regression, adjusting for potential confounding factors including a detailed smoking history. ORs associated with upper versus lower tertiles of intake were 0.66 (95% CI = 0.51-0.84) for β-carotene, 0.70 (95% CI = 0.55-0.90) for α-carotene, 0.65 (95% CI = 0.51-0.84) for β-cryptoxanthin, 0.75 (95% CI = 0.59-0.95) for lycopene, and 0.74 (95% CI = 0.58-0.96) for vitamin C. ORs suggestive of a protective effect were found for elevated intakes of β-carotene, α-carotene, β-cryptoxanthin, and lycopene in male heavy smokers and of vitamin C in female heavy smokers. Selected antioxidants were also associated with a lower risk of lung cancer in female moderate smokers, and of squamous cell carcinoma, adenocarcinoma, and small cell carcinoma. These results suggest that several dietary antioxidants found in common food sources may protect against lung cancer, even among heavy smokers.

Association between selenium intake and the risk of pancreatic cancer: a meta-analysis of observational studies

Quantification of the association between the intake of selenium and risk of pancreatic cancer is still conflicting. Thus, we conducted a meta-analysis to summarize the evidence from epidemiological studies of selenium intake with the risk of pancreatic cancer. Pertinent studies were identified by a search of PubMed and Web of Knowledge to July 2016. The random-effect model was used. Sensitivity analysis and publication bias were conducted. Data from six studies including 1424 pancreatic cancer cases were used in this meta-analysis. Pooled results suggested that highest selenium intake amount compared with lowest amount was significantly associated with the risk of pancreatic cancer [summary relative risk (RR)=0.659, 95% confidence interval (CI)=0.489-0.889, I²=47.6%]. The associations were significant both in case-control studies [RR=0.618, 95%CI=0.399-0.956, I²=59.1%] and Americas [RR=0.570, 95%CI=0.357-0.909, I²=65.6%]. No publication bias was found. Our analysis suggested that the higher intake of selenium might reduce the risk of pancreatic cancer.

Long-term mortality patterns in a residential cohort exposed to inorganic selenium in drinking water

Selenium (Se) is a metalloid of considerable nutritional and toxicological importance in humans. To date, limited epidemiologic evidence exists about the health effects of exposure to this trace element in drinking water. We investigated the relationship between Se levels in water and mortality in the municipality of Reggio Emilia, Italy, where high levels of Se were previously observed in drinking water. From 1974 to 1985, 2065 residents consumed drinking water with Se levels close to the European standard of 10μg/l, in its inorganic hexavalent form (selenate). Follow-up was conducted for the years 1986-2012 in Reggio Emilia and a lesser exposed comparison group of around 100,000 municipal residents, with comparable socio-demographic characteristics. Overall mortality from all causes, cardiovascular disease and cancer showed little evidence of differences. However, excess rate ratios were seen for some site specific cancers such as neoplasms of buccal cavity and pharynx, urinary tract, lymphohematopoietic tissue, melanoma, and two neurodegenerative diseases, Parkinson's disease and amyotrophic lateral sclerosis. Excess mortality in the exposed cohort for specific outcomes was concentrated in the first period of follow-up (1986-1997), and waned starting 10 years after the high exposure ended. We also found lower mortality from breast cancer in females during the first period of follow-up. When we extended the analysis to include residents who had been consuming the high-selenium drinking water for a shorter period, mortality rate ratios were also increased, but to a lesser extent. Overall, we found that the mortality patterns related to long-term exposure to inorganic hexavalent selenium through drinking water were elevated for several site-specific cancers and neurodegenerative disease.

How reliable are randomised controlled trials for studying the relationship between diet and disease? A narrative review

Large numbers of randomised controlled trials (RCT) have been carried out in order to investigate diet-disease relationships. This article examines eight sets of studies and compares the findings with those from epidemiological studies (cohort studies in seven of the cases). The studies cover the role of dietary factors in blood pressure, body weight, cancer and heart disease. In some cases, the findings from the two types of study are consistent, whereas in other cases the findings appear to be in conflict. A critical evaluation of this evidence suggests factors that may account for conflicting findings. Very often RCT recruit subjects with a history of the disease under study (or at high risk of it) and have a follow-up of only a few weeks or months. Cohort studies, in contrast, typically recruit healthy subjects and have a follow-up of 5-15 years. Owing to these differences, findings from RCT are not necessarily more reliable than those from well-designed prospective cohort studies. We cannot assume that the results of RCT can be freely applied beyond the specific features of the studies.

Dietary selenium intake and mortality in two population-based cohort studies of 133 957 Chinese men and women

OBJECTIVE

To investigate the potential influence of dietary Se intake on mortality among Chinese populations.

DESIGN

We prospectively evaluated all-cause, CVD and cancer mortality risks associated with dietary Se intake in participants of the Shanghai Women's Health Study (SWHS) and the Shanghai Men's Health study (SMHS). Dietary Se intake was assessed by validated FFQ during in-person interviews. Cox proportional hazards models were used to calculate hazard ratios (HR) and 95 % CI.

SETTING

Urban city in China.

SUBJECTS

Chinese adults (n 133 957).

RESULTS

During an average follow-up of 13·90 years in the SWHS and 8·37 years in the SMHS, 5749 women and 4217 men died. The mean estimated dietary Se intake was 45·48 μg/d for women and 51·34 μg/d for men, respectively. Dietary Se intake was inversely associated with all-cause mortality and CVD mortality in both women and men, with respective HR for the highest compared with the lowest quintile being 0·79 (95 % CI 0·71, 0·88; P trend<0·0001) and 0·80 (95 % CI 0·66, 0·98; P trend=0·0268) for women, and 0·79 (95 % CI 0·70, 0·89; P trend=0·0001) and 0·66 (95 % CI 0·54, 0·82; P trend=0·0002) for men. No significant associations were observed for cancer mortality in both women and men. Results were similar in subgroup and sensitivity analyses.

CONCLUSIONS

Dietary Se intake was inversely associated with all-cause and cardiovascular mortality in both sexes, but not cancer mortality.

Dietary mineral intake and lung cancer risk: the Rotterdam Study

Objective

Limited data are available on the role of mineral intake in the development of lung cancer (LC). We investigated whether dietary calcium, copper, iron, magnesium, selenium and zinc intake were associated with LC risk.

Methods

We analyzed data from 5435 participants of the Rotterdam Study, a prospective population-based cohort study among subjects aged 55 years and older. At baseline (1990–1993), diet was measured by a validated food frequency questionnaire. LC events were diagnosed on the basis of pathology data and medical records. Hazard ratios (HRs) on LC for energy-adjusted mineral intake were calculated using Cox regression models while adjusting for potential confounders.

Results

During a follow-up period of 22 years, we identified 211 incident cases of LC. A higher zinc intake was associated with 42 % reduction in risk of LC (top tertile vs. first tertile: HR 0.58, 95 % CI 0.35; 0.94, P-for trend = 0.039). Similarly, high intake of iron was associated with reduced risk of LC (top tertile vs. first tertile: HR 0.58, 95 % CI 0.37; 0.92, P-for trend = 0.021). There was no association between dietary intake of calcium, copper, magnesium and selenium and LC risk.

Conclusions

Our results suggest that dietary zinc and iron intake are associated with reduced risk of LC. No evidence was found for an association between calcium, copper, magnesium and selenium intake and LC risk.

Electronic supplementary material

The online version of this article (doi:10.1007/s00394-016-1210-4) contains supplementary material, which is available to authorized users.

Selenoproteins and Cancer Prevention

The discovery of multiple selenoproteins has raised tantalizing questions about their role in maintaining normal cellular function. Unfortunately, many of these remain inadequately investigated. While they have a role in maintaining redox balance, other functions are becoming increasingly recognized. As the roles of these selenoproteins are further characterized, a better understanding of the true physiological significance of this trace element will arise. This knowledge will be essential in defining optimum intakes to achieve cellular homeostasis in order to optimize health, including a reduction in cancer, for diverse populations. Human variation in the response to selenium likely reflects significant interactions between the type and amounts of selenium consumed with the genome and a host of environmental factors including the totality of the diet, as discussed in this review.

Dietary intake and arsenic methylation in a U.S. population

Millions of people worldwide are exposed to arsenic-contaminated drinking water, and ingestion of inorganic arsenic (InAs) has been associated with increased risks of cancer. The primary metabolic pathway of ingested InAs is methylation to monomethyl arsenic (MMA) and dimethyl arsenic (DMA). However, people vary greatly in the degree to which they methylate InAs, and recent evidence suggests that those who excrete high proportions of ingested arsenic as MMA are more susceptible than others to arsenic-caused cancer. To date, little is known about the factors that determine interindividual differences in arsenic methylation. In this study, we assessed the effect of diet on arsenic metabolism by measuring dietary intakes and urinary arsenic methylation patterns in 87 subjects from two arsenic-exposed regions in the western United States. Subjects in the lower quartile of protein intake excreted a higher proportion of ingested InAs as MMA (14.6 vs. 11.6%; p = 0.01) and a lower proportion as DMA (72.3 vs. 77.0%; p = 0.01) than did subjects in the upper quartile of protein intake. Subjects in the lower quartile of iron, zinc, and niacin intake also had higher urinary percent MMA and lower percent DMA levels than did subjects with higher intakes of these nutrients. These associations were also seen in multivariate regression analyses adjusted for age, sex, smoking, and total urinary arsenic. Given the previously reported links between high percent MMA and increased cancer risks, these findings are consistent with the theory that people with diets deficient in protein and other nutrients are more susceptible than others to arsenic-caused cancer.