Erythrocyte selenium and breast cancer risk

Association between selenium intake and breast cancer risk: results from the Women's Health Initiative

PURPOSE

It has been hypothesized that selenium (Se) can prevent cancer, and that Se deficiency may be associated with an increased risk of breast cancer. However, findings from epidemiological studies have been inconsistent. The objective of this study was to assess the association between Se intake and risk of breast cancer in the Women's Health Initiative (WHI).

METHODS

This study included 145,033 postmenopausal women 50-79 years who completed baseline questionnaires between October 1993 and December 1998, which addressed dietary and supplemental Se intake and breast cancer risk factors. The association between baseline Se intake and incident breast cancer was examined in Cox proportional hazards analysis.

RESULTS

During a mean follow-up of 15.5 years, 9487 cases of invasive breast cancer were identified. Total Se (highest versus lowest quartile: HR 1.00, 95% CI 0.92-1.09, P_trend = 0.66), dietary Se (highest versus lowest quartile: HR 0.99, 95% CI 0.89-1.08, P_trend = 0.61), and supplemental Se (yes versus no: HR 0.99, 95% CI 0.95-1.03) were not associated with breast cancer incidence.

CONCLUSIONS

This study indicates that Se intake is not associated with incident breast cancer among postmenopausal women in the United States. Further studies are needed to confirm our findings by using biomarkers such as toenail Se to reduce the potential for misclassification of Se status.

Responses of trace elements to aerobic maximal exercise in elite sportsmen

Trace elements are chemical elements needed in minute quantities for the proper growth, development, and physiology of the organism. In biochemistry, a trace element is also referred to as a micronutrient. Trace elements, such as nickel, cadmium, aluminum, silver, chromium, molybdenum, germanium, tin, titanium, tungsten, scandium, are found naturally in the environment and human exposure derives from a variety of sources, including air, drinking water and food. The Purpose of this study was investigated the effect of aerobic maximal intensity endurance exercise on serum trace elements as well-trained individuals of 28 wrestlers (age (year) 19.64±1.13, weight (Kg) 70.07 ± 15.69, height (cm) 176.97 ± 6.69) during and after a 2000 meter Ergometer test protocol was used to perform aerobic (75 %) maximal endurance exercise. Trace element serum levels were analyzed from blood samples taken before, immediately after and one hour after the exercise. While an increase was detected in Chromium (Cr), Nickel (Ni), Molybdenum (Mo) and Titanium (Ti) serum levels immediately after the exercise, a decrease was detected in Aluminum (Al), Scandium (Sc) and Tungsten (W) serum levels. Except for aluminum, the trace elements we worked on showed statistically meaningful responses (P < 0.05 and P < 0.001). According to the responses of trace elements to the exercise showed us the selection and application of the convenient sport is important not only in terms of sportsman performance but also in terms of future healthy life plans and clinically.

Abnormal blood levels of trace elements and metals, DNA damage, and breast cancer in the state of Kuwait

This study aims at investigating the blood level of Cu, Zn, Se, and Cd in breast cancer patients and the association between such level and the frequency of micronucleated lymphocytes. Fifty stage I breast cancer patients were recruited for this study at the time of diagnosis and before receiving any treatment or surgery. The control group consisted of 150 normal females matched to the patients for age (± 5 years). The whole blood level of Cu, Zn, Se, and Cd was determined using spectrophotometry. The frequency of micronucleated lymphocytes in the blood was determined using the cytokinesis-block micronucleus assay. The level of Cu, Zn, and Se was significantly lower (p = 0.0006, <0.0001, and <0.0001, respectively) in breast cancer patients, as compared to controls. The level of Cd was significantly (p < 0.0001) higher in the patients, as compared to controls. The frequency of lymphocytes with one micronucleus was significantly (p < 0.0001) higher in the patients, as compared to controls. In breast cancer patients, the frequency of micronucleated lymphocytes showed different associations with different levels of these trace elements. High Cd, low Zn, low Se, and both high and low Cu levels were significantly associated with micronucleus formation in lymphocytes. A similar association was found in the normal control group only in relation to high Se and Cd levels. Breast cancer patients seem to have abnormal levels of Cu, Zn, Se, and Cd, and such abnormality is associated with micronucleus formation in lymphocytes.

Levels of zinc, selenium, calcium, and iron in benign breast tissue and risk of subsequent breast cancer

Previous studies that have assessed breast cancer in relation to zinc, selenium, calcium, and iron have yielded inconsistent results but have not measured breast tissue levels. In a case-control study involving 252 matched pairs nested in a cohort of 9,315 women with benign breast disease, we investigated these associations by directly measuring elemental levels in breast tissue using X-ray fluorescence spectroscopy. Quintile analyses revealed positive associations of breast cancer, of borderline statistical significance, with zinc [highest versus lowest quintile: odds ratio (OR), 1.37; 95% confidence limit (95% CL), 0.91, 2.05; P(trend) = 0.04], iron (highest versus lowest quintile: OR, 1.58; 95% CL, 1.02, 2.44; P(trend) = 0.07), and calcium (highest versus lowest quintile: OR, 1.46; 95% CL, 0.98, 2.17; P(trend) = 0.14), but little association with selenium (highest versus lowest quintile: OR, 1.10; 95% CL, 0.72, 1.68; P(trend) = 0.76). The associations were weakened by mutual adjustment. Furthermore, after stratification by menopausal status, the positive association between iron and breast cancer was confined to postmenopausal women (highest versus lowest quintile: OR, 2.77; 95% CL, 1.25, 6.13; P(trend) = 0.008), whereas the associations for zinc, calcium, and selenium did not differ by menopausal stratum. In conclusion, our data raise the possibility that relatively high levels of zinc, iron, and calcium in benign breast tissue may be associated with a modest increase in risk of subsequent breast cancer.

Trace elements and cancer risk: a review of the epidemiologic evidence

Worldwide, there are more than 10 million new cancer cases each year, and cancer is the cause of approximately 12% of all deaths. Given this, a large number of epidemiologic studies have been undertaken to identify potential risk factors for cancer, amongst which the association with trace elements has received considerable attention. Trace elements, such as selenium, zinc, arsenic, cadmium, and nickel, are found naturally in the environment, and human exposure derives from a variety of sources, including air, drinking water, and food. Trace elements are of particular interest given that the levels of exposure to them are potentially modifiable. In this review, we focus largely on the association between each of the trace elements noted above and risk of cancers of the lung, breast, colorectum, prostate, urinary bladder, and stomach. Overall, the evidence currently available appears to support an inverse association between selenium exposure and prostate cancer risk, and possibly also a reduction in risk with respect to lung cancer, although additional prospective studies are needed. There is also limited evidence for an inverse association between zinc and breast cancer, and again, prospective studies are needed to confirm this. Most studies have reported no association between selenium and risk of breast, colorectal, and stomach cancer, and between zinc and prostate cancer risk. There is compelling evidence in support of positive associations between arsenic and risk of both lung and bladder cancers, and between cadmium and lung cancer risk.

The Role of Nutrition in the Prevention of Breast Cancer

Nutrition has been widely studied as a leading environmental factor in the prevention of breast cancer (BC). Despite the challenges in relating consumption of specific nutrients to BC risk, particularly in the context of a total diet, many investigators have contributed valuable information. Dietary fat has received the most attention and also created the most uncertainty. Specific types of fat, particularly monounsaturated fat and the ratio of omega-3 to omega-6 fatty acids, demonstrate more potential to influence BC risk. A wide variety of other dietary factors have been studied in relation to BC including total energy, dietary fiber, alcohol, micronutrients, phytochemicals, specific foods, and food constituents. Results of epidemiological studies relating consumption of these dietary factors to BC have increased the knowledge base that provides rationale for various nutritional strategies to contribute to BC prevention.

Effects of selenite on estrogen receptor-alpha expression and activity in MCF-7 breast cancer cells

To determine whether selenite has estrogen-like activities, the effects of this compound on estrogen receptor-alpha (ER-alpha) and other estrogen-regulated genes were measured in the human breast cancer cell line MCF-7. Treatment of cells with 1 uM of sodium selenite resulted in a 40% decrease in the amount of estrogen receptor-alpha and in a parallel decrease of 40% in ER-alpha mRNA. Progesterone receptor concentration increased 2.6-fold and pS2 mRNA increased 2.4-fold after selenite treatment. The induction of progesterone receptor and pS2 was blocked by the anti-estrogen ICI-182,780. In transient co-transfection experiments of Wild-type ER-alpha and an estrogen response element-reporter construct, selenite stimulated CAT activity. In binding assays, selenite blocked the binding of estradiol to ER-alpha (K(i) = 23 +/- 17 nM, n = 3) suggesting that this compound interacts with the hormone binding domain of the receptor. To determine whether interaction of selenite with the hormone binding domain results in receptor activation, COS-1 cells were transiently co-transfected with the chimeric receptors GAL-ER, which contains the hormone binding domain of ER-alpha and the DNA binding domain of the transcription factor GAL4, and a GAL4-responsive CAT reporter gene. Treatment of cells with estradiol or selenite resulted in a three- to five-fold increase in CAT activity. The effects of selenite on the chimeric receptor were blocked by the antiestrogen, suggesting that selenite activates ER-alpha through an interaction with the hormone binding domain of the receptor. Transfection assays with ER-alpha mutants identified C381, C447, H524, and N532 as interaction sites of selenite with the hormone binding domain.

A case-control study on selenium, zinc, and copper in plasma and hair of subjects affected by breast and lung cancer

The purpose of our study was to investigate the relationship between plasma and hair levels of Se, Zn, and Cu, and cancer. We selected a total of 66 patients affected by either breast (38) or lung (28) cancer. They entered into the study at the onset of disease, and before any chemical or radiotherapy. Controls were randomly selected among healthy people and were matched for sex, age, smoking habits, and residence. In the group of breast cancer, a significant decrease in hair Se was found compared to controls (p < 0.01), whereas plasma Se was only slightly decreased. No difference between cases and controls was detected in both hair and plasma levels of Zn and Cu. Subjects who developed lung cancer were significantly lower in hair Zn (p < 0.05) and Cu (p < 0.01) than controls, whereas there was no difference with regard to Se. In addition, plasma Cu of these patients was increased as compared to controls.

Nutrition and breast cancer

Epidemiologic evidence on the relation between nutrition and breast cancer is reviewed. After several decades of study, many aspects of the role of diet in breast cancer etiology are still unclear. Results from large prospective studies do not support the concept developed from animal and ecologic evidence that dietary fat intake in mid-life is associated with breast cancer risk. Thus, if fat intake is relevant to breast cancer, it is probably only at extremely low fat intakes or during early life. An emerging hypothesis that higher energy intake and growth rate in childhood and adolescence increases risk deserves further study. The possibility that diets rich in olive oil may be protective is also intriguing. Considerable evidence suggests that low intake of vegetables modestly increases the risk of breast cancer; however, the nutrients responsible remain elusive. The positive relation of alcohol intake with breast cancer risk has been seen repeatedly, and recently has been buttressed by studies showing that moderate alcohol intake increases estrogen endogenous levels. Advice to increase vegetable intake and limit alcohol consumption would probably have a modest, at best, effect on breast cancer risk. Future studies of the relation of nutrition during early life to subsequent breast cancer risk are needed.

Antioxidant micronutrients and breast cancer

We reviewed epidemiologic evidence on the relationship between four antioxidant micronutrients (vitamin A, vitamin C, vitamin E, and selenium) and breast cancer risk. Available data support a modest protective effect of vitamin A, although more studies are needed to examine further this association and to assess the relative contributions of preformed vitamin A (retinol) and carotenoids. In addition, the possibility that some other component of vitamin A-rich foods may account for this observed association should be explored. Data on the relationship between vitamins C and E and breast cancer risk are limited and inconsistent, and further information is necessary. A substantial body of evidence indicates a lack of any appreciable effect of selenium intake on breast cancer risk, at least within the range of human diets. Future observational studies should ideally be prospective in design, as prospective studies are less prone to selection and recall bias than are case-control studies, and should address methodologic issues such as confounding by other micronutrients and appropriate storage conditions of blood specimens. Although hypotheses relating micronutrient intake to risk of breast cancer should be tested in randomized trials, ethical and logistical constraints make these studies difficult to perform.

Selenium and the risk of postmenopausal breast cancer in the DOM cohort

Selenium has been claimed to have chemo-preventive properties. However, data showing that in humans selenium levels are already decreased prior to diagnosis of breast cancer were not available. Such information is mandatory before oral selenium supplementation in the primary prevention of (breast) cancer in humans is acceptable. This question of a 'preventive-potential' of selenium was evaluated in a case-control study nested in a cohort, because this design allows determination of the time-order of preceding selenium levels and subsequent cancer risk. The cohort consisted of 5577 women aged 55-70 years from the DOM project, a population based breast cancer screening program in the Netherlands. Instrumental Neutron Activation Analysis was used to measure the selenium content of toenail clippings. The 69 cases of breast cancer found during follow-up after screening. represent 'recent' tumours since all women had a negative screening mammogram 3-5 years previously. No decreased selenium levels, as measured in nail clippings from the big toes, could be detected in cases-to-be, either when compared to 4 age matched controls per case or when compared with a random control group drawn from the entire cohort. On the contrary, a tendency for slightly higher selenium levels among 'future' cancer cases was observed. As to the sensitivity of detecting differences in selenium by nail clippings, lower selenium could be detected in nails of current smokers. The smoking-related decrease in nail selenium level was of the same order as the differences between breast cancer cases and controls, but was independent of the breast cancer risk.(ABSTRACT TRUNCATED AT 250 WORDS)

The iodine-selenium connection: its possible roles in intelligence, cretinism, sudden infant death syndrome, breast cancer and multiple sclerosis

Several diseases and disorders display spatial patterns that suggest the involvement of both selenium and iodine deficiencies, or excesses, in their etiologies. It is suggested that many of these similarities in geographical distribution occur because both elements influence thyroid hormone metabolism.

Aging and cancer: plasma antioxidants and lipid peroxidation in young and aged breast cancer patients

The relationship between aging and cancer is complex because the intrication takes place at the cell, the organism and the environment levels. On the other hand, carcinogenesis is a multi-step process, and different mechanisms may be involved in each step. For example, oxidants and antioxidants may play a different role depending upon the phase considered. Tumors in older patients are generally described as slow growing. The difference in tumor aggressiveness between young and older patients is especially obvious in breast cancer patients. The age specificity of some breast risk factors suggests that breast cancer which has been diagnosed in an aged woman was induced late in her life. We address the question whether the characteristics of a senescent organism with regards to oxidant-antioxidant status could be causally related to the slow evolution of tumors in old patients.

Selenium in human mammary carcinogenesis: a case-cohort study

In a prospective study conducted on the island of Guernsey a cohort of 5162 ostensibly healthy women was enrolled between 1967 and 1976. Blood samples were drawn from each participant, who also completed a questionnaire, which provided information on established risk indicators in human mammary carcinogenesis. Plasma selenium levels were measured in 46 breast cancer cases diagnosed a mean of 11 (S.D. 4) years after entry into the study cohort and in an age-stratified sample of 138 women drawn from the study base. Plasma selenium level in the cases was 109 (28) micrograms/l and in the base sample 103 (22) micrograms/l (95% confidence interval for the overall difference, -2 to 14 micrograms/l). The adjusted relative risk of developing breast cancer in the different quartiles of the selenium distribution was 0.80, 0.79, 0.72 and 1.00, respectively. Thus, in the present study selenium was not a strong indicator of human breast cancer risk.

Antioxidants in female breast cancer patients

Blood levels of selenium, zinc, copper, and vitamins E and C were measured in 48 cases and 50 controls from a hospital-based case-control study bearing on breast cancer risk factors in Montpellier (France). Cellular levels of selenium and vitamins E and C were also evaluated in most of the subjects. We found that the blood and cellular levels of these antioxidants were overall higher in cases than in controls, significantly for serum zinc, plasma, and leukocyte vitamin E. The statistical significance of the difference between case and control serum Cu crude levels disappeared after adjustment for metabolically related variables. The difference was borderline significant for leukocyte vitamin C. These results were slightly modified when vitamin pill users were excluded from case and control samples. The serum zinc odds ratios computed after adjustment for related variables were significantly elevated (2.53, confidence interval: 1.34-4.78, for the highest tertile) as were those computed previously for pooled plasma vitamin E levels in a joint study.

Selenium: clinical significance and analytical concepts

Selenium is an essential trace element in humans and animals. Its only established function in humans is the antioxidant activity of glutathione peroxidase, a selenoenzyme. Severe prolonged deficiency may cause a fatal cardiomyopathy. Iatrogenic causes of selenium deficiency include parenteral and enteral nutrition. Low plasma selenium is also found in malabsorption, cystic fibrosis, rheumatoid arthritis, neoplasia, and other varied clinical disorders. Death has resulted from a single massive ingestion of selenium, while chronic excessive intake causes skin, nail, and hair pathology. Extreme geographical variation in population blood and urine selenium levels and a marked age-specific variation in population reference intervals are important factors in understanding selenium nutrition. Nutritional requirements, biological availability, and metabolism are discussed in relation to geographical, age, and method variability. Sampling, processing procedures, and methods for selenium quantitation are reviewed. Selenium content in different biological matrices and reference values for pediatric, adult, and obstetric populations are provided.

Serum selenium concentration associated with risk of cancer

The association between serum selenium concentration and risk of cancer was studied in a nested case control study. Case control pairs came from a population of 9364 people examined in 1979. During the six year follow up, 60 men and women aged between 20-54 at the time of blood sampling, who had been free of malignant disease, developed cancer. The mean serum selenium concentration of 1.56 mumol/l (123.2 micrograms/l) in patients was not significantly different from that in controls (1.63 mumol/l (128.7 micrograms/l]. The difference in mean selenium concentration was largest and most significant for haematological malignancies alone. The difference in selenium concentrations in cases of fatal cancer compared with controls was significant (p less than 0.01). The risk of developing adenocarcinomas does not seem to be influenced by serum selenium concentration.