Recent Developments

1. Selenium and Human Health - Summary
2. Selenium and Human Health - Latest Studies
3. Selenium in Food: Studies on Grains and Fish
4. Studies on Selenium in China

 

2. SELENIUM & HUMAN HEALTH - LATEST STUDIES

 

1. Alexander, J., " Selenium ", Novartis Foundation Symposium (CIBA formerly), Volume 282, 2007.

Selenium occurs as inorganic selenite or selenate and in organic forms in plants and other organisms used for food. The human forms of protein selenium consist of 25 seleno proteins. In seleno proteins, selenium occurs as seleno cysteine. Seleno proteins, such as seleno protein P, work as a transport of selenium between the liver and other organs. Selenium in the form of seleno methionine can also unspecifically substitute for methionine in other proteins. No specific deficiency condition has been described in humans. The etiology of Keshan disease, a juvenile heart muscle disease (cardiomyopathy), is a combination of coxsackie virus and low selenium . Selenium status has been linked to the incidence of cancer and other diseases. Excess selenium can produce selenosis in humans affecting liver, skin, nails, and hair. Recommended intake and upper tolerable levels are 40-55 and 300 microgram/day. A better chemical characterization of selenium compounds in foods and in particular supplements, as well as knowledge on the apparent differences in biological activity between selenium compounds, both with respect to nutrition, disease protection and adverse effects, are needed. Supplementation studies should in addition to possible beneficial effects also focus on the possibility of adverse effects.

2. Stranges, S., et al., "Effects of long-term selenium supplementation on the incidence of type 2 diabetes: a randomized trial", Annals of Internal Medicine, Volume 147(4), August 2007.

Findings from animal models suggest that selenium supplementation improves glucose metabolism. This study examined the effect of long-term selenium supplementation on the incidence of type 2 diabetes in areas of low selenium consumption of the eastern USA. Oral administration of selenium (200 ug/day or placebo. During an average follow up of 7.7 years, the incidence of type 2 diabetes developed at a rate of 12.6 cases per 1000 person years for selenium recipients and for placebo recipients 8.4 cases per 1000 person years. The lack of benefit of selenium supplementation on the incidence of type 2 diabetes persisted in analyses stratified by age, sex, body mass index, and smoking status. Conclusion is that selenium supplementation does not seem to prevent type 2 diabetes, and it may increase risk for the disease.

3. Silvera, S.A.N., Rohan, T.E., "Trace elements and cancer risk: A review of the epidemiological evidence", Cancer Causes and Control, Volume 18(1), February 2007.

Worldwide, there are more than 10 million new cancer cases each year, and cancer is the cause of approximately 12% of all deaths. Trace elements such as selenium , zinc, arsenic, cadmium and nickel, are found naturally in the environment and human exposures to them are potentially modifiable as the sources include air, drinking water, and food. The article reviewed the association between each of the trace elements and the 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. 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.

4. Gailer, J., "Arsenic- selenium and mercury- selenium bonds in biology", Coordination Chemistry Reviews, Volume 251(1-2), January 2007.

When rabbits are simultaneously injected with arsenite and selenate, or mercuric chloride and selenate , compounds with As- Se and Hg- Se bonds are formed in the bloodstream. The combined application of liquid chromatography-inductively coupled plasma atomic emission spectrometry (ICP-AES) and X-ray absorption spectroscopy (XAS) has revealed the molecular structure of these toxicologically important compounds. The glutathione-driven formation of these compounds in the blood stream fundamentally links the metabolism of the environmental pollutants mercuric mercury and arsenite with that of the essential ultra-trace element selenium , which establishes a feasible mechanism by which the chronic low-level exposure of various human populations to these toxic metals and metalloid compounds is linked to human diseases, including cancer and neurodegenerative diseases.

5. Thomson, C.D., "Assessment of requirements for selenium and adequacy of selenium status: A review", European Journal of Clinical Nutrition, Volume 58(3), 2004.

The review concluded that the minimum requirement for selenium is that which prevents the deficiency disease, Keshan disease. The recommended intakes of selenium have been calculated from the requirement for optimum plasma glutathione peroxidase (GPx) activity that must, because of the hierarchy of seleno proteins, also take account of the amounts need for normal levels of other biologically necessary selenium compounds. Whether optimal health depends upon maximization of the GPx or other seleno proteins, however, has yet to be resolved, and the consequences of less than maximal GPx activities or mRNA levels need investigation. Intakes, higher than recommended intakes, and plasma selenium concentrations that might be protective for cancer or result in other additional health benefits, have been proposed. There is an urgent need for more large-scale data on which to base more reliable estimates for intakes and plasma selenium levels that are protective.

6. Whanger, P.D., " Selenium and its relationship to cancer: An update", British Journal of Nutrition, Volume 91(1), 2004.

Seleno methionine ( Se met) is the major seleno -compound in cereal grains and enriched yeast where as Se -methylselenocysteine ( Se MCYS) is the major seleno -compound in Se -accumulator plants and some plants of economic importance such as garlic and broccoli. Blood or plasma levels of selenium are usually lower in patients with cancer than those without this disorder, but inconsistent results have been found with toenail- Se values and the incidence of cancer. There have been eight trials with human subjects conducted on the influence of selenium on cancer incidence or biomarkers, and except for one, all have shown a positive benefit of selenium on cancer reduction or biomarkers of this disorder. This is consistent with about 100 small animal studies where selenium has been shown to reduce the incidence of tumors in most of these trials. Even though Se MCYS was shown to be the most effective seleno -compound in the reduction of mammary tumors, it may not be the most effective seleno -compound for reduction of colon tumors as reported by Oregon State University researchers.

7. Jay Christian, W., et al., "Distribution of urinary selenium and arsenic among pregnant women exposed to arsenic in drinking water", Environmental Research, Volume 100(1), January 2006.

Inorganic arsenic is a well-known toxicant and carcinogen and found naturally in surface and groundwater around the world. Exposure can cause skin lesions, adverse reproductive outcomes, and cancer. There are two main pathways of arsenic metabolism in humans: the reduction reactions and the oxidative methylation reactions.  Data collected in Chile from 93 pregnant women evaluated the metabolic association between selenium and arsenic compounds. Urinary selenium levels were found to be correlated with urinary arsenic levels in bivariate analysis. Multiple linear regression analyses revealed that higher urinary selenium levels were associated with increased urinary arsenic excretion, increased percent of dimethylarsenate, and decreased percentage of inorganic arsenic. The results of this study suggest that in populations exposed to arsenic, selenium intake may be correlated with urinary arsenic excretion, and may alter arsenic methylation.

8. Cooper, L.T., et al., "The roles of selenium and mercury in the pathogenesis of viral cardiomyopathy", Congestive Heart Failure, Volume 13(4), July 2007.

Discovery of interactions of trace elements with causes for nonischemic dilated cardiomyopathy (DCM) has heightened awareness of potential contributions of environmental variables to DCM pathogenesis. Based on recent studies at the Mayo Clinic, the authors propose a novel paradigm for the pathogenesis of viral DCM that incorporates trace element (mercury and selenium ) imbalance and its interactions with the cellular physiology of viral-induced cardiomyocyte dysfunction.

9. Henshel, D., et al., "New bioindicators for mercury toxicological assessment: Recommendations from the first international bioindicators roundtable", Environmental Bioindicators, Volume 2(3), July 2007.

The Mercury Roundtable at the second meeting of the new International Society of Environmental Bioindicators gathered human health, wildlife, and molecularly focused researchers to evaluate the current status of mercury bioindicators. The most commonly used indicator of mercury exposure in both humans and wildlife is mercury tissue concentrations. Few bioindicators have been validated for use in both human and wildlife populations, but endpoints that focus on brain development and reproductive function are used in both humans and wildlife. Endpoints that may be most publicly and politically persuasive include impotence, autism, and cerebral palsy with mental retardation. Recommendations include the evaluation of additional co-contaminated residues in tissues, such as selenium , as the toxicity is related to the Hg: Se ratio.

10. Brunnell, J.E., et al., "Medical Geology: A Globally Emerging Discipline", Geologica Acta, Volume 5(3), 2007.

Medical Geology, the study of the impacts of geological materials and processes on animal and human health, is a dynamic emerging discipline bringing together the geosciences, biomedical, and public health communities to solve a wide range of environmental health problems. The review examines both deficiency and toxicity of trace element exposure. Goiter is discussed, as is deficiency of selenium in the soil as the cause of juvenile cardiomyopathy and muscular abnormalities. High concentrations of arsenic in the groundwater but also coal combustion of mineralized coal with high arsenic concentrations in Asia, Africa, Europe, North and South America are causing arsenic poisoning. Dental and skeletal fluorosis also impacts the health of millions of people around the world and like arsenic, is due to naturally high concentrations in water and to a lesser extent, coal combustion. Other medical geology issues described include geophagia, exposure to radon, and ingestion of high concentrations of organic compounds in drinking water.

 

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