This review covers current knowledge of selenium in the environment, dietary intakes, metabolism and status, functions in the body, thyroid hormone metabolism, antioxidant defense systems and oxidative metabolism, and the immune system. Selenium toxicity and links between deficiency and Keshan disease and Kashin-Beck disease are described. The relationships between selenium intake/status and various health outcomes, in particular gastrointestinal and prostate cancer, cardiovascular disease, diabetes, and male fertility, are reviewed, and recent developments in genetics of selenoproteins are outlined. The rationale behind current dietary reference intakes of selenium is explained, and examples of differences between countries and/or expert bodies are given. Throughout the review, gaps in knowledge and research requirements are identified. More research is needed to improve our understanding of selenium metabolism and requirements for optimal health. Functions of the majority of the selenoproteins await characterization, the mechanism of absorption has yet to be identified, measures of status need to be developed, and effects of genotype on metabolism require further investigation. The relationships between selenium intake/status and health, or risk of disease, are complex but require elucidation to inform clinical practice, to refine dietary recommendations, and to develop effective public health policies.

Selenium in human health and disease.

Food systems need to produce enough of the essential trace element Se to provide regular adult intakes of at least 40 microg/d to support the maximal expression of the Se enzymes, and perhaps as much as 300 microg/d to reduce risks of cancer. Deprivation of Se is associated with impairments in antioxidant protection, redox regulation and energy production as consequences of suboptimal expression of one or more of the Se-containing enzymes. These impairments may not cause deficiency signs in the classical sense, but instead contribute to health problems caused by physiological and environmental oxidative stresses and infections. At the same time, supranutritional intakes of Se, i.e. intakes greater than those required for selenocysteine enzyme expression, appear to reduce cancer risk. The lower, nutritional, level is greater than the typical intakes of many people in several parts of the world, and few populations have intakes approaching the latter, supranutritional, level. Accordingly, low Se status is likely to contribute to morbidity and mortality due to infectious as well as chronic diseases, and increasing Se intakes in all parts of the world can be expected to reduce cancer rates.

/pdf/selenium-in-global-food-systems-23a5koo10v.pdf

Selenium in global food systems.

Publisher Summary This chapter reviews the geomedical aspects of selenium (Se), ranging from the soil through the plants to animal and human nutrition. Selenium has several essential functions in the animal and human body, and interactions occur with other elements and compounds. The beneficial effects of Se are obtained at different concentration levels, depending on the functions of Se and on interacting factors such as vitamin E, fatty acids, and sulfur. The nutritional minimum level for animals and humans is about 0.05–0.10 ppm Se in dry fodder/food, and intake below that cause severe deficiency diseases. At somewhat higher levels of Se intake, there are indications of a protective effect toward a number of human diseases, and toxic effects of Se occur with exposure to levels of 2–5 ppm Se or more, depending on the chemical form of the Se. Selenium toxicity in livestock is known in a few areas around the world, but Se deficiency has turned out to be much more common than Se toxicity. The Se deficiency problem is severe in New Zealand, in parts of China, in parts of North America, and in the Scandinavian countries.

Selenium in Soils and Plants and its Importance in Livestock and Human Nutrition

Content and bioavailability of trace elements in vegetarian diets.

Selenium dependent glutathione peroxidase activity in human follicular fluid

The selenium state of 40 elderly Belgian people, residing in geriatric homes, has been evaluated. Data are presented on the selenium (Se) contents of their blood, plasma, and erythrocytes. The activity of glutathione peroxidase (GSH-Px) has been assayed. All data were compared with those obtained for 164 young, working adults as presented in Part I of this study. Plasma selenium levels were significantly lower in the old (73 ng/mL) as compared to the young people (97 ng/mL), but erythrocyte Se levels (200 ng/mL) and GSH-Px activity were significantly higher. The selenium concentration in plasma during infancy has also been estimated. The results reveal a very low Se level during the first months of life, with a gradual increase with age. The results are discussed in the light of literature data.

The selenium status of Belgian population groups : II. Newborns, children, and the aged.

A moderate level of selenium (Se) was demonstrated in the blood (123 ng/mL), erythrocytes (RBC) (161 ng/mL), and plasma (97 ng/mL) of 110 male and 54 healthy female Belgian adults by using hydride-generation atomic absorption spectrometry. These values agree well with those found in neighboring countries. The study is the first one to report on normal values for these parameters in Belgians.Glutathione peroxidase (GSH-Px) activity has also been assayed. The group in considered nondeficient. Neither the concentration of Se in blood, plasma, or RBC, nor the activity of GSH-Px in the latter, were related to age, sex, blood pressure, or smoking habits. Oral contraception was associated with elevated plasma Se levels as compared to controls (P<0.01).A statistically significant positive relationship existed between the Se concentrations in whole blood or in red blood cells and red blood cell GSH-Px activity (r=0.31,p<0.005).

M. Verlinden

Papers

The selenium status of Belgian population groups : II. Newborns, children, and the aged.

The selenium status of Belgian population groups : I. Healthy adults.