Scottish Trace Element and Micronutrient Reference Laboratory

Scotland's specialised laboratory for trace elements and vitamins in health and disease

Selenium (Se)

Trace Elements

Vitamins

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This element has attracted great interest as an essential element, particularly as certain diseases have been eradicated by supplementation with selenium. Current interest is the prevention of certain cancers by supplementation with selenium.

The soil in parts of New Zealand, China and Finland are notably selenium deficient and this is reflected in lower selenium concentrations in blood and urine. An unusual form of cardiomyopathy (Keshan Disease) was found to be endemic in an area of China and has now been prevented by prophylactic administration of supplemental selenite.

Patients receiving supplemental nutrition with highly purified synthetic nutrients either orally or during total parenteral nutrition (TPN) can become selenium depleted. Only rarely does this cause overt clinical signs and symptoms such as muscle weakness and pain and cardiomyopathy.

Selenocysteine is the biologically active form and is involved in the active site of several enzymes involved in oxidation-reduction reactions. There is persuasive evidence suggesting that selenium above normal UK reference intervals helps protect against oxidant stress, improves immuno-responsiveness. and lowers overall risk of cancer.

Selenium status can be assessed by measurement of plasma selenium which responds to changes in intake. It is however subject to an acute phase response which lowers the concentration by up to 60% immediately following a trauma. Measurement of a selenoprotein, glutathione peroxidase, provides a further additional test for selenium status. It responds more slowly than selenium to changes in intake and is not subject to an acute phase response. We have found that measurement of whole blood glutathione peroxidase gives results which are comparable to those obtained on red cells when the results are expressed as a ratio to haemoglobin and so we have now adopted whole blood measurement as the sample preparation is simpler.

The difference between dietary requirement and a toxic intake of Se is only a factor of 10 fold, this is lower than for any other essential element. Toxic reactions are reported at intakes of 1500 µg/day. Seleniferous areas exist where soil levels are high and toxic effects on farm livestock is a problem. In man Se toxicity presents as skin eruptions, gastrointestinal upset, hair and nail changes, and discoloration of teeth. An increased incidence of dental caries is also reported.

Sample Requirements and Reference Values

Selenium

Blood Glutathione Peroxidase

Alan Kelly and Ewan Macdonald discussing quality control in the analysis of a batch of samples by graphite furnace atomic absorption spectrometry

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