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ANTIOXIDANTS

Our body naturally produces Free Radicals which can cause severe damage (oxidation) to our cells. Free Radicals become more prevalent with increased levels of stress, and as a result of environmental factors such the presence of certain drugs, pollutants and smoking, and even as a result of vigorous and sustained exercise.

Free radicals are reactive chemicals in the body that destroy cells and tissue. If free radical production becomes excessive, we suffer damaging Oxidative Stress. Free radical damage accumulates with age, indicating a fundamental requirement for us all to minimise the onset and duration of oxidative stress throughout our entire lifetime.

Antioxidants are the body’s natural tools for protecting ourselves against damaging oxidative stress. Antioxidants act as neutralising agents by reacting with free radicals to prevent further damaging activity. Without antioxidants, free radicals continue in a cascade of damaging activity throughout our entire body system. The more free radicals that are produced, the more antioxidants we need.

Fortunately many substances in various foods act as antioxidants. Therefore, we all must eat enough of the right foods in order to promote effective antioxidant activity within our body, and thereby prevent or minimise oxidative stress and subsequent damage to our cells and tissues.

Selenium is an essential component in the selenoenzyme “glutathione peroxidase” which reduces harmful hydroperoxides, and scavenges the free radicals that cause continual damage to cells and hasten ageing effects and onset of degenerative disease.  The amount of glutathione peroxidase within our bodies is an indicator of our level of Selenium.

THE ANTIOXIDATIVE ROLES OF SELENIUM

Selenium (Se) is generally best known for its antioxidant activity.  Oxidative damage to tissues caused by free radicals (including the superoxide radical) has been implicated in the aetiology of a number of major diseases.  While oxygen is fundamental to the processes of human life, responsible in particular for the release of energy from fuel supplied by the diet, under certain conditions, particularly in the form of its reactive oxygen species, it can cause damage, resulting in mutagenesis, carcinogenesis, circulatory disturbances and ageing (Reilly, 1996).  Se plays important roles in the body’s protective mechanisms that prevent oxygen from showing its sinister side.

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The antioxidant nature of Se is different from that of other antioxidant nutrients.  Se functions as a component of antioxidant enzymes, for example, the glutathione peroxidases and thioredoxin reductases, while vitamins E and C react nonenzymatically with oxidant molecules.  Selenoenzymes contain Se in the form of selenocysteine, the 21^st amino acid.  Glutathione peroxidase (of which at least five forms exist) has an antioxidant role in reducing damaging hydrogen peroxide and lipid/phospholipid hydroperoxides produced in eicosanoid synthesis by the lipoxygenase and cyclo-oxygenase pathways (Spallholz et al, 1990).  This function reduces damage to lipids, lipo-proteins and DNA, and hence reduces risk of cardiovascular disease and cancer (Diplock, 1994; Neve, 1996).  Moreover, selenium inhibits tumour necrosis factor-alpha-induced expression of adhesion molecules that promote inflammation (Zhang et al, 2002).

Another group of selenoenzymes, the thioredoxin reductases, are involved in the reduction of nucleotides in DNA synthesis, the regeneration of antioxidant systems, and the maintenance of cellular redox state (Allan et al, 1999).  Selenoprotein P is an abundant extracellular selenoprotein that is rich in selenocysteine. It is usually the most abundant Se form in plasma.  Apart from its Se transport function, rat studies indicate that it also has strong antioxidant properties that protect against liver injury (Burk et al, 2003).

Oxidative stress and inflammation (which involves oxidative stress) are early risk factors for cancer.  A Serbian study found that wheat biofortified with Se reduces oxidative stress in humans.  See the Figure below (Djujic et al, 2000).

In addition to Se’s anti-cancer effects, it is evident that antioxidant selenoenzymes are also involved in reducing the risk of heart disease.  In a study of around 640 patients with suspected coronary artery disease in Germany, a low level of activity of red-cell glutathione peroxidase 1 was independently associated with an increased risk of cardiovascular events.  The authors concluded that “increasing glutathione peroxidase 1 activity might lower the risk of cardiovascular events.” (Blankenberg et al, 2003). [link to Se & the Heart page]

Cigarette smoke provides a rich source of endogenous free radicals.  Indeed, it has been estimated that a single puff of cigarette smoke contains 10¹⁴ free radicals in the gas phase and 10¹⁵ in the tar phase (Reilly, 1996).  These are numbers too large to imagine.  Smokers are under a high and sustained free radical load which is likely to cause tissue damage from the DNA level up.  Recent studies have shown that Se has its strongest antioxidative and anti-cancer effects in male smokers [link to anti-cancer page].  Concurrent Se and vitamin E deficiencies are especially harmful for animals and humans (Schwarz & Foltz, 1957), and this is likely to be of particular importance to male smokers.

Definitions

Free radical: an atom or group of atoms containing at least one unpaired electron and existing for a brief period of time before reacting to produce a stable molecule.

Mutagenesis: the process of induction of genetic mutation (gene alteration), which is generally detrimental to the organism.

Carcinogenesis: the process of induction of cancer, generally via mutagenesis, gene deletions or other DNA disturbances.  Cancer results from repeated division of a single mutant cell whose growth has become unregulated.

Redox: abbreviation of oxidation-reduction.  A reversible chemical process, usually involving the transfer of electrons, in which one reaction is an oxidation and the reverse reaction is a reduction.

Nucleotides: the building blocks of the nucleic acids, DNA and RNA, which are formed from long chains of nucleotides.  Nucleotides are formed from nucleosides (compounds comprising a purine or pyrimidine base linked to a sugar) linked to phosphoric acid.

References

Allan CB, Lacourciere GM, Stadtman TC 1999. Responsiveness of selenoproteins to dietary selenium. Ann Rev Nutr 19: 1-16.

Blankenberg S, Rupprecht HJ, Bickel C, Torzewski M, Hafner G, Tiret L, Smieja M, Cambien F, Meyer J, Lackner KJ 2003. Glutathione peroxidase 1 activity and cardiovascular events in patients with coronary artery disease. N Engl J Med 349: 1605-1613.

Burk RF, Hill KE, Motloey AK 2003. Selenoprotein metabolism and function: evidence for more than one function for selenoprotein P. J Nutr 133: 1517S-1520S.

Diplock A 1994. Antioxidants and disease prevention. Mol Aspects Med 15: 293-376.

Djujic IS, Jozanov-Stankov ON, Milovac M, Jankovic V, Djermanovic V 2000. Bioavailability and possible benefits of wheat intake naturally enriched with selenium and its products. Biol Trace Elem Res 77(3): 273-285.

Neve J 1996. Selenium as a risk factor for cardiovascular diseases. J Cardiovasc Risk 3: 42-47.

Reilly C 1996. Selenium in Food and Health. London: Blackie.

Schwarz K, Foltz CM 1957. Selenium as an integral part of factor 3 against dietary necrotic liver degeneration. J Am Chem Soc 79: 3292-3293.

Spallholz JE, Boylan LM, Larsen HS 1990. Advances in understanding selenium’s role in the immune system. Ann N Y Acad Sci 587: 123-139.

Zhang F, Yu W, Hargrove JL, Greenspan P, Dean RG, Taylor EW, Hartle DK 2002. Inhibition of TNF-alpha induced ICAM-1, VCAM-1 and E-selectin expression by selenium. Atherosclerosis 161(2): 381-386.

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Laucke Flour Mills Pty Ltd
Strathalbyn, South Australia
Bridgewater on Loddon, Victoria
2 Callington Rd Strathalbyn SA 5255
PO Box 200 Strathalbyn SA 5255
E-mail: bread@laucke.com.au
Phone: (08) 8536 5555
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