Selenium

Selenium first attracted attention back in the 1930's as a toxic trace element that caused hair loss and blind staggers in livestock consuming plants that had high concentrations of selenium in South Dakota. However in modern times selenium has now been recognised for over 40 years to be an essential mineral in human nutrition that assists in optimising health and maintaining general wellbeing.

Selenium occurs in all human organs at very low concentrations however higher concentrations of selenium are found in the liver, kidneys and pancreas. In men, there are also higher concentrations of selenium found within the testes and seminal vesicles.

Selenium plays an important role in one of the most powerful antioxidant systems within the body. It interacts with vitamin E to prevent the free radicals that are produced during normal metabolism from damaging body fat and other tissues. Selenium is also important in a number of cellular functions including cell growth and in the transformation and recycling of vitamin C, another powerful antioxidant. A studied published in the Lancet also suggests that selenium has been shown to have mood-enhancing properties.

The potential role of selenium in cancer prevention is well established however few intervention studies have been done to date. One of the most significant studies which included 34,000 men showed that high selenium intakes had a protective affect against prostate cancer. There is also growing evidence that selenium may reduce the risk of lung, stomach, oesophageal and colorectal cancers, however it's not all good news as there are also some studies that suggest that selenium may have a negative effect on skin cancer. Although further studies need to be conducted before any real conclusions can be made, at this stage supplement mixtures containing selenium along with other antioxidants such as vitamin E, vitamin C and beta-carotene appear to be most protective.

Selenium deficiencies are rare, however may be more common in areas where soils have been overworked, or in areas where the soil concentration levels are generally low for example New Zealand, Finland and some areas of China.

Although there is limited data, selenium toxicity can occur and is most common among those who supplement with high doses. Symptoms include nausea, diarrhoea, fatigue, skin and nerve damage, and loss of hair and nails.

Foods that are high in selenium include brazil nuts, seafood, some meats and fish, wholegrain products, oats and brown rice. Most of our selenium demands are met through plants foods in our diet however the selenium content of plant foods will vary depending on the content of selenium in the soil.

References:
1. Mann, J., Truswell, S. Essentials of Human Nutrition. Oxford Medical Publications, New York. 2000.
2. Hass, E. Staying Healthy with Nutrition. Celestial Arts, Berkley CA, 1992.
3. Stanton R. Foods that harm, foods that heal: An A-Z guide to safe and healthy eating. Readers Digest; 2006, pp 256-261.
4. National Health and Medical Research Council. Nutrient Reference Values for Australia and New Zealand. Department of Health and Ageing; 2006, pp 221-227.
5. Rayman MP. Lancet 2000; 356:233-241.
6. Yoshizawa K, Willett WC, Morris SJ, Stampfer MJ, Spiegelman D, Rimm EB, Giovannucci E. Study of prediagnostic selenium levels in toenails and the risk of advanced prostate cancer. J Natl Cancer Inst 1998; 90:1219–1224.

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