Prior to 1990 the selenium status in the New Zealand population, especially in the South Island, was low due to the low selenium content of our soils, but has since improved, while remaining lower than some countries1, 2. However, clinically significant selenium deficiency has not been found in the general population of New Zealand, and is confined to patients with malnutrition or malabsorption1.
Epidemiological studies which demonstrated an association between low serum selenium levels and increased incidence of some cancers and mortality3 as well as an early randomised controlled trial4 suggested that selenium supplements could reduce the incidence of prostate and other cancers. This led to a major randomised controlled trial (SELECT) which has conclusively shown that selenium supplementation does not produce any reduction in prostate cancer or cancer of any type5.
Testing plasma selenium levels is only required in patients with malnutrition or malabsorption, or if selenium poisoning is suspected. People who eat a reasonable diet (including vegetarians) and do not have malabsorption are not at risk for selenium deficiency, do not need selenium supplements, and do not need to have their blood selenium levels tested.
References
1. Thomson CD. Selenium and iodine intakes and status in New Zealand and Australia. Br J Nutr. 2004;91:661-672
2. Thomson CD, Robinson MF. The changing selenium status of New Zealand residents. Eur J Clin Nutr. 1996;50:107-114
3. Bleys J, Navas-Acien A, Guallar E. Serum selenium levels and all-cause, cancer, and cardiovascular mortality among US adults. Arch Intern Med. 2008;168:404-410
4. Clark LC, Combs GF, Jr., Turnbull BW et al. Effects of selenium supplementation for cancer prevention in patients with carcinoma of the skin. A randomized controlled trial. Nutritional Prevention of Cancer Study Group. JAMA. 1996;276:1957-1963
5. Lippman SM, Klein EA, Goodman PJ et al. Effect of selenium and vitamin E on risk of prostate cancer and other cancers: the Selenium and Vitamin E Cancer Prevention Trial (SELECT). JAMA. 2009;301:39-51
Compiled by Assoc. Prof. James Davidson, Labplus, Auckland City Hospital