Selenium

From CRSWiki

Selenium is an element with the atomic number 34. Trace amounts of it are necessary for cellular function in most (possibly all) animals. Thus, it is known as a "trace mineral."

Risks associated with excessive supplementation

There's now a lot of evidence (e.g., (1-6)) that even getting much more than the *RDA* of Se gives no additional benefit to some cancers, and may INCREASE the risk of others. The most important evidence (e.g., (1-5)) came from the Nutritional Prevention of Cancer Study -- the big RCT of selenium vs. skin cancer whose initial results were very promising for Se, led to every damned Se supplement out there containing their 200 mcg. dose, and is cited everywhere as definitive proof of Se supplementation's ability to reduce cancer incidence & mortality (initially a reasonable conclusion (though it was not properly emphasized that the population was intentionally chosen to be Se-deficient, thus making the cohort result dubiously extrapolable to the population at large), but its ongoing, unqualified, dogmatic repetition now constitutes borderline-criminally-negligent oversimplification) -- and sometimes even THIS gets misrepresented, as when a supplement company cites multiple reports from this SAME STUDY as if they were SEPARATE trials confirming Se's ability to protect from cancer.

To understand the significance of (1-5) below, you should know that the cutoff separating the bottom from the top 2 tertiles of plasma Se was almost exactly the same level whose acquisition by the population is targeted by the RDA -- i.e., the bottom tertile was very likely composed almost entirely of people who started the trial RDA-deficient in Se, and the top 2, almost entirely of people who weren't. See also:

http://groups.google.ca/group/sci.life-extension/msg/d86fbc7602016068

1: Clark LC, Combs GF Jr, Turnbull BW, Slate EH, Chalker DK, Chow J, Davis LS, Glover RA, Graham GF, Gross EG, Krongrad A, Lesher JL Jr, Park HK, Sanders BB Jr, Smith CL, Taylor JR. Related Articles, Links Abstract 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 Dec 25;276(24):1957-63. Erratum in: JAMA 1997 May 21;277(19):1520. PMID: 8971064 [PubMed - indexed for MEDLINE]

2: Duffield-Lillico AJ, Reid ME, Turnbull BW, Combs GF Jr, Slate EH, Fischbach LA, Marshall JR, Clark LC. Related Articles, Links Free Full Text Baseline characteristics and the effect of selenium supplementation on cancer incidence in a randomized clinical trial: a summary report of the Nutritional Prevention of Cancer Trial. Cancer Epidemiol Biomarkers Prev. 2002 Jul;11(7):630-9. PMID: 12101110 [PubMed - indexed for MEDLINE]

3: Reid ME, Duffield-Lillico AJ, Garland L, Turnbull BW, Clark LC, Marshall JR. Related Articles, Links Free Full Text Selenium supplementation and lung cancer incidence: an update of the nutritional prevention of cancer trial. Cancer Epidemiol Biomarkers Prev. 2002 Nov;11(11):1285-91. PMID: 12433704 [PubMed - indexed for MEDLINE]

4: Duffield-Lillico AJ, Dalkin BL, Reid ME, Turnbull BW, Slate EH, Jacobs ET, Marshall JR, Clark LC; Nutritional Prevention of Cancer Study Group. Related Articles, Links Abstract Selenium supplementation, baseline plasma selenium status and incidence of prostate cancer: an analysis of the complete treatment period of the Nutritional Prevention of Cancer Trial. BJU Int. 2003 May;91(7):608-12. PMID: 12699469 [PubMed - indexed for MEDLINE]

5: Duffield-Lillico AJ, Slate EH, Reid ME, Turnbull BW, Wilkins PA, Combs GF Jr, Park HK, Gross EG, Graham GF, Stratton MS, Marshall JR, Clark LC; Nutritional Prevention of Cancer Study Group. Related Articles, Links Free Full Text Selenium supplementation and secondary prevention of nonmelanoma skin cancer in a randomized trial. J Natl Cancer Inst. 2003 Oct 1;95(19):1477-81. PMID: 14519754 [PubMed - indexed for MEDLINE]

6: Waters DJ, Shen S, Glickman LT, Cooley DM, Bostwick DG, Qian J, Combs GF Jr, Morris JS. Related Articles, Links Free Full Text Prostate cancer risk and DNA damage: translational significance of selenium supplementation in a canine model. Carcinogenesis. 2005 Jul;26(7):1256-62. Epub 2005 Apr 7. PMID: 15817614 [PubMed - indexed for MEDLINE]

Sources

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