Evidence that Selenium Prevents Breast Cancer
A study in Israel published in 1988 evaluated serum selenium levels in 32 breast cancer patents compared to controls. They found significantly lower serum selenium levels in the breast cancer patients (.076 ppm) compared to controls (.119 ppm) (7)
Selenium Prevents Breast Cancer in Mice
In a 1991 publication from Cancer Research, mice with chemically induced breast cancer(DMBA) were treated with dietary selenite. Tumor incidence correlated inversely with the quantity of selenite consumed, clearly demonstrating inhibition of breast cancer by dietary selenium consumption.(8)
Selenium Beneficial for BRCAGene Cariers - Reduces Breast Cancer - The most convincing evidence of selenium as a cancer preventive
Dziaman T et al. from Poland published a study in Nov 2009 looking at DNA damage in BRCA gene carriers. They measured serum and urinary products of DNA oxidation with and without selenium supplementation, finding that damaged DNA products were higher in women with BRCA mutations, and were reduced by selenium supplementation. Their results suggest that BRCA1 deficiency contributes to Oxidative Damage and Breaks in cellular DNA, which may be responsible for cancer development. In addition, selenium supplementation is beneficial, because it protects from oxidative DNA damage.(9)
Strong Evidence for a Selenium as Preventive Agent - Kowalska
A study of BRCA gene carriers from Kowalska in Poland in 2005 provides strong evidence for selenium as a preventive agent. Fifty five women with the BRCA1 gene mutation were supplemented with 275 mcg of sodium selenite, daily for 8 weeks. The amount of DNA damage was assessed from blood lymphocytes showing BRCA gene carriers had twice the DNA damage compared to their normal siblings. However, Selenium supplementation given to BRCA gene carriers reduced the DNA damage to normal levels found in their siblings.(10)
A second larger study reported by Kowalska in 2006 verified that selenium supplementation indeed reduces cancer in women with the BRCA1 gene. After two years of selenium supplementation, expected BRCA1-associated cancers were reduced in half.(11)
Sep 15 Selenoprotein Genome and Breast Cancer
Which seleno-protein is the best candidate for breast cancer protection? One of the new selenoproteins discovered is the Sep15 protein, and the gene for this protein is commonly found to be damaged or lost in breast cancers and other solid tumors (12)
Dietary Sources of Selenium
One of the highest dietary sources of selenium is Brazil Nuts, each providing 12-50 mcg of seleno-methionine. (15) Strunza studied selenium levels in volunteers who ingested 11 Brazil nuts per day for 15 days. Serum selenium rose from 55 mcg/ML to 208 Mcg/mL at the end of the 2 week study. There were no ill effects reported. (16)
A Case of Selenium Toxicity Diagnosed by Dr. House
As mentioned above, Selenium overdose from Brazil nut ingestion (ie Selenosis) was "reported" in an episode of Dr. House. In reality, there has never been a reported case of Selenosis from ingesting Brazil nuts in the US where selenosis is exceedingly rare, and usually due to exposure to an industrial or chemical plant accident, or dietary supplement manufacturing error.(17)-(21)
Left Image: Dr Gregory House Courtesy of Wikimedia Commons.
Toxicity of Selenium Excess
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