This article examines the case for selenium as a cancer preventive agent. The evidence is now overwhelming that dietary selenium is an essential mineral important for health. Selenium deficiency is a known cancer risk, and supplementation is beneficial for those with selenium deficiency.

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Selenium Toxicity Diagnosed

by Dr. House

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Selenium Toxicity from overconsumption of Brazil Nuts, called selenosis, was "reported" on an episode of Dr. House, a medical TV show that often takes artistic liberties to enhance entertainment value. In reality, there has never been a reported case of Selenosis from ingesting Brazil nuts. This is merely one example of many egregious errors and biases against natural medicine on the Dr. House series. This is to be expected, considering the massive drug company advertising supporting the show. This article will examine the case for selenium as a cancer preventive.

Above Left Image: Dr Gregory House Courtesy of Wikimedia

Evidence that Selenium Prevents Prostate Cancer

Selenium Prevents Prostate Cancer in Genetic Mice

An elegant study from the University of Illinois in the 2006 Proceedings of the Nat Academy of Science used mice that were genetically manipulated to have both a selenoprotein deficiency, and an increased prostate cancer incidence. The selenoprotein-deficient mice exhibited accelerated development of prostate cancer in the form of prostate intra-epithelial neoplasia with microinvasion. This study clearly implicated selenoprotein deficiency as a risk factor for prostate cancer, and selenium as a preventive agent.(2)

Yet another transgenic mouse prostate cancer study published in May 2009 AACR by Wang et al showed inhibition of prostate cancer and increased survival in mice treated with selenium compounds.(3)

Left Image: L-selenocysteine, the most biologically active selenium dietary supplement, courtesy of wikimedia commons

Selenium Prevents Colon Cancer in Genetic Mice

Irons et al published a study in the 2006 Journal of Nutrition by evaluating colon cancer in genetically altered mice, deficient in selenoproteins. The mice were given dietary selenium, and the colon was studied for cancer formation. The mice supplemented with dietary selenium had reduced colon cancer, with fewer pre-neoplastic lesions of the colon, This was true for both seleno-protein deficient mice as well as normal mice. (4)

A second colon cancer study in mice from India published in the 2009 World Journal of Gasteroenterology showed that dietary selenium supplements reduced colon cancer tumors by 40 % in mice chemically treated with carcinogens to induce colon cancer.

Selenium Levels PredictBreast Cancer Risk

A study published in 1985 in Japan Cancer Research looked at serum selenium levels in American and Japanese women with breast cancer. Healthy Japanese women had higher selenium levels of 286 mcg/ml compared to Japanese women with breast cancer who had lower selenium levels of 195 mcg/dl. For healthy American women, serum selenium was higher at 191 compared to American women with breast cancer who had lower selenium of 167 mcg/ml. (6)

Above Left Image: Brazil Nuts Are High in Selenium Courtesy of Wikimedia Commons

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

The BRCA gene is a mutation associated with increased risk of breast and ovarian cancer. Women with the BRCA1 gene mutation face an 80% lifetime risk of breast cancer and 40% lifetime risk of ovarian cancer. The BRCA1 gene manufactures proteins involved in repairing oxidative damage to DNA, with repair of the double-stranded DNA breaks. The BRCA gene test is available from Myriad Genetics, which holds a patent on the human gene sequence.

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

A report of selenium toxicity in the US appeared in the 2010 Archives of Internal Medicine. Two Hundred cases of selenosis were caused by an error in manufacturing a liquid dietary supplement, which was subsequently recalled by the FDA.(13)(14) The recalled dietary supplement contained 200 times the labeled concentration of selenium, providing 40,000 mcg per day. For the 200 cases identified, the average serum selenium level was 751 mcg/ML. Symptoms of selenium toxicity include diarrhea, fatigue,hair loss, joint pain, nail discoloration or brittleness, and nausea. In view of this report, it would appear prudent to avoid liquid selenium preparations, and stick with tablets from known reputable sources. In addition, it is recommended that you work closely with a knowledgable physician who can measure serum selenium levels prior to, and during supplementation.

Nutritional Prevention of Cancer Trial (NPC Trial)-1996

The NPC Trial, published in 1996 in JAMA, was the brainchild of Larry C Clark and Gerald Combs, and the first prospective double-blind, placebo-controlled, randomized trial in the Western world to test a selenium supplement on a large population and measure cancer incidence. Clark chose selenized yeast containing 200 mcg of elemental selenium for residents of the southeastern United States, where soil selenium levels are the lowest in the nation. Between 1983 and 1991, seven dermatology clinics recruited a total of 1,312 patients, with a mean age of 63 years, who had a history of basal and/or squamous cell carcinoma. The NPC Trial showed selenium supplementation significantly decreased the total cancer incidence by 50 percent, and specifically dropped the incidence of lung cancer by 48 percent, prostate cancer by 63 percent, and colorectal cancer by 58 percent. Those who entered the trial with plasma selenium levels less than 106 ng/mL showed both the greatest protection from selenium and the highest rates of subsequent cancer in the control group. (26)(27)

The selenized yeast tablet used in the NPC trial was called Seleno-Excell from Cypress Systems which is available at your local vitamin shop or health food store under various brand names. (Note: I have no financial interest in any selenium products mentioned)

The SELECT Study - Selenium and Vitamin E Found Useless at Cancer Prevention

The 1996 NPC trial reigned supreme until it was "discredited" December 2008, by the disappointing results of the 2009 SELECT study, with Time Magazine and The New York Times proclaiming selenium and vitamin E useless for prevention of prostate cancer. (32)(33)

The SELECT study was a randomized, placebo-controlled trial of Selenium and Vitamin E given to 35,533 men 50 years or older, and PSA of 4 ng/mL or less to determine if the vitamins reduced risk of prostate cancer. The vitamins used were: 200 mcg of L-selenomethionine and 400 IU of synthetic vitamin E (all rac--tocopheryl acetate). The results showed the vitamins did not prevent prostate cancer in this group. (29)

SELECT - Why Did It Fail ?

Hatfield and V Gladyshev summarize the reasons why SELECT failed and why the NPC trial and many previous studies succeeded in showing a benefit of selenium supplementation (30). Rayman and Combs also commented on the SELECT study in a JAMA editorial .(31)

The major reason for failure is the SELECT patients started with higher serum selenium levels, in the range above 135 mcg/L found not to benefit from selenium supplementation. They already had plenty. It's not difficult to design a study to fail, simply select the subjects who are not deficient in selenium, and this is repeated over and over in the medical literature.

The subjects enrolled in SELECT had higher initial plasma levels of selenium than those in the NPC trial (135 ng/ml compared to 113 ng/ml, respectively). The subjects in the NPC trial were selected, in part, on the basis of their having relatively low serum selenium levels it was in this cohort that selenium supplementation was effective in reducing cancer risks.

Blood Selenium Levels below 130 ng/ml benefit from supplementation

In agreement with Dr Rayman, a 2008 study published by Bleys in the Archives of Internal Medicine found an inverse correlation between serum selenium and all cause and cancer mortality, with reduced mortality up to a serum selenium level of 130 ng/ml. (34)

A study published by Vogt in the 2003 International Journal of Cancer evaluated selenium levels in 212 men with prostate cancer, compared with healthy controls.They found "a moderately reduced risk of prostate cancer at higher serum selenium concentrations" above 135 ng/ml.(1)

Conclusion, the evidence is overwhelming that dietary selenium is an essential mineral important for health. Selenium deficiency is a known cancer risk, and supplementation beneficial for those with serum selenium levels below 135 mcg/ML. Since selenium is toxic at high doses, it is recommended that you work closely with a knowledgable physician who can monitor levels.

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The reader is advised to discuss the comments on these pages with his/her personal physicians and to only act upon the advice of his/her personal physician. Also note that concerning an answer which appears as an electronically posted question, I am NOT creating a physician -- patient relationship. Although identities will remain confidential as much as possible, as I can not control the media, I can not take responsibility for any breaches of confidentiality that may occur.

Links and References Available at original article.

Financial Disclosure: The author has no financial interest in any selenium supplement manufacturing companies or products.

Authors Website: http://jeffreydachmd.com

Authors Bio:

Jeffrey Dach MD is a physician and author of three books, Natural Medicine 101, and Bioidentical Hormones 101, and Heart Book all available on Amazon, or as a free e-book on his web sites.

Dr. Dach is founder and chief medical officer of TrueMedMD, a clinic in Davie, Florida specializing in Bioidentical Hormones, natural thyroid, functional medicine and low level laser therapy.

Dr. Dach was originally trained and board certified as an Interventional and Diagnostic Radiologist, and worked in the hospital setting for 30 years in Broward County at the Memorial Hospital System. Because of declining visual acuity, Dr Dach retired from radiology and returned to clinical medicine about 8 years ago when he founded the TruMedMD Clinic offering bioidentical hormones and natural thyroid to the South Florida region. For more information about Dr Dach, you can find his entire CV posted on-line on his web site.