The Case for Selenium As Cancer Preventive

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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