Seleniums Carcinogenic Effects Debated

Seleniums Carcinogenic Effects Debated

RESEARCH TRIANGLE PARK, N.C.--Researchers are bringing up concernsregarding the outcome of a study published in late 2003 in which selenium wasfound to promote the risk of squamous cell carcinoma and total nonmelanoma skincancer (J Natl Cancer Inst, 95, 19:1477-81, 2003) (http://jncicancerspectrum.oupjournals.org).

In the study, data was analyzed from the Nutritional Prevention of CancerTrial, a double blind, placebo-controlled clinical trial designed to testwhether 200 mcg/d of selenium (as selenized yeast) would prevent nonmelanomaskin cancer among 1,312 patients who previously had the disease. The dose wasseen to inhibit prostate cancer but increase squamous cell carcinoma and totalnonmelanoma skin cancer risk.

"I am not sure what is going on with this agent in the skin," thestudys lead author told INSIDER at that time. "Clearly, it doesnot appear to offer protection against skin cancer. Whether it actuallyincreases risk is not as clear. ... Our best estimate is that selenium does notincrease risk by much."

James Huff, Ph.D., from the National Institute of Environmental HealthSciences, wrote in the Feb. 18 Journal of the National Cancer Institute(NCI) (96, 4:333-4, 2004) that the adverse effects of selenium should be takenseriously--especially since selenium sulfide was seen to promote liver and lungtumors in rat models during the 1980s. In addition to causing skin cancers inhumans, these experimental carcinogenic results should caution us that long-termselenium intake may be more hazardous than previously realized, stated Huff,adding researchers should stay on their toes regarding the possible carcinogeniceffects from selenium-containing supplements.

Huff, however, didnt totally dismiss the protective benefits of seleniumin overall incidence of prostate cancer, since this is where the mineral hasshown the most promise. Although, the effect was restricted [in the study] tothose with lower baseline prostate-specific antigen and plasma seleniumconcentrations, he wrote.

Huff concluded that as NCI currently investigates the use of selenium andvitamin E for prostate cancer prevention (the SELECT trial, slated to end in2014), the study volunteers should be closely monitored for signs of other typesof cancer development.

In response to Huff, the October 2003 studys authors reported that it istrue--the toxicity, carcinogenicity and anti-cancer activities of selenium varyfrom compound to compound. "The biologic activity of selenium is very muchdependent on its chemical form," the authors wrote. "Nonetheless, thefact that one selenium compound has deleterious effects does not mean all othersdo."

Industry suppliers noted the study results raise interesting questions."Selenium, although known for having positive benefits in fighting certaincancers--particularly prostate--can have pro-cancer effects when taken in largedoses, especially when taking an inorganic source such as sodium selenite,"said Max Motyka, director of the human products division at Albion AdvancedNutrition in Clearfield, Utah. "Theoretically, any of theantioxidant-involved minerals would be helpful in programs to fight againstcancers, including manganese, copper and zinc, in addition to the aforementionedselenium."

Motyka added that the pro-carcinogenic effects of selenium may be morecomplicated than at first glance. Recently, it was brought to the publicsattention that there was a data grouping that suggested women who had taken avery large number of antibiotics for infections been seen to have a higherincidence of cancer. One thing that we should keep in mind here is that theimmune system, aside from genetics and environmental causes, protects us againstmany things, not just infection. It helps fight off things like cancer. Could itbe that the repeated bouts of infection, which required antibiotic therapy, werepointing out a weakness in the immune system that was the actual precursor tothe cancers involved?"