Selenium is one of those supplements that were are told is good for us and then we are told it is bad for us. Every six months to a year the story and the recommendations seem to change.

According to a study by researchers at Dana-Farber Cancer Institute the University of California, San Francisco higher levels selenium in the blood may worsen prostate cancer in some men who already have the disease, that is today’s latest!

The study results said that a higher risk of more-aggressive prostate cancer was seen in men with a certain genetic variant which is found in about 75 percent of the prostate cancer survivors. Men with this particular genetic variant who also had a high level of selenium in their blood faced a two-fold greater risk of a poorer outcome from their prostate cancer than men with the lowest amounts of selenium. By contrast, the 25 percent of men with a different variant of the same gene and who had high selenium levels were at 40 percent lower risk of aggressive disease. The variants are slightly different forms of a gene that instructs cells to make manganese superoxide dismutase (SOD2), an enzyme that protects the body against harmful oxygen compounds.

The research findings suggest that “if you already have prostate cancer, it may be a bad thing to take selenium,” says Philip Kantoff, MD, director of Dana-Farber’s Lank Center for Genitourinary Oncology and senior author of the study that is published by the Journal of Clinical Oncology on its website now and later will be in a print journal. The lead author is June Chan, ScD, of the University of California, San Francisco.

This study reveals the strong interaction between selenium and SOD2 to influence the biology of prostate cancer. The authors say the current research demonstrated that variations in the make up of the SOD2 gene dramatically alter the effects of selenium on the risk of aggressive prostate cancer.

Selenium is a naturally occurring mineral found widely in rocks and dirt. We believe that small amounts of selenium are essential for good health. Supplemental selenium has been sold and promoted as a means of preventing prostate cancer. These recommendations are largely based on observational studies that found higher risk of prostate cancer incidence and mortality in areas of the country that are naturally low in selenium. Despite this conclusion recent research aimed at confirming the benefits of selenium supplementation have been mixed.

Most recently, the SELECT study, which involved 35,000 men, was halted early when, after more than five years, it showed that the supplements didn’t affect the incidence of prostate cancer.

In this Dana Farber study, researchers examined banked blood samples, DNA, and medical records of 489 male patients diagnosed with localized or locally advanced prostate cancer between 1994 and 2001. Their mean age was 62, and their mean PSA (prostate-specific antigen) measurement was 6.0 ng/mL. About half the men were assessed as having a good disease risk, one-third had an intermediate risk and the remaining one-sixth were at poor risk. The researchers measured the level of selenium in the blood and, using the stored DNA, they determined the SOD2 genotype.

Simply having a high level of selenium was associated with a slightly elevated risk of aggressive prostate cancer. However, the shoe dropper in this study was that the risk was much more strongly affected by the interaction of selenium levels and whether the survivor had a certain variant of the SOD2 gene.

Men with the highest selenium levels and the “AA” form of the SOD2 gene were 40 percent less likely to have been diagnosed with aggressive prostate cancer than the men with same gene form but low levels of selenium. Men carrying the “V” form of the gene, selenium had the opposite effect. In these men, those with the highest levels of selenium in their blood were about twice as likely to have an aggressive type of prostate cancer as was their counterparts with low selenium levels.

“Among the 25 percent of men with the AA genotype, having greater selenium levels may protect against aggressive disease,” the authors concluded. “However, for the 75 percent of men who carry a V allele, higher selenium levels might increase the likelihood of having worse characteristics.”

It is important for you to know to which type of SOD2 gene you have prior to taking selenium supplements. Better yet, do not consider taking a selenium supplement unless there is a very good medical reason.

Since we have been told for years that antioxidants can help people live longer, healthier lives with a lowered risk of cancer these results seem counter intuitive. However, Kantoff says, “There is some precedent to this – research has suggested that antioxidants could be protective if you don’t have cancer, but once you do, then antioxidants may be a bad thing.”

In addition to Kantoff and Chan, other authors of the paper include William Oh, MD, Wanling Xie, PhD, Meredith Regan, ScD, and Miyako Abe, PhD, of Dana-Farber; Meir J. Stampfer DrPH, MD, of Brigham and Women’s Hospital and the Harvard School of Public Health, and Irena King, PhD, of the Fred Hutchinson Cancer Research Center, Seattle.

The work was supported by grants from the National Cancer Institute and several foundations and charitable organizations.

Joel T Nowak MA, MSW