Selenium may worsen prostate cancer in some men

MedWire News: High levels of selenium in the blood may worsen prostate cancer in some men who already have the disease, results of a US study suggest.

In recent years, selenium supplements have been promoted as a means of preventing prostate cancer, largely based on observational studies that found higher prostate cancer incidence and mortality in geographical areas that are naturally low in selenium, compared with in those that are naturally high in the mineral.

However, the current research findings suggest that “if you already have prostate cancer, it may be a bad thing to take selenium,” said study researcher Dr Philip Kantoff, from the Dana-Farber Cancer Institute in Boston, Massachusetts, USA.

The team studied DNA and blood samples collected from 489 men, aged an average of 62 years, who were diagnosed with localised or locally advanced prostate cancer between 1994 and 2001.

Around half the men had low-risk disease, one-third had intermediate-risk disease and one-sixth had high-risk disease.

Analysis revealed that, overall, higher levels of selenium in the blood were associated with a slightly increased risk of aggressive prostate cancer.

However, further analysis showed that the risk of aggressive prostate cancer associated with blood levels of selenium was significantly affected by common forms of the SOD2 gene.

For example, men with the highest selenium levels and the ‘AA’ form of the SOD2 gene were 40% less likely to have aggressive prostate cancer than the men with same gene variant but low levels of selenium.

But for men carrying the ‘V’ form of the gene, selenium had the opposite effect. In this group, men with the highest levels of selenium in their blood were about twice as likely to have aggressive prostate cancer as their counterparts with low selenium levels.

Lead researcher Dr June Chan, from the University of California in San Francisco, and team conclude: “These data suggest that the relationship between circulating selenium levels at diagnosis and prognostic risk of prostate cancer is modified by SOD2 genotype and indicate caution against broad use of selenium supplementation for men with prostate cancer.”

The research is published in the Journal of Clinical Oncology.