In a meta-analysis reported in the September, 2010 issue of Cancer Epidemiology, Biomarkers & Prevention, researchers from the Spanish National Cancer Research Center and the U.S. National Cancer Institute conclude that the mineral selenium may have a protective effect against bladder cancer, one of the most common types of cancer worldwide.
Núria Malats, MD, PhD and colleagues analyzed data from 7 epidemiologic studies that reported the association between bladder cancer incidence and selenium levels measured in blood, serum, nails, hair or saliva. The studies included a total of 1,910 bladder cancer patients and 17,339 controls or cohort members who did not have the disease.
The researchers found a 39 percent lower risk of bladder cancer in those with high versus low selenium levels. The protective effect extended mainly to women, who are at lower risk of developing the disease than men.
"Selenium may exert anticarcinogenic effects mainly through selenoproteins, although the specific mechanisms are not yet fully known," the authors write. "Aberrant expression patterns of glutathione peroxidases and selenoprotein P, found in colorectal cancer, show that the antioxidant properties of selenoenzymes are relevant in carcinogenesis and tumor progression, particularly by scavenging reactive oxygen species and diminishing further oxidative damage."
They add that selenium also affects apoptosis (programmed cell death), DNA repair, and carcinogen metabolism.
"The lower the levels of selenium, the higher the risk of developing bladder cancer," observed Dr Malats, who is the leader of the Genetic and Molecular Epidemiology Group at the Spanish National Cancer Research Center's Human Cancer Genetics Program. "Although our results suggest a beneficial effect of high selenium intake for bladder cancer risk, more studies are needed to confirm these findings before an enforcement of high selenium intake is recommended."
"These findings provide a valuable lead for what to do next to understand if there is a role for selenium supplementation in bladder cancer prevention," Cancer Epidemiology, Biomarkers & Prevention Editorial Board Member Elizabeth A. Platz, ScD, MPH concurred.