A large-scale meta-analysis of studies linking selenium supplementation with the risk of bladder cancer and other cancers finds that there is not enough evidence to recommend the nutritional supplement for cancer patients.
The Italian researchers describe selenium as “a metalloid with both nutritional and toxicological properties”. While some studies have suggested that higher selenium levels and/or selenium supplementation may have a protective effect against malignancies like bladder cancer, the newest Cochrane Database of Systematic Reviews report says the data supporting such a link is incomplete, at best.
The group included prospective observational studies of selenium supplementation in patients with bladder cancer and other cancers, as well as randomized controlled trials comparing the effect of selenium in both cancer patients and healthy adults. Studies were pulled from the Cochrane Central Register of Controlled Trials as well as the databases MEDLINE, EMBASE, CCMed and CancerLit dating back as early as 1966.
Although the group did find some evidence of a link between selenium and bladder cancer, a cancer more common among diabetics and those who have taken Actos, they concluded that the studies were unconvincing.
“The most pronounced decreases in risk of site-specific cancers [with selenium] were seen for stomach, bladder, and prostate cancers,” reports the study’s lead author, Marco Vinceti of the University of Modena and Reggio Emilia in Modena, Italy. “However, these findings have limitations due to study design, quality and heterogeneity that complicate interpretation of the summary statistics.”
The report, which is an update of a 2011 Cochrane Database report on selenium and cancer, stops short of saying that the supplement has no value in the treatment or prevention of malignancies like bladder cancer. The authors concede that certain underlying genetic factors may make some cancer patients more likely to benefit from selenium supplements and say the idea deserves further study. But, based on existing research, Dr. Vinceti and his colleagues conclude, “To date, no convincing evidence suggests that selenium supplements can prevent cancer in humans.”
Bladder cancer impacts more than 70,000 people in the US each year, many of them diabetics who have been prescribed the insulin sensitizer Actos. Last June, India recently became the most recent country to join the list of countries that have suspended the use of Actos for diabetes because of its potential link to bladder cancer. While the US has not banned Actos for diabetes, the FDA has required the company to include a bladder cancer risk warning on its packaging since 2011.
Vinceti, M et al, “Selenium for Preventing Cancer, Cochrane Database of Systematic Reviews, March 2014, Epub ahead of print
Sadikot, SM and Ghosal, S, “India suspends pioglitazone: Is it justified?”, Jan-march, 2014, Diabetes and Metabolic Syndrome, pp. 53-56