Selenium-rich Foods May Protect Against Bladder Cancer
September 29, 2010
Bladder cancer is one of the most common cancers worldwide, yet many cases are not explained by known risk factors, such as smoking and workplace chemicals. Researchers have thus been looking for other possible contributors, such as diet. Results of a new study, reported in Cancer Epidemiology, Biomarkers & Prevention, suggest that getting enough selenium, in particular, may help keep bladder cancer at bay.
Using data from seven previously published studies, researchers looked at the connection between selenium (a trace mineral) and bladder cancer risk in nearly 20,000 people. Those with the highest selenium levelsas measured in toenails and bloodhad a 39 percent lower risk of developing bladder cancer, with the most protection seen in women. (Toenail selenium levels are actually a good measure of long-term selenium intake, while blood levels indicate more recent intake.) Earlier studies have suggested that selenium may also protect against other types of cancerlung, prostate, and intestinal, for examplethough not all results have been consistent.
Selenium may help fight cancer by acting as an antioxidant, the researchers say. It may also help cancer cells self-destruct and help repair damaged DNA, among other mechanisms. It's unclear, though, why women in the current study were more protected than men.
"In conclusion, this meta-analysis supports an inverse association between selenium concentration and bladder cancer risk," write the study authors. Larger observational and randomized trials are needed to confirm the results.
What to do. Look to foods first for selenium, not supplements. The best sources are whole grains such as brown rice and whole wheat bread (eat several servings a day); seafood (eat two to three servings a week, also for its heart-health benefits); and nuts. Poultry and some red meats are other good sources. Brazil nuts are especially rich in seleniumjust one (5 gram) kernel has 95 micrograms of selenium, which is nearly twice the daily recommended intake for adults (55 micrograms).
Too much selenium can be harmful, however. The difference between an optimal and toxic dose is small. The safe upper limit for adults is 400 micrograms a day. Multivitamin/mineral pills typically provide 20 to 200 micrograms of selenium. If you do take a selenium supplement, don't take more than 200 micrograms a day.
Sources: Amaral AF et al. Selenium and Bladder Cancer Risk: a Meta-analysis. Cancer Epidemiol Biomarkers Prev. 2010 Sep;19(9):2407-15. and "Dietary Supplement Fact Sheet: Selenium" by the Office of Dietary Supplements of the National Institutes of Health.