CAM ConferenceSelenium Linked to Lower Bladder Cancer Risk
By Crystal Phend, Senior Staff Writer, MedPage Today
September 01, 2010
MedPage Today Action Points (this brings the summary to the patient level for better understanding)
Explain to interested patients that a meta-analysis found that higher levels of selenium in toenail and serum samples was associated with a decreased risk of bladder cancer.
Note that the paper was based on a meta-analysis of seven epidemiological studies and that the significant finding was in women and not men.
The trace mineral selenium may help prevent bladder cancer, especially in women, according to a meta-analysis.
Bladder cancer risk overall fell with higher levels of selenium for a pooled odds ratio of 0.61 (95% confidence interval 0.42 to 0.87) for the highest versus lowest selenium levels, found N¨²ria Malats, MD, PhD, of the Spanish National Cancer Research Center in Madrid, Spain, and colleagues.
Women appeared to show a stronger protective effect than men, the researchers reported in the September issue of Cancer Epidemiology, Biomarkers & Prevention.
But physicians should hold off on suggesting selenium supplementation to patients until large observational studies or randomized trials can confirm a benefit, Malats’ group cautioned.
Indeed, further work on the dose-response relationship is needed even in setting recommended daily intakes for the mineral, according to comments attributed to Elizabeth A. Platz, ScD, MPH, of the Johns Hopkins School of Public Health, in a press release.
But Platz, a member of the editorial board of the journal, agreed with the researchers that the meta-analysis findings provide a valuable early step toward determining a possible role in bladder cancer prevention.
Dietary selenium predominantly comes from bread and meats, particularly when they come from areas where soil has higher selenium levels.
Selenium forms compounds with dozens of proteins in the body, together making enzymes that act as antioxidants, although the researchers noted that the specific anticarcinogenic mechanisms are not yet fully known.
The meta-analysis included seven epidemiologic studies published prior to March 2010 for a total of 1,910 bladder cancer cases and 17,339 controls.
Among the studies, three used a case-control design, three a nested case-control design, and one a case-cohort design. The patient populations were predominantly in the United States (four studies) as well as Northern Europe (three studies).
Selenium status appeared inversely linked to bladder cancer risk in each of the studies, although it was not significant in all of them.
The definition of selenium “exposed” individuals considered to have elevated selenium levels varied from over 0.630 ¦Ìg/g to more than 0.95 ¦Ìg/g in toenail samples as a measure of longer-term exposure, and from at least 96.00 ¦Ìg/L to at least 133.1 ¦Ìg/L in serum, which led to some overlap with the control groups between studies.
Stratifying the results by gender showed a significantly decreased risk of bladder cancer with elevated selenium intake in women (odds ratio 0.55, 95% CI 0.32 to 0.95).
For men, the effect was virtually nil. Elevated selenium levels yielded an odds ratio of only 0.95 for bladder cancer risk, which was not significant (95% CI 0.69 to 1.27).
The divergence in selenium’s effect “may result from gender-specific differences in its accumulation and excretion,” Malats’ group suggested in the paper.
Another source of heterogeneity in the meta-analysis was how selenium was measured — from toenail samples in four studies and from serum in the other three.
Both sample sources led to significant inverse correlations between selenium levels and bladder cancer risk, but serum levels were more strongly linked to a protective effect with an odds ratio of 0.33 (95% CI 0.21 to 0.51).
Smoking status — a known risk factor for bladder cancer — also appeared to contribute to heterogeneity in the meta-analysis.
The researchers cautioned about the small number of studies included in the meta-analysis and the heterogeneity seen among them.
The study was supported by the Red Tem¨¢tica de Investigaci¨®n Cooperativa en C¨¢ncer, Instituto de Salud Carlos III, Spanish Ministry of Science and Innovation, and by the Association for International Cancer Research.
The researchers reported having no potential conflicts of interest to disclose.
Primary source: Cancer Epidemiology, Biomarkers & Prevention
Amaral AFS, et al
“Selenium and bladder cancer risk: A beta-analysis”
Cancer Epidemiol Biomarkers Prev 2010;