According to the National Institutes of Health, selenium is a trace mineral required in small amounts for good health. In the body, selenium is synthesized into antioxidant enzymes, which are important free-radical scavengers. It is selenium's action as a free-radical scavenger that prompted scientific investigation into selenium's potential role in helping to prevent a variety of cancers. The inconclusiveness of the data has discouraged further investigation into selenium's use as a cancer treatment.
Bladder Cancer Risk
Researchers reporting in the August 2010 issue of "Cancer Epidemiology, Biomarkers & Prevention" performed a meta-analysis of seven published studies to determine the relationship between selenium levels and bladder cancer risk. The researchers measured selenium levels in blood serum and toenails. The authors found that high selenium levels did afford a significant protective effect, and the effect was most pronounced in women. The authors concluded that more studies are necessary before recommending high selenium intake for bladder cancer prevention.
Prostate Cancer
PSA, or prostate specific antigen, is a protein manufactured exclusively by the prostate gland, and physicians test for elevated levels of PSA in blood serum as an indicator of prostate cancer. Researchers reporting in the May 2003 issue of "BJU International" analyzed data from the Nutritional Prevention Cancer trial, or NPC, to determine if there is any protective effect against prostate cancer from selenium. The researchers found selenium did significantly reduce the incidence of the cancer, but the protective effect was limited to men with the lowest levels of PSA.
Lung Cancer
The NPC trial data was also used by researchers reporting in the November 2002 issue of "Cancer Epidemiology, Biomarkers & Prevention" to examine the effects of selenium on lung cancer incidence. The researchers noted that in approximately 100 studies performed over three decades two-thirds reported a reduction in cancerous tumor incidence. However, the NPC data analysis produced conflicting results. Selenium supplementation did not decrease lung cancer incidence in the full population, and further, participants with the lowest serum levels of selenium had the lowest lung cancer incidence.
Cochrane Review
Researcher reviewers reporting in the April 2011 issue of "The Cochrane Library" performed a meta-analysis of 55 published studies on selenium and cancer risk. According to the authors, there is no convincing evidence that selenium can reduce cancer risk. In fact, the authors point to data collected from the NPC trial that suggest there may be some harm to supplementation. However, the reviewers cautioned that their findings have limitations due to study design, quality and mixed data sets that complicated their analysis.
References
- Office of Dietary Supplements: Selenium
- "Cancer Epidemiology, Biomarkers & Prevention"; Selenium and Bladder Cancer Risk: A Meta-analysis; Andre Amaral et al.; August 2010
- "BJU International"; Selenium Supplementation, Baseline Plasma Selenium Status and Incidence of Prostate Cancer: An Analysis of the Complete Treatment Period of the Nutritional Prevention of Cancer Trial; Anna Duffield-Lillico et al.; May 2003
- "Cancer Epidemiology Biomarkers & Prevention"; Selenium Supplementation and Lung Cancer Incidence: An Update of the Nutritional Prevention of Cancer Trial; Mary Reid et al.; November 2002
- "The Cochrane Library"; Selenium for Preventing Cancer; Gabriele Dennert et al.; April 2011
