This meta-analysis suggests that there is an inverse relationship between serum selenium and prostate cancer risk.
Worldwide prostate cancer accounts for 25% of all cancers in men. The most recent tally in 2015 says that one million new cases are added each year. Since 1996, scientists have studies the inverse relationship between geographic soil selenium levels and cancer mortality.
In the decades that followed other studies supported the connection between serum selenium and prostate cancer risk. This recently published meta-analysis on serum selenium and prostate cancer reviewed PubMed, Embase, Medline, and the Cochrane Library literature up until September 2016. After reviewing 1352 studies, the researchers narrowed the field to 17 studies, within which there were 6136 prostate cancer cases and >34,901 controls or participants.
The researchers concluded the following:
“Our study shows that increased serum selenium is associated with a reduced risk of prostate cancer. Selenium is an antioxidant and anticarcinogen.It is also an important component of 3 major proteins: selenoprotein-P, glutathione peroxidase (GPx), and albumin. Within GPx, selenium is part of the most important antioxidant enzyme system that prevents cellular injury.”
“In addition, selenium inhibits the expression of some oncogenes and promotes apoptosis. Selenium is also part of the most important antioxidant enzyme system involved in preventing peroxidation of cells. Like vitamin E, selenium may be a superior scavenger of reactive nitrogen oxide species, and has the capacity to decrease inflammation.9 Selenium also inhibits cell proliferation and decreases cell cycle progression through the reduction of cyclin in prostate cancer cell lines.” See Figure 1.
Why this study is significant:
1. Comprehensive as it included all relevant studies.
2. Large sample size, which enhances the “statistical power,” thus lending reliability of the results.
3. There was a significant inverse relationship between serum selenium levels and prostate cancer risk.
4. Since serum selenium is a broad indicator of selenium in the diet, the study supports previous research showing that increased selenium intake may help prevent the development of prostate cancer.
FIGURE 1 Serum Selenium and Prostate Cancer Literature Review Studies
The study supports “the hypothesis that there is a relationship between serum selenium levels and prostate cancer risk in populations with long-term steady selenium intake. However, selenium measurements in toenail samples and other biomaterials are needed to evaluate short-term and transient changes in selenium intake.”
Of note is that there was strong evidence of heterogeneity among the qualified studies. “Although differences in populations, study design, smoking status, grade, and stage of cancer may explain this heterogeneity, other differences present in the studies should also be considered,” the researchers concluded. They are calling for well-designed cohort studies and randomized controlled studies based on non-Western populations are required."