High and low selenium exposure and cancer risk: a meta-meta-analysis

Selenium was discovered in the first quarter of the 19th century and classified as a chalcogen belonging to the 16th group, along with oxygen, sulfur, tellurium, and polonium. Selenium plays a role in the activation of antioxidant enzymes in the body and helps reduce oxidative stress by preventing cell damage. It is believed to have cancer-protective effects, including mechanisms such as reducing DNA damage, regulating cell growth, supporting the immune system, and engaging in epigenetic interactions. These are attributed to the antioxidant properties of selenium. The purpose of this paper was to investigate the effect of selenium exposure on the incidence and mortality of various cancer types utilizing the meta-meta-analysis method. A comprehensive and systematic literature search was performed using renowned databases including PubMed/Medline, Web of Science (WoS), and Scopus. The search utilized predefined keywords to ensure a comprehensive exploration of the subject matter. A total of 22 reports from 16 eligible meta-analyses met the inclusion criteria in assessing the risk of selenium exposure in relation to cancer incidence and mortality. In the pooled analysis of 18 reports from a total of 16 meta-analyses evaluating selenium exposure and cancer risk, higher selenium exposure was associated with a 22% lower risk of cancer (OR = 0.78, 95% CI: 0.72-0.85, p < 0.001). Similarly, in the pooled analysis of four meta-analyses evaluating selenium exposure and cancer-related mortality, higher selenium exposure was associated with lower mortality (RR = 0.88, 95% CI: 0.83-0.94, p < 0.001). This highlights the potential beneficial effects of selenium in reducing cancer-related mortality. This paper also suggests that higher levels of selenium exposure may be an effective strategy for the prevention and management of cancer. The findings support the potential role of selenium in cancer prevention and highlight its importance as a possible intervention for improving health outcomes in individuals at risk of cancer.