Selenium

Selenium (Se) is an essential trace element found in the soil, water, and some foods, such as select nuts, fish, meat, and grains. Selenium is essential to human health due to its antioxidant properties and benefits metabolism. In 2017, Steven Owen Evans et al. stated, "Extensive study of selenium compounds has demonstrated growth inhibition of malignant cells in a vast array of experimental models." They reported that "Se affects varied cellular processes and molecular pathways that may be involved in the anti-cancer effect of Se." These included:

  • Seleno-enzymes involving the reduction of DNA damage, oxidative stress, and inflammation;

  • Induction of phase II conjugating enzymes involving detoxifying carcinogens and reducing DNA adduct formation;

  • Enhancement of immune response, including cytotoxic lymphocyte and natural killer cell activity;

  • Increase in tumor-suppressor protein, which inhibits proliferation, stimulates DNA repair, and promotes apoptotic death by acting as a transcription factor for several genes, including the growth arrest and DNA damage-inducible (GADD) genes;

  • Inactivation of protein kinase C, a signaling receptor that plays a crucial role in tumor promotion by oxidants;

  • Alteration in DNA methylation, as abnormal methylation patterns are associated with neoplasia and inactivation of tumor-suppressor genes;

  • Perturbation of the cell cycle, resulting in growth inhibition, and may allow DNA repair to take place;

  • Induction of apoptosis of cancer cells, which generally involves the sequential activation of the caspases;

  • Inhibition of angiogenesis is required for the growth and metastasis of tumors.

In addition, in 2016, Xianlei Cai et al. conducted a meta-analysis of studies conducted on selenium and cancer. The researchers "looked at 69 studies and applied meta-analysis, meta-regression, and dose-response analysis to obtain available evidence. The results indicated that high selenium exposure had a protective effect on cancer risk (pooled OR = 0.78; 95%CI: 0.73–0.83). The results of linear and nonlinear dose-response analysis indicated that high serum/plasma selenium and toenail selenium had the efficacy on cancer prevention." They found that selenium decreased the risk of breast cancer, lung cancer, esophageal cancer, gastric cancer, and prostate cancer.