Selenium is a mineral with anti-cancer properties. Many studies in the last several years have shown that selenium is a potent protective nutrient for some forms of cancer. The Arizona Cancer Center posted a selenium fact sheet listing the major functions of selenium in the body . These functions are as follows:

  1. Selenium is present in the active site of many enzymes, including thioredoxin reductase, which catalyze oxidation-reduction reactions. These reactions may encourage cancerous cells to under apoptosis.
  2. Selenium is a component of the antioxidant enzyme glutathione peroxidase.
  3. Selenium improved the immune systems' ability to respond to infections.
  4. Selenium causes the formation of natural killer cells.
  5. P450 enzymes in the liver may be induced by selenium, leading to detoxification of some carcinogenic molecules.
  6. Selenium inhibits prostaglandins that cause inflammation.
  7. Selenium enhances male fertility by increased sperm motility.
  8. Selenium can decrease the rate of tumor growth.

A double-blind, controlled trial of a 200 µg/day selenium supplement in the southeastern region of the USA (where soil selenium levels are low) found that the primary endpoints of skin cancer were not improved by the selenium supplement, but that other cancer incidence rates were decreased by selenium. There was a significant reduction in total cancer incidence cases, prostate cancer, a marginally significant reduction in colorectal cancer incidence, and a reduction in cancer mortality. The selenium supplement was most effective in ex-smokers and for those who began the study with the lowest levels of serum selenium.

Overall, it appears that poor selenium levels, especially for men, are a cancer risk. If a person has low selenium levels and other antioxidant defenses are also low the cancer risk is increased even further. Women do not appear to be as sensitive to selenium, as breast cancer has not been found to be influenced by selenium status in several studies, although both men and women were found to be protected by higher levels of selenium from colon cancer and lung cancer . Good vegetarian sources of selenium are whole grains and legumes grown in selenium-rich soil in the western United States, brazil nuts (by far the most dense source of selenium), nutritional yeast, brewers yeast, and sunflower seeds. (Adapted from "Nutrition and cancer: A review of the evidence for an anti-cancer diet. Nutrition Journal 2004, 3:19doi:10.1186/1475-2891-3-19")

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