Selenium is an essential mineral that plays a part in growth and reproduction and helps keep your liver, heart, and muscles in good working order. What's more, research has suggested that it may protect you against cancer. It's a potent antioxidant, clearing the body of free radicals, unstable oxygen molecules that can cause the DNA damage that leads to tumors. And it's been shown in the laboratory to break down carcinogens and induce injured cells to self-destruct before they turn cancerous.

The government currently recommends that both men and women get 55 micrograms a day to avoid selenium deficiency. Pregnant women need 60 mcg daily; breastfeeding mothers need 70 mcg. However, in a 1996 study, people who took 200 mcg a day for seven years ended up with half as many prostate, lung, and colon cancers as those who took dummy pills. The numbers of cancers were too small to be conclusive, however, and more recent studies have had conflicting results. In fact, a large-scale randomized placebo-controlled trial studying the effects of selenium and vitamin E on prostate cancer concluded in October 2008 that selenium did not prevent prostate cancer in relatively healthy men. The study was halted early because of concerning (but not statistically significant) trends showing that there were slightly more cases of diabetes in men taking only selenium and slightly higher levels of prostate cancer among men taking only vitamin E.

If you're like most Americans, you probably get about 100 mcg of the mineral a day from food -- half from bread and cereal and half from milk, eggs, meat, and fish. A small chicken breast (3.5 oz.) contains about 20 mcg; an egg, 14 mcg; and a slice of whole wheat bread, about 10 mcg. Some health food stores now sell soybeans that are grown in selenium-rich soil. Brazil nuts are the richest source; just one packs up to 100 mcg if it's sold in the shell.

Until more is known about selenium, the American Cancer Society recommends eating a variety of healthy foods instead of relying on supplements. A normal diet provides more than enough selenium to keep you healthy, but it still falls short of the dose used in the cancer study. Unless you're crazy about Brazil nuts, a supplement is the only way to hit 200 mcg a day. You might want to talk to you doctor about whether your family history puts you at particular risk for cancer. If you choose to take a supplement, look for an organic formulation made from amino acids or baker's yeast. Synthetic versions may contain an unreliable dose.

The government warns adults against taking more than 400 mcg a day, and children should take much less. More than that can result in skin rashes, fragile fingernails, hair loss, nausea, and diarrhea, eventually leading to liver and respiratory problems and even death.

Further Resources

Varro E. Tyler, PhD. Herbs of Choice: The Therapeutic Use of Phytomedicinals. Pharmaceutical Products Press, 1994.

Andrew Weil, M.D. Natural Health, Natural Medicine. Houghton Mifflin, 1995, 1998.

References

American Cancer Society. Selenium. 2007. http://www.cancer.org/docroot/ETO/content/ETO_5_3X_Selenium.asp?sitearea=ETO

Lippman, SM, et al. Effect of Selenium and Vitamin E on Risk of Prostate Cancer and Other Cancers: The Selenium and Vitamin E Cancer Prevention Trial (SELECT). Journal of the American Medical Association. December 9, 2008.

National Cancer Institute. Selenium and Vitamin E Cancer Prevention Trial (SELECT). October 31, 2008, updated December 9, 2008.

Office of Dietary Supplements. Selenium. April 2009. http://dietary-supplements.info.nih.gov/factsheets/selenium.asp

Last updated October 29, 2009
Copyright © 1998 Consumer Health Interactive and OneBody, Inc.

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