How Selenium Helps Protect Against Cancer

The Physicians Committee
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How Selenium Helps Protect Against Cancer

Selenium is a powerful mineral. Needed only in very small amounts, it plays a crucial role in your cells' defenses against cancer. It is a central part of the enzymes that knock out free radicals, the unstable molecules that can attack your cells and ultimately lead to cancer. It also plays a role in recycling antioxidants through the body. These antioxidants, such as vitamin E, then lower the risk of cancer by preventing free radicals from damaging cells.

Selenium may also protect the body against contaminants such as mercury, cadmium, and silver, help speed the elimination of cancer cells, and slow tumor growth.1 A selenium deficiency is very serious and can cause nerve and heart dysfunction. Fortunately, most people in the world get plenty of selenium, except, perhaps, in unusual areas where soil selenium is low and food fortification is inadequate.

Studies have shown that selenium intake above the recommended dietary allowance (RDA), while not necessary for normal body function, may protect against certain cancers. In one region of China, where epidemic rates of esophageal and gastric cancers occurred, the risk was cut in half after large dose of selenium were given.2 In populations at higher risk for prostate cancer, selenium supplements decreased risk and growth rate of tumors.3 Selenium supplements may also be able to halt the growth of polyps in the colon and reduce the risk of lung and liver cancers.4,5 However, it's still best to get your selenium from foods, because too much can be toxic.

Food Sources

The richest sources of selenium are cereals, grains, and Brazil nuts. Vegetables and fruits also provide small amounts of selenium. How much we consume is almost entirely dependent on levels of selenium in the soil where crops are grown. Fortunately, for U.S. residents and those who consume exported U.S. foods, there is generally enough in the soil to promote health. The amount of selenium needed for normal body function is only 40 micrograms per day with the RDA being 55 micrograms. Intakes of most U.S. residents easily surpass both of these values. Countries that remain at risk for selenium deficiency are China, Denmark, Finland, and New Zealand. So, if you are consuming food grown mostly in the United States, you probably don't need to worry about selenium.5

Tips for Increasing Selenium in Your Diet

While the U.S. RDA for selenium is 55 micrograms, studies show that for maximum protection against cancer, intake of selenium as high as 100 to 300 micrograms per day is necessary. To increase your intake of selenium for maximum cancer protection, base your meals on a variety of grains. For an added bonus have a serving of tofu (40 micrograms) or a single Brazil nut (120 micrograms).


1. Yoon SO, Kim MM, Chung AS. Inhibitory effect of selenite on invasion of ht1080 tumor cells. J Biol Chem. 2001;276:20085-20092.

2. Mark SD, Qiao Y, Sanford DM, et al. Prospective study of serum selenium levels and incident esophageal and gastric cancers. J Natl Cancer Inst. 2000;92:1753-1763.
3. Costello AJ. A randomized, controlled chemoprevention trial of selenium in familial prostate cancer: Rationale, recruitment, and design issues. Urology. 2001;57(Suppl):182-184.
4. Chigbrow M, Nelson M. Inhibition of mitotic cyclin B and cdc2 kinase activity by selenomethionine in synchronized colon cancer cells. Anticancer Drugs. 2001;12:43-50.
5. Combs GF Jr. Selenium in global food systems. Br J Nutr. 2001;85:517-547.