Selenium and Cancer

Tuesday, January 9, 2007 - 4:21pm

By Dena McDowell, MS, RD

Selenium is a micronutrient that is only needed in small amounts in the diet. Since the mid 1980’s this nutrient has been studied to determine how its antioxidant properties help reduce the risk of developing certain disease states such as heart disease and cancer. Research is ongoing, but promising at this point. Eating a balanced diet will help ensure adequate selenium intake. This article describes selenium, food sources and intake related to cancer risk.

Selenium defined
Selenium is a micronutrient and only needed in small quantities in the diet. This mineral plays an integral role in antioxidant production. Selenium plays a role in reducing free production which is protective against cancer cells and heart disease. Selenium helps to regulate thyroid function and the immune system.

Foods rich in selenium
Plants and nuts are the major source of selenium in the diet, however the selenium content of foods is completely dependent on the selenium content of the soil which the plants are grown. People are at risk of selenium deficiency in areas where the soil is depleted of this vital micronutrient. The United States does not have a problem with selenium deficiency due to how our food supply is distributed. Unfortunately in some parts of Russia and China selenium deficiency is commonly seen due to poor soil content and lack of food distribution in these rural areas.

Some meats and seafood are rich in selenium if the animal feed or plant feed was rich in selenium during consumption. Interestingly Brazil nuts contain a large amount of selenium (780% of the daily value). It is recommended that Brazil nuts be eaten sparingly to prevent toxicity. Other foods rich in selenium are tuna, beef, cod, turkey, noodles, eggs, cottage cheese, oatmeal, rice, whole wheat bread and walnuts.

Recommended dietary intake for selenium
As stated above selenium is a micronutrient therefore small amounts are needed in the diet. Children one to three years of age need 20 micrograms a day. Children four to eight years of age need 30 micrograms, whereas children between nine and thirteen years old need 40 micrograms. People fourteen and older need 55 micrograms a day.

Selenium toxicity although rare does exist. Upper limits for selenium are as follows:


Micrograms a day

0-6 months


7-12 months


1-3 years


4-8 years


9-13 years


14 years and older


Selenium and cancer risk
Selenium has been studied since the early 1980’s as a potential anticancer nutrient. Observational studies have shown that those who consumed the largest amount of selenium from the diet had the lowest cancer risk especially in looking at cancer deaths from lung, colon, rectal and prostate. Researchers believe that selenium acts in two ways to reduce cancer risk. First, selenium acts as a free radical scavenger and secondly selenium may reduce risk of tumor cell growth.

Two studies are underway to determine the actual link between selenium intake and cancer risk. In France, the SU.VI.MAX study is looking at the effects of taking antioxidants and chronic disease. Participants in the study receive supplements of antioxidants higher than the recommended doses (selenium is given in 100 microgram daily doses plus dietary intake). 12,000 men and women are enrolled in this trial and results should be published soon.

In the United States the SELECT trial is underway which looks at selenium and/or vitamin E supplementation and prostate cancer risk in healthy men. This is a long term study enrolling over 32,000 men and will conclude in 2013. Men in the study receive 200 micrograms of selenium daily or 200 micrograms and a 400 milligram dose of vitamin E. Research has shown that 200 micrograms of selenium may be the most beneficial dose to prevent certain types of cancers. However the Recommended Dietary Intakes will not change until further research has been completed.

Although selenium only needed in small amounts in the diet it is important to take in adequate amounts on a daily basis to prevent deficiency. Research is ongoing to determine the exact effects of selenium supplementation and chronic disease risk. Early results are promising but current research needs to be completed before further recommendations can be made. Eating a well balanced diet incorporating meat, poultry, seafood, nuts and whole grains will ensure adequate dietary intake. Speak to your health care provider if you have a family history of heart disease or certain cancers to determine if a dietary supplementation of selenium in warranted.