Cancer Nutrition Network for Texans
What is it?
Selenium is an essential trace element which occurs naturally in soil. It enters our bodies through our food. Plants absorb selenium from the soil into their leaves, stems, seeds and fruits. Animals eat plants containing the selenium and this is stored in their tissues. The best sources of selenium are shellfish, whole grains, brazil nuts, vegetables, eggs and chicken.
How does it work?
Although the exact mechanism of action of selenium is not known, selenium is an important component of substances in the cell which are responsible for scavenging free radicals that are formed from the metabolism of oxygen in the cells in your body. Selenium is active in several enzymes, such as thioredoxin reductase and glutathione peroxidase which help prevent a process called oxidation which may cause injury to the cells in your body. Selenium may increase production of certain enzymes in the liver, such as P450, which are responsible for detoxifying some cancer causing substances. Selenium also inhibits prostaglandins, a substance which causes inflammatory reactions in the body. At high doses, selenium may decrease the rates of tumor cell growth.
Is it effective?
A ten year cancer prevention trial at the University of Arizona suggests that dietary selenium supplementation may significantly lower the incidence of prostate, colorectal and lung cancer. The patients in this study took a tablet containing 200 micrograms of selenium as brewer’s yeast. Some studies have shown an inverse association with the incidence of cancers of the lung, colon, bladder, rectum, breast, pancreas and ovary. However, several studies have shown no association between selenium and cancer and a few have shown an increased cancer risk. The toxicity levels for selenium have not been definitely established.
What is the state of the science?
The National Cancer Institute is currently conducting the first double blind cancer prevention trial to test whether nutritional supplementation alone can reduce cancer risk. Stay tuned and look for further information in N-Sights as soon as new developments are released.
Note: If you would like a list of references for this topic, please write: Educational Cancer Center: 700 Harborside Drive Ewing Hall Room 1.134: Galveston, TX 77555-1147.
Barbara Pence, Ph.D., is the Associate Vice President for Research and Associate Dean for Research and the Graduate School at Texas Tech University Health Science Center.