Selenium is a chemical element and an essential trace mineral needed only in small quantities. The cells combine selenium and proteins together into a molecule called selenoproteins to help regulate thyroid function and the immune system. As an antioxidant, selenoproteins also prevent cellular damage. The relationship between selenium and lung cancer is unresolved as of June 2011, but some studies indicate that low levels of selenium may represent a risk factor for the disease.
Dietary Sources
The major dietary source of selenium is plant-based foods. However, the content of selenium depends mostly on the selenium content of the soil in which the plants grow. Animals that eat plants grown in selenium-rich soil also contribute to the selenium in meat and seafood. The average daily recommended intake for an adult is only 55mcg per day. By comparison, 1 oz. of dried Brazil nuts contains 544mcg. Tuna, beef, noodles, cod, turkey, chicken, rice, bread, eggs and oatmeal are also important sources. Health companies sell selenium separately as a dietary supplement.
Research
Several studies, though not always consistent, have demonstrated a tangible relationship between selenium levels and lung cancer, including one which found that 200mcg of selenium a day significantly reduced the rate of the disease. Not all studies have found a relationship. However, the rate of certain kinds of cancer is significantly higher in areas of the United States with low selenium soil content. Even when adjusted for the incidents of smoking, very low selenium status still appears to contribute to the risk of lung cancer.
Supplementation
Cancer is a complicated disease with multiple potential causes. Nevertheless, a 2004 study published in the journal "Cancer Epidemiology, Biomarkers and Prevention" suggests that increased selenium intake or supplementation "may have some protective effect against lung cancer in populations where average selenium levels are low." Future research is still needed to further solidify these findings before a greater consensus emerges.
Effects
Researchers have discovered two different ways in which selenium may affect the risks of cancer. Selenium has antioxidant properties that can protect cells from the kind of damage that would normally lead to cancer. In more recent years, studies have also found that selenium may prevent or slow the growth of tumors directly by enhancing immune system activity and suppressing the development of blood vessels to the tumor.
References
- Office of Dietary Supplements; Selenium; November 2009
- "Cancer Epidemiology, Biomarkers and Prevention"; Selenium and Lung Cancer: A Quantitative Analysis of Heterogeneity in the Current Epidemiological Literature; Hanjing Zhou, et al.; May 2004
- "American Journal of Epidemiology"; Is Low Selenium Status a Risk Factor for Lung Cancer?; P. Knekt, et al.; November 1998
