Selenium is naturally found in trace amounts in plant foods, including Brazil nuts, walnuts, and grains (rice, oats, bread, enriched noodles), and animals that graze or eat on plants and grains containing selenium: beef, turkey, dairy products (cheese), eggs, cod and tuna (if canned in oil), and chicken. Selenium has low dietary requirements: daily recommended intake of 55-70 micrograms for individuals over 14 years of age, 15 to 40 micrograms for children, even less in infants. The average intake in the U.S. is >100 mcg.
Regions of Russia and China suffer from selenium deficiency, which has been associated with heart problems, hypothyroidism, a weakened immune system, and cancer, specifically prostate and lung. A 1996 study found that supplementation reduced these two cancers by 30%, but other studies have had contradictory results. In 2008 the National Cancer Institute found that taking selenium and vitamin E does not reduce prostate cancer risk, and evaluating toenail clippings from cancer patients for selenium intake found no correlation with cancer incidence. Yet other studies have shown slowed tumor growth.
A Texas study on lung cancer presented at the June 5, 2010 meeting of the American Society of Clinical Oncology followed 1500 patients with non-small cell lung carcinoma found that those receiving a 200 microgram Selenium regimen did not fare better than those receiving placebo after tumor removal. They halted the trial early in case the supplementation was worsening the patients' condition.
All patients should discuss supplementation with their doctors and treatment professionals. But overall it appears that selenium does not work to reduce or help lung cancer.