Selenium is a trace element that is naturally present in many foods, added to others, and is available as a food supplement. This nutrient is essential for humans and plays a critical role in reproduction, thyroid hormone metabolism, DNA synthesis, and protection from infection and oxidative damage. Both the organic and the inorganic forms can be good dietary sources of selenium.
So should you take a selenium supplement? I must admit that I am confused. A large (the SELECT) study showed that taking selenium to science higher selenium levels did not reduce the risk of prostate, colon, of lung cancer (JAMA 2011; 306:1549). Yet other data has not supported such a negative conclusion. In a study from the Netherlands of over 58000 men ages 55 to 69, those who had a higher selenium level (as measured in the toenails, a better measure of long-term selenium levels) reduced prostate cancer by 59%. A follow-up meta-analysis (study of studies) also confirmed that higher selenium levels reduced the risk of prostate cancer (American J of Clinical Nutrition 2012; 96:111-122).
Am I in a Group with a Risk of Selenium Deficiency? Selenium deficiency is rare in the USA and Canada, but some groups may be at higher risk, including: 1) those undergoing kidney dialysis; 2) people with HIV; and 3) those living in selenium-deficient regions (certain parts of China; some European countries, especially populations consuming vegan diets).
My Take: Following the SELECT study, I stopped endorsing selenium supplements for those at a high risk for getting prostate, lung, or colon cancer. The recent data and meta-analysis suggests that selenium may be beneficial. Still, given the absence of compelling, high-level evidence to take selenium supplements, I will skip the supplements and stick to my brazil buts (6 to 8 nuts gives you over 750% of the US recommended daily amount), tuna (yellowfin, cooked with dry heat, 3 ounces; 131%), halibut (67%), sardines, ham, shrimp, macaroni (1 cup, 53%), chicken (light near roasted, 3 ounces; 31%) and other foods. I’m Dr. Michael Hunter, and I think I’ll head to lunch (as all this food talk is making me hungry!).
Other Reference: http://ods.od.nih.gov/factsheets/Selenium-HealthProgressional/