Brazil nuts are the most highly concentrated source of selenium. In fact, scientists have shown that a daily Brazil nut is a better source of the mineral than taking a supplement. New Zealand researchers compared Brazil nuts' efficacy to that of selenomethionine supplements in increasing selenium status in 59 New Zealand residents with low selenium (plasma selenium concentrations < 1.27 micro mol/L).
Participants were randomly assigned to one of three groups. One group ate two Brazil nuts each day (estimated to provide approx. 100 micrograms Se). A second group took a supplement providing 100 micrograms of selenium as selenomethionine per day, and the third group, who served as controls, were given a placebo pill. Blood levels of selenium and glutathione peroxidase (GPx - a selenium containing enzyme that is one of the body's most important antioxidants) activities were measured at the beginning of the study and at 2, 4, 8, and 12 weeks.
By week 12, blood levels of selenium had increased by 64.2%, 61.0% and 7.6%, respectively, in the Brazil nut, selenomethionine, and placebo groups. Plasma levels of GPx increased by 8.3%, 3.4% and -1.2%, and whole blood GPx by 13.2%, 5.3% and 1.9% in the Brazil nut, selenomethionine and placebo groups, respectively.
Not only was consumption of two Brazil nuts each day as effective for increasing selenium status and enhancing GPx activity as 100 micrograms of selenomethionine per day, but just one Brazil nut per day would have been sufficient to raise dietary selenium intake to within recommended intake levels for the mineral.