A handful of nuts with an evening movie - for many, this is part of the enjoyment. Brazil nuts are particularly popular. They provide important selenium for our immune system. But there are also warnings circulating on the internet. The nuts contain radioactive radium and other harmful substances. Researchers from Dresden have now carried out precise measurements. Their answer is reassuring.
"Our study confirms the exceptionally high selenium content in Brazil nuts," says Dr. Astrid Barkleit from the Helmholtz-Zentrum Dresden-Rossendorf. Just one nut covers the daily requirement of this important trace element. Selenium strengthens the immune system and protects the cells. Barkleit's team found that around 85 percent of selenium is released during digestion. The body can therefore absorb it well.
The problematic companions remain bound
However, Brazil nuts also store other elements. The trees absorb barium and radioactive radium from the mineral-poor soils in the South American rainforest. Both substances can be stored in bones. That sounds threatening. The good news is that these substances remain almost completely bound when we eat. Only around two percent dissolve in the digestive tract and enter the body.
"Even eating a Brazil nut every day results in a radiation dose of only around 2.4 microsieverts per year," explains Dr. Diana Walther from VKTA Rossendorf. That is only a thousandth of the natural radiation we are exposed to in Germany anyway. By comparison, a flight from Frankfurt to New York generates around 50 microsieverts.
Plant shields prevent absorption
The researchers tested what happens during digestion in the laboratory. They mixed crushed Brazil nuts with artificial saliva, gastric juice and digestive enzymes. They discovered the protective mechanism: the nuts contain phytic acid. This plant-based compound binds metals firmly to itself. This prevents barium and radium from entering the body.
The Dresden team also investigated other trace elements such as strontium and rare earth elements using various spectroscopic methods. Here, too, the all-clear was given. The quantities are far below critical levels. The researchers conclude: Brazil nuts remain a valuable food. The toxic elements they contain play practically no role in normal consumption.
