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Brazil nuts are known as “selenium bombs” and are consumed as a natural dietary supplement. However, they do not only contain this essential nutrient, but also traces of potentially problematic metals like barium and radioactive radium. Researchers at the Helmholtz-Zentrum Dresden-Rossendorf (HZDR) and the VKTA – Radiation Protection, Analytics & Disposal Rossendorf Inc. have now conducted the first systematic study on the amounts of these elements that could actually enter the body during the digestive process. The team has some good news for lovers of the nut-like seed (DOI: 10.3390/ijms26178312).
Brazil nuts are an especially nutrient-rich source of food: they contain important minerals like calcium and magnesium, essential amino acids and unsaturated fatty acids. Brazil nuts are characterized by very high selenium levels, an essential trace element that supports the immune system and protects cells from oxidative stress. A single Brazil nut can cover the recommended daily requirement of 55 to 70 micrograms.
“Our study confirms the extremely high selenium content in Brazil nuts. At the same time, we were also able to show that around 85 percent of the selenium is released during digestion and can then be taken up by the body,” says Dr. Astrid Barkleit from the Institute of Resource Ecology at HZDR, summarizing a core finding in the study.
Using nuclear magnetic resonance spectroscopy (NMR) the researchers identified the main form of selenium in the nuts: selenomethionine, an amino acid that is particularly well absorbed by the body. Thus, Brazil nuts really provide a selenium compound that is of high value to the human organism.
Unexpected companions
Besides the healthful nutrients, Brazil nut trees also extract and store other elements from the soil. Because the soils in the South American rainforests – home to the trees – are relatively low in calcium, chemically similar elements like barium and radium partially replace the calcium. Similar to calcium, these metals can accumulate in bones and potentially cause harm. Radium, for instance, is radioactive and thus suspected of causing bone damage and increase cancer risk. However, the study revealed that both substances are barely dissolved in the digestive tract. Merely about two percent of barium and radium in the nut kernel are bioavailable, that is, released in the digestive tract.
“The calculations show that, due to the very low bioavailability, a daily consumption of one Brazil nut would result in a radiation dose of about 2.4 microsieverts per year. That is only about a thousandth of the natural annual radiation exposure in Germany which is given to 2.1 millisieverts per year on average by the Federal Office for Radiation Protection. Of this, about ten percent are ingested with food. Therefore, the radiation exposure caused by radium in Brazil nuts is significantly less than previously assumed,” explains Dr. Diana Walther from VKTA.
The researchers suspect that the low solubility is due to substances the plant stores in its seeds: They found phytic acid, which binds minerals and metals strongly and thus prevents the body from absorbing them.
They analyzed other trace elements like strontium, lanthanum and europium. Strontium behaves chemically similar to calcium and is bioavailable to approximately 50 percent, however, only present in such small amounts that it is not toxicologically relevant. Lanthanum and europium belong to the so-called rare earths and were detected in only smallest amounts. Their bioavailability is about 25 percent, however, the intake levels remain well below the established limit values.
This is because not every element in a food is actually absorbed by the body. The decisive factor is how much is released during digestion – this fraction is considered as “bioavailable.” To test this, the researchers simulated the digestion process in the lab using artificial saliva, gastric juice and digestive enzymes at body temperature. This allowed them to see which substances dissolve and could potentially be absorbed by the small intestine.
Very modern analytics for an ancient food
The team used mass spectrometry to determine the concentrations of the elements, gamma and alpha spectrometry for radioactive isotopes, and NMR and laser fluorescence methods for characterizing the chemical binding form of the elements.
Moreover, the researchers were interested in discovering whether components of the Brazil nut influence the efficacy of so-called decorporation agents – compounds that are used to remove radioactive material in cases of contamination from the body. The results showed that the composition of Brazil nuts only had a minimal impact on the efficacy of these substances.
“Our results confirm that Brazil nuts are a valuable food – especially as a natural source of selenium,” Barkleit summarizes. “At the same time, they show that, thanks to their low solubility, the potentially harmful elements they contain hardly affect the body when the nuts are consumed.”
This work was funded by the Federal Ministry of Research, Technology and Space (BMFTR) within the collaborative project RADEKOR (grant numbers 02NUK057A and D).
Publication:
A. Barkleit, J. Eum, D. Walther, D. Butscher, S. Friedrich, K. Müller, J. Kretzschmar, In Vitro Bioaccessibility and Speciation of Toxic and Nutritional Trace Elements in Brazil Nuts, in International Journal of Molecular Sciences, 2025 (DOI: 10.3390/ijms26178312)
Additional information:
Dr. Astrid Barkleit
Institute of Resource Ecology at HZDR
Phone: +49 351 260 3136 | Email: a.barkleit@hzdr.de
Dr. Diana Walther
VKTA – Radiation Protection, Analytics & Disposal Rossendorf Inc.
Phone: +49 351 260 2124 | Email: Diana.Walther@vkta.de
Media contact:
Simon Schmitt | Head
Communications and Media Relations at HZDR
Phone: +49 351 260 3400 | Mobile: +49 175 874 2865 | Email: s.schmitt@hzdr.de
The Helmholtz-Zentrum Dresden-Rossendorf (HZDR) performs – as an independent German research center – research in the fields of energy, health, and matter. We focus on answering the following questions:
• How can energy and resources be utilized in an efficient, safe, and sustainable way?
• How can malignant tumors be more precisely visualized, characterized, and more effectively treated?
• How do matter and materials behave under the influence of strong fields and in smallest dimensions?
To help answer these research questions, HZDR operates large-scale facilities, which are also used by visiting researchers: the Ion Beam Center, the Dresden High Magnetic Field Laboratory and the ELBE Center for High-Power Radiation Sources.
HZDR is a member of the Helmholtz Association and has six sites (Dresden, Freiberg, Görlitz, Grenoble, Leipzig, Schenefeld near Hamburg) with almost 1,500 members of staff, of whom about 700 are scientists, including 200 Ph.D. candidates.
Dr. Astrid Barkleit
Institute of Resource Ecology at HZDR
Phone: +49 351 260 3136 | Email: a.barkleit@hzdr.de
Dr. Diana Walther
VKTA – Radiation Protection, Analytics & Disposal Rossendorf Inc.
Phone: +49 351 260 2124 | Email: Diana.Walther@vkta.de
A. Barkleit, J. Eum, D. Walther, D. Butscher, S. Friedrich, K. Müller, J. Kretzschmar, In Vitro Bioaccessibility and Speciation of Toxic and Nutritional Trace Elements in Brazil Nuts, in International Journal of Molecular Sciences, 2025 (DOI: 10.3390/ijms26178312)
https://www.hzdr.de/presse/brazil_nut
Spectroscopic methods, such as laser fluorescence spectroscopy, can be used to determine the chemica ...
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Spectroscopic methods, such as laser fluorescence spectroscopy, can be used to determine the chemica ...
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