Is One Brazil Nut a Day Okay? Evaluating the Selenium and Radium Intake from Brazil Nuts

"Selenium Bomb" Brazil Nuts: It's Not the Quantity but the Dissolution That Matters

Brazil nuts are a staple among nutrition enthusiasts as a "natural supplement." They are particularly noted for their selenium (Se) content, an essential trace element involved in immunity and antioxidation. Brazil nuts have been known as a food that "yields a lot from a small amount." However, the same nuts also contain barium (Ba) and radioactive radium (Ra), and depending on soil conditions, they can be introduced as "highly radioactive foods."

Here's a common pitfall for many people.
"Contained" does not equal "absorbed by the body."
Elements contained in food must dissolve during digestion to be absorbed in the small intestine. Without considering how much they "dissolve" (bioaccessibility: the proportion that becomes absorbable through digestion), health impacts cannot be evaluated.

Researchers have seriously measured this "dissolution." A team from the Helmholtz-Zentrum Dresden-Rossendorf (HZDR) and VKTA in Germany systematically investigated the proportion of both nutritional and harmful elements in Brazil nuts that could enter the body during digestion. phys.org

Experiment: Simulating "Mouth→Stomach→Intestine" in Test Tubes: Focusing on "Dissolution Amount" Rather Than "Total Amount"

The research team used a method (UBM protocol) that simulates digestion by gradually adding artificial saliva, gastric juice, pancreatic juice, and bile while stirring under body temperature conditions. They measured how much each element dissolved from Brazil nuts (including defatted Brazil nut powder used in the study). MDPI

Furthermore, the study delved into "speciation," or the chemical forms in which elements exist, which is a key point.

• Element Concentration: ICP-MS (Mass Spectrometry)

• Radioactive Nuclides: Gamma and Alpha Spectrometry

• Major Form of Selenium: NMR (Nuclear Magnetic Resonance)

• Metal Ion Binding State: Laser Fluorescence (TRLFS)
  ...making it more of a "chemical and radiochemical full-scale battle" than food analysis. phys.org
  
  

Results Are Striking: About 85% of Selenium Dissolves, but Only About 2% of Barium and Radium Dissolve

In conclusion, the evaluation of Brazil nuts leans towards "nutritionally strong" and "less likely to be absorbed radioactively or metallically than imagined."

• Selenium: About 85% Dissolves During Digestion (Becomes Absorbable) phys.org

• Barium: About 2% Dissolves During Digestion phys.org

• Radium (^226Ra, ^228Ra): About 2% Dissolves During Digestion phys.org

The "form" of selenium is also important. NMR analysis and other methods identified the main selenium species as **selenomethionine (SeMet)**, which is generally considered to be easily utilized in the body. The study supports the strength of Brazil nuts in "providing high-value selenium compounds." phys.org

Why Do Brazil Nuts Contain Radium? The Key Lies in "Calcium-Deficient Soil"

Why do Brazil nut trees tend to accumulate radium? According to an article on Phys.org, the soil in the South American tropical rainforest is relatively low in calcium, allowing chemically similar barium and radium to be absorbed by plants as "substitutes" for calcium. phys.org
(The idea that "alkaline earth metals can easily substitute for each other" is intuitive in elemental chemistry.)

However, absorption by plants and absorption by humans when consumed are separate issues. This study distinguished between the two.

The Culprit Behind "Low Absorption": Phytic Acid Firmly Grabs Metals

The research team cites the presence of **phytic acid (phytate)** as a reason for low dissolution. Phytic acid is well-known as a form in which seeds store minerals, and it strongly binds metal ions, often inhibiting human absorption. The Phys.org article also mentions that phytic acid may strongly bind minerals and metals, hindering absorption. phys.org

Interestingly, the research paper discusses that "barium existing only as 'insoluble salts like barium sulfate' may not fully explain the low dissolution," and explores binding with organic substances like phytic acid as a "strong candidate." Elements in food do not exist solely as simple inorganic salts—a subtle but important lesson. MDPI

How Much Radiation? Estimated at 2.4 µSv Annually for "One Nut a Day"

Hearing "contains radioactive radium" can be alarming, but the estimate in this study is quite small.

According to the research team's calculations,long-term consumption of one nut per day results in an additional exposure of about 2.4 microsieverts (µSv) per year. This is about 1/1000th of the average natural radiation in Germany (2.1 millisieverts = 2,100 µSv per year). Additionally, it is explained that about **10% of natural radiation comes from diet**, positioning the impact of radium from Brazil nuts as smaller than previously thought. phys.org

The important point here is not whether it's "zero," but "where it stands in comparison." This scale at least distances us from the simplistic notion of "immediate danger because it contains radium."

However, the main caution is selenium: Limits Vary by Country and Organization

The idea that "selenium overdose is more realistic than radioactivity" has been around for a while, but the fact that "85% dissolves" is significant this time.

Selenium is essential but also a nutrient with a "narrow intake range." According to the NIH (U.S.) supplement information, the tolerable upper intake level (UL) for adults is 400 µg/day, and chronic excess can lead to hair loss and nail brittleness (selenosis). Brazil nuts are particularly high in selenium, with data showing an average of 544 µg in one ounce (6-8 nuts). Office of Dietary Supplements

On the other hand, the EFSA (European Food Safety Authority) sets the UL for adults at 255 µg/day based on evaluations (lower than the U.S. 400 µg). Summary information available in Japanese also shows this 255 µg/day. efsa.onlinelibrary.wiley.com

In other words, "how many nuts are safe" depends on

• the variation in selenium content per nut (which varies by origin and soil)

• the individual's diet (additional intake from fish, meat, eggs, supplements)

• which standard (U.S. 400 or European 255) is adopted
  , causing the answer to fluctuate.

In the research paper, assuming one nut per day (about 5g), the estimated range incorporates the variation in selenium content and 85% dissolution, suggesting it falls below the European UL (255 µg/day). However, given the large variability in commercially available nuts, "not overeating daily" and "monitoring total intake if using supplements" are practical approaches. MDPI

Other Elements: Strontium Dissolves Easily but Is in Small Amounts / Rare Earths Are in Trace Amounts

The study also measured strontium (Sr), lanthanum (La), and europium (Eu).

• **Strontium: Bioaccessibility of About 50%** but its content is small, making it unlikely to be a toxicological issue phys.org

• Lanthanum and Europium: About 25% Dissolves, but detection amounts are minimal, and intake is well below existing limits phys.org
  
  

Does "Medicine to Remove Contaminants" Work? The Impact of Food Matrix Is Minimal

Though somewhat specialized, this study also touches on "decorporation agents." These are chelating agents (such as EDTA, DTPA, HOPO) that promote the excretion of radioactive substances if they enter the body. The study examined whether components from Brazil nuts weaken their effectiveness using TRLFS, suggesting that the impact of the food matrix is minimal. While not directly related to everyday meals, it is interesting that the study examined whether "food-element binding" affects medical strategies using the same experimental system. MDPI

##HTML_TAG