[Selenium] Selenium content in Brazil nuts varies greatly – Should Brazil nuts still be considered a reliable and safe source of selenium?

Selenium is an important mineral for general health and is of particular importance in the prevention of cancer or its relapses.
I knew Brazil nuts are an easy high source of selenium and I wondered “Can people reliably and safely get their selenium from Brazil nuts?
For those in a hurry, the answer is: It’s possible but not reliably.

Brazil nuts have very random amounts of selenium in them. From close to nothing at all, to 20 times the RDI* (Recommended Daily Intake), the RDI being ~65 microg/g for adults.[4]

Variation of selenium content in Brazil nuts

The following three studies show just how random the content of selenium in Brazil nuts can be:

“The average and standard deviation and range of selenium concentrations in ppm, fresh weight for nuts from [the two] regions were, respectively, 3.06 ± 4.01 (0.03–31.7) and 36.0 ± 50.0 (1.25–512.0).” [1]
Another study looked concluded that “concentrations were highly variable (median: 13.9 microg/g; range: 0.4-158.4 microg/g). [2]”
In another study, they wanted to compare selenium form nuts and from supplements. But in trying to measure the exact amount of selenium they wanted from nuts they faced “difficulties in analyzing individual nuts” because the “first 10 nuts [were] ranging from 0.816 to 1390 microg Se/g”. [3]

Content variation, a widely ignored reality in nutrition and plant medicine

As I explained in my previous post about green tea, the content of specific compounds in organic products is known to vary greatly, while too often overlooked. The presence and wide usage of nutritional facts databases for fruits and vegetables is a good example of the lack of general understanding of this variation. With variations from nil to 20 times the RDI as is the case for Brazil nuts, you would expect a gigantic red asterisk next to virtually every number on those websites. This would remind the general public that the numbers mean absolutely nothing, that they are averages of a wide range, that the quantifying was done on a single fruit/vegetable/nut or that the sample is non-representative of the real life consumption. However, such variations are the main reason for inconsistencies in efficiency of herbal products in herbal medicine, and sometimes for the lethality of treatments/foods otherwise very effective and safe. Many people today would rather get their nutrients from food and cures from plants rather than from supplements and drugs respectively. The good thing however about (reliable brands of) supplements is that unlike in foods and plant medicine, the dosage of active ingredient is measured, consistent and reliable.

Questioning the reliability and safety of Brazil nuts as a health-promoting food

Given the tremendous variations reported about selenium, it is fair to address the following questions:

  1. How does the variation in selenium content affect blood selenium?
  2. Is there a risk in having even a single small intake of the nuts highest in selenium?
  3. Supposing we vary sources, does nuts selenium (and therefore blood selenium) average to healthy levels?

This is all to answer the question: Are Brazil nuts a safe and reliable method of ensuring a healthy intake of selenium?

Note to readers: The study annotated “[2]” is led by a French team that has published several papers on selenium and Amazonian populations and may be the first most relevant direction for further study on the subject.

* RDIs are very arguable.


[1] “Selenium content of Brazil nuts from two geographic locations in Brazil”, (Jacqueline C. Chang & al., 1994)
[2] “Elevated levels of selenium in the typical diet of Amazonian riverside populations”, Sci Total Environ. 2010 Sep 1;408(19):4076-84. doi: 10.1016/j.scitotenv.2010.05.022.
[3] Brazil nuts, an effective way to improve selenium status (Thomson & al, 2008)
[4] Selenium – New Zealand Nutrition Foundation

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