The Study
Natural variation of selenium in Brazil nuts and soils from the Amazon region.
This study looked at how much selenium is in Brazil nuts and the soil they grow in, and found that nuts from some places have way more selenium than others. But it didn't test if the soil makes the nuts that way—it just noticed they go together. So we can say they're linked, but not that one causes the other.
Analysis score
Maximum 44 for a cross-sectional study.
Where the score came from
Brazil nuts get selenium from the soil they grow in, but not all soils have the same amount, and how acidic the soil is also matters.
Where does this study sit?
Reviews of RCTs (Meta-analyses)
Max 100Randomized Trials
Max 90Reviews of Cohort Studies
Max 85Cohort Studies
Max 72Reviews of Case-Control Studies
Max 63Case-Control Studies
Max 58Cross-Sectional & Case Series
Max 50Expert Opinion
Max 542 / 100
Quality score
Snapshots of a population at a single point in time, or descriptions of small groups. Can identify correlations and prevalence, but cannot determine cause and effect.
Key takeaways
Summary
Based on the study abstract and findings.
- 1Because selenium levels vary so wildly by where the nuts are grown, eating Brazil nuts without knowing their origin can mean getting too little or too much selenium — even dangerous amounts.
- 2Nuts from Amazonas had up to 68.15 mg/kg selenium — enough for nearly 3 days' worth in one nut.
- 3Nuts from Mato Grosso had only 2.07 mg/kg — barely 1 day's worth.
- 4Soil selenium ranged from barely detectable to 625.91 μg/kg.
Score breakdown, methodology, conflicts of interest, evidence analysis & raw study data
Publication
Journal
Chemosphere
Year
2017
Authors
Ediu C.Silva Junior, L. Wadt, K. E. D. Silva, Roberval Monteiro, Bezerra de Lima, K. D. Batista, M. Guedes, G. S. Carvalho, Soares de Carvalho, A. R. Reis, G. Lopes, L. R. Guimarães
Related Content
Claims (10)
Brazil nuts from different parts of the Amazon contain different amounts of selenium, so one nut can supply anywhere from 11% to 288% of the daily selenium needs for an adult male, depending on where it was grown.
Brazil nuts grown in the Amazon do not contain dangerous levels of selenium because the soil in that region has selenium concentrations below toxic limits, with the highest recorded level being 625.91 μg/kg.
Brazil nuts from different parts of the Amazon contain different amounts of selenium, so one nut can supply anywhere from 11% to 288% of the daily selenium need for an adult man.
Brazil nuts contain more selenium when they grow in soil with higher selenium levels.
Brazil nuts from different locations contain different amounts of selenium, and where the nuts are grown matters more than the type of tree or its genes.
Brazil nuts absorb less selenium from soil when the soil is more acidic, even if the soil contains high levels of selenium.
Not medical advice. For informational purposes only. Always consult a qualified healthcare professional before making health decisions.