Brazil nuts are one of the highest natural sources of selenium, with 100g containing 920 µg. The Recommended dietary intake (RDI) for selenium has been set at 70 µg for men and 60 µg for women, however, an upper level of intake has been set at 400 µg /day.  Given we only absorb around 55-70% of selenium from the foods we eat [1], it is not very likely that selenium toxicity will occur. So, enjoying a few Brazil nuts each day is safe and is unlikely to cause any significant adverse effects – just don’t eat excessive amounts all at once.

Brazil nuts are one of the highest natural sources of selenium, but it’s also found in seafood, poultry, eggs and other plant sources such as sunflower seeds and wheat germ. The amount of selenium in plant sources depends on the location, as selenium levels in soil vary. For example, New Zealand soil contains low selenium levels, meaning that dietary intakes and selenium status are lower than in many other countries [2]. 

An upper level of intake (UL) has also been set at 400 µg of selenium a day and relates to intakes from food and supplements [3]. This is based on studies from China and the US indicating that intakes of 800 µg does not cause adverse effects. Studies in native populations of the Brazilian Amazon region have found blood selenium levels ranging from 103 to 1500 µg with no signs or symptoms of selenium toxicity [4]. However, because of gaps in the body of evidence, a safety factor is applied – resulting in an upper limit of 400 µg (equivalent to 43g or approximately 15 Brazil nuts).

There is limited data about selenium toxicity in humans but the most common outcomes are brittleness and loss of hair and nail, as well as gastrointestinal disturbance, skin rash, fatigue, irritability and nervous system abnormalities. 

So, enjoying a few Brazil nuts each day is safe and is unlikely to cause any significant adverse effects, just don’t eat excessive amounts all at once.

References

  1. Whanger, P.D., Metabolism of selenium in humans. The Journal of Trace Elements in Experimental Medicine, 1998. 11(2‐3): p. 227-240.
  2. Thomson, C.D., et al., Brazil nuts: an effective way to improve selenium status. Am J Clin Nutr, 2008. 87(2): p. 379-84.
  3. National Health and Medical Research Council. Nutrient Reference Values for Australia and New Zealand 2005.
  4. Lemire, M., et al., No evidence of selenosis from a selenium-rich diet in the Brazilian Amazon. Environ Int, 2012. 40: p. 128-136.
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