A patient consuming large quantities of brazil nuts developed selenium (Se) toxicity and subsequent neurotoxicity. The treating physicians thought you would be interested in a short discussion of Se toxicity.
Se is an essential trace element that is naturally present in many foods, added to others, and available as a dietary supplement. Selenium, which is nutritionally essential for humans, is a constituent of more than two dozen selenoproteins that play critical roles in reproduction, thyroid hormone metabolism, DNA synthesis, and protection from oxidative damage and infection.
Selenium exists in two forms: inorganic (selenate and selenite) and organic (selenomethionine and selenocysteine). Both forms can be good dietary sources of selenium. Soils contain inorganic selenites and selenates that plants accumulate and convert to organic forms, mostly selenocysteine and selenomethionine and their methylated derivatives.
Seafoods and organ meats are the richest food sources of selenium. Other sources include muscle meats, cereals and other grains, and dairy products. The amount of selenium in drinking water is not nutritionally significant in most geographic regions. The major food sources of selenium in the American diet are breads, grains, meat, poultry, fish, and eggs.
(Se deficiency will not be discussed.)
Over time Se is incorporated into erythrocyte proteins, making serum the best measure of acute toxicity. Patients with longtime elemental exposure may have serum concentrations of 0.5-1.0mg/L BUT Se concentrations do not correlate with toxicity. Urinary concentrations are not helpful as excretion of Se is maximal within 4 hours. Hair concentrations are of limited value due to Se occurring in shampoos.
Acute ingestion Se toxicity occurs after ingestion of inorganic Se compounds. Symptoms develop immediately. Initial GI symptoms include nausea, vomiting, diarrhea, abdominal pain which may be caused by esophageal and gastric burns. The myopathic phase follows characterized by weakness, hyoreflexia, myoclonus, fasciculations and increased skeletal CPK. Renal insufficiency results from myoglobinuria and hemolysis. Circulatory failure is the hallmark. Chest pain, dyspnea, tachycardia and hypotension occur. EKG may demonstrate ST elevation and prolonged QT. Death results from circulatory collapse as a result of pump failure, hypotension (decreased peripheral vascular resistance) and ventricular dysrhythmias within four hours of ingestion. There is no antidote or chelation agent and treatment is purely supportive. Outcome is usually fatal.
The most frequent ingestion resulting in acute Se toxicity is that of gun bluing. Children that ingest this suffer cardiovascular collapse within minutes of ingestion. Keep this product out of reach of children. I’ve not seen a child survive following gun bluing ingestion.
Chronic ingestion Chronically high intakes of the organic and inorganic forms of selenium have similar effects. Early indicators of excess intake are a garlic odor in the breath and a metallic taste in the mouth. Chronic Se toxicity or selenosis is similar to arsenic toxicity . The most common clinical signs of chronically high selenium intakes are hair (brittle, breaks at scalp with regrowth discolored) and nail loss or brittleness(fingernails develop ridges). Other symptoms include lesions of the skin (rashes, erythematous, blistered, slow to heal) nausea, diarrhea, mottled teeth, fatigue, irritability, and nervous system abnormalities. Neurologic manifestations include hyperreflexia, peripheral paresthesia, anesthesia and hemiplegia. It is difficult to discern if Se causes neuropsychiatric symptoms.
Se supplements as source of chronic toxicity
Although Se toxicity can occur in the copper refining industry (workers were removed when they had garlic breath prior to workplace biologic monitoring) the most frequent cause of chronic Se toxicity is ingestion of Se containing products such as dietary supplements or health food products.
IN 2008, there was
a manufacturing error in Se-containing dietary supplements that affected more than 200 people. Symptoms included diarrhea, alopecia and nail deformities. FDA investigation revealed that the liquid supplement contained 800 microgramss/L instead of 7.3 micrograms/liter claimed on the packaging. TN Poison Center was one of the poison centers that helped identify this outbreak due to the increased number of calls regarding the nutritional supplement.
As for the brazil nuts?
The recommended dietary allowance per day (RDA) for selenium is 55 mcg for ages greater than 14 years. Brazil nuts are not consistent in their Se content. Each nut contains 68-91mcg. One ounce of brazil nuts (6-8 nuts) contains 544 mcg.
Rec: Don’t eat too many brazil nuts.
Submitted by: Donna Seger, MD
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Donna Seger, MD
Tennessee Poison Center
Poison Help Hotline: 1-800-222-1222