Selenium Toxicity, Brazil Nuts and Upper Limits

If someone may have taken too much

In the United States, call Poison Help at 1-800-222-1222 for anyone who may have swallowed a large amount of selenium or a supplement that may be mislabeled, and call 911 for severe symptoms. For other countries see Poison help by country. NIH ODS says acute selenium toxicity can cause severe stomach and nerve symptoms, breathing problems, kidney failure and, rarely, death. [1]

Short answer

Selenium is an essential trace mineral, and the gap between enough and too much is narrow. Too much selenium causes selenosis. Its mildest form is hair loss and nail changes. [2] [3] Amounts here are micrograms (mcg) of the element selenium. This page gives information only and is not dosing advice.

What selenosis looks like

MedlinePlus lists hair loss, nail problems, nausea, irritability, fatigue and mild nerve damage. [3] NIH ODS adds a garlic odor on the breath and a metallic taste as early signs, plus skin rash, diarrhea and nervous system abnormalities, and says organic and inorganic forms have similar effects with long-term high intake. [1] Symptoms alone cannot confirm selenosis, because many conditions cause hair and nail changes. A clinician decides what testing is needed.

Official upper limits

An upper limit (UL) is the highest daily intake unlikely to cause harm in most people of that group. It is not a target. Figures differ by body, and the sources below apply to selenium from food and supplements together, except where noted.

For comparison, the US recommended intake for adults is 55 mcg a day, 60 in pregnancy and 70 while breastfeeding (MedlinePlus, 2025 review). [3] The NHS gives 75 mcg for men and 60 mcg for women 19 to 64. [2] EFSA set its UL from hair loss seen at 330 mcg a day in the large SELECT trial, with a safety factor. [5] EFSA says toddlers and children should use selenium supplements with caution, based on individual needs. [5]

Brazil nuts

Brazil nuts are the richest food source. [1] NIH ODS gives an average of 544 mcg per ounce (6 to 8 nuts) and 68 to 91 mcg per nut, and says they could cause toxicity if eaten regularly. [1] That ounce is more than the 400 mcg US limit for adults, and NIH ODS notes other analyses vary widely. [1]

Why so much variation? A study of Amazon trees found median selenium from about 2 to 68 mg per kg of nuts depending on region, so one nut could supply from 11% to 288% of a 70 mcg adult daily requirement. Soil selenium and soil acidity both mattered. [6] EFSA says regular Brazil nut consumers and high-dose supplement users are the adults most likely to exceed its UL. [5]

Mislabeled supplements

In 2008, 201 people had severe reactions to a liquid supplement that contained 200 times the labeled amount of selenium. [1] A case series of nine patients found almost 200 times the reported amount on testing. Symptoms included hair loss, nail changes, stomach upset and memory difficulty. Blood selenium ranged 150 to 732 mcg/L, and none needed more than supportive care. [7] See Quality testing and certifications for what third-party testing can and cannot show.

Medicines and special groups

• Medicines: NIH ODS notes cisplatin, a chemotherapy medicine, can lower selenium levels, and cites a Cochrane review concluding the evidence that selenium supplements ease chemotherapy side effects is insufficient. [1] Tell your oncology team about every supplement, and see Medication interactions.
• Pregnancy and breastfeeding: ask a midwife or doctor first. See Pregnancy and breastfeeding.
• Kidney and liver disease, and before surgery: the sources we read did not set separate limits for these. Ask a clinician, and see Supplements before surgery.
• Testing: NIH ODS says plasma or serum selenium of 8 mcg/dL or higher is generally considered sufficient in healthy people and that hair and nail analysis is used to look at long-term intake. [1] Results need a clinician; ranges differ by lab.

Related pages

See Selenium for the full profile, Selenium and the thyroid for thyroid trials, and Mineral toxicity.