How many Brazil nuts before selenium toxicity?

January 8, 2026 •

3 min read

According to the National Institutes of Health, the tolerable upper intake level for selenium in adults is 400 micrograms per day. Knowing how many Brazil nuts before selenium toxicity occurs is crucial, as their selenium content is exceptionally high, making overconsumption a significant risk. Just a few nuts can push you over the safe daily limit, potentially causing selenosis with symptoms like hair loss and brittle nails.

Quick Summary

This guide explains the high selenium content in Brazil nuts and identifies the daily consumption limits to prevent toxicity. It details the symptoms of selenosis, outlines the benefits of moderate intake, and provides practical advice for safe consumption. Included is a comparison of Brazil nuts with other selenium sources.

Key Points

Daily Limit: Consume no more than one to two Brazil nuts per day occasionally to stay within safe selenium levels.
Risk of Selenosis: Eating 4-5 Brazil nuts daily can lead to chronic selenium toxicity with symptoms like hair loss and brittle nails.
High Potency: One Brazil nut can contain up to 91 mcg of selenium, exceeding the 55 mcg RDA for adults.
Watch for Symptoms: Early signs of excess selenium include a metallic taste and garlic breath.
Supplement Awareness: Combining Brazil nuts with selenium supplements increases toxicity risk.
Source Variation: Selenium content in Brazil nuts varies based on growing location.

Understanding the High Selenium Content of Brazil Nuts

Brazil nuts are known as the richest natural dietary source of selenium, an essential trace mineral. Selenium is important for thyroid function, the immune system, and protecting cells. However, the high concentration of selenium in these nuts can vary greatly based on where they are grown. A single Brazil nut typically contains between 68 and 91 micrograms (mcg) of selenium. This amount can be more than the recommended daily allowance (RDA) of 55 mcg for adults.

The Tipping Point: How Many Is Too Many?

The tolerable upper intake level (UL) for adults is 400 mcg per day. Due to their high selenium content, consuming too many Brazil nuts can quickly lead to exceeding this limit. A safe intake is generally considered to be one to three nuts consumed occasionally, not daily. Consistent daily consumption beyond this can result in selenosis, or selenium toxicity.

Acute vs. Chronic Selenium Toxicity

Selenium toxicity can be acute (sudden, large overdose) or chronic (long-term excessive intake). Acute toxicity is rare and more often linked to misformulated supplements. A notable incident involved a supplement with 200 times the labeled selenium. Chronic toxicity is more common with regular, high consumption of Brazil nuts. Eating just 4-5 nuts daily can put a person at risk of exceeding the 400 mcg daily limit.

Symptoms of Selenosis

Early signs of selenosis include a metallic taste and garlic-like breath. With continued high intake, symptoms can progress to gastrointestinal issues like nausea and diarrhea, fatigue, irritability, hair loss, brittle or discolored nails, skin problems, and nervous system issues. Very high doses can rarely lead to kidney failure, heart failure, and respiratory distress.

Comparison of Selenium Sources

The table below compares the selenium content of Brazil nuts to other common foods to highlight their exceptional potency.


Source	Average Selenium Content (per serving)	Daily Limit Concern	Notes
Brazil Nuts	~90 mcg per nut (can vary greatly)	Very High	Just 4-5 nuts can exceed the 400 mcg UL. Intake should be limited to 1-2 nuts occasionally.
Tuna (Canned)	~68 mcg per 3 oz (85g) serving	Low	Moderate intake is safe.
Shrimp	~40 mcg per 3 oz (85g) serving	Low	A good source that is less concentrated than Brazil nuts.
Chicken Breast	~22-35 mcg per 3 oz (85g) serving	Very Low	Provides a consistent and safe amount.
Eggs	~15 mcg per large egg	Very Low	A common food source with a moderate amount.

Practical Guidelines for Safe Consumption

To enjoy the benefits of Brazil nuts without the risk of selenium toxicity, consider these guidelines:

Portion Control: Limit consumption to one to two nuts occasionally, not every day.
Mix Nuts: Combine Brazil nuts with other nuts to vary nutrient intake and limit selenium.
Check Supplements: Be aware if your supplements contain selenium, as this adds to your total daily intake.
Origin Matters: Selenium levels vary based on where the nuts are grown.
Listen to Your Body: Reduce or stop consumption if you notice symptoms like metallic taste or garlic breath and consult a doctor.

Conclusion: The Final Word on Brazil Nuts

Brazil nuts are a potent source of selenium, essential for health. However, their high concentration means moderation is crucial to avoid selenosis. Limiting intake to one or two nuts occasionally can provide benefits without risks. Treat them as a supplement, not a regular snack. Consult a healthcare professional for personalized advice. For more information on selenium, visit the NIH Office of Dietary Supplements' fact sheet.

Frequently Asked Questions

Selenosis is selenium toxicity, resulting from high selenium levels in the body. Symptoms include hair loss, brittle nails, fatigue, and GI issues.

The adult tolerable upper intake level (UL) is 400 micrograms (mcg) per day from all sources. Consistently exceeding this level can cause toxicity.

Initial signs often include a metallic taste in the mouth and garlic-like breath.

One to two Brazil nuts per day occasionally can provide sufficient selenium for thyroid support without toxicity risk.

No, selenium content varies significantly based on soil composition where the nut was grown.

Due to high selenium, daily consumption is not recommended. One or two nuts a few times a week is a safer approach.

Acute toxicity is a rare, large overdose, often from supplements. Chronic toxicity results from consistent, long-term excessive intake, more likely from frequent, high Brazil nut consumption.