Brazil Nuts and Your Thyroid: How Many per Day, and Is It Safe?

A single Brazil nut usually covers a full day's selenium, and a handful of them goes past the safe daily limit. That makes Brazil nuts one of the easiest ways to get enough selenium for your thyroid, and also the easiest food to overdo.

How much selenium is in one Brazil nut, and why does it vary so much?

The NIH Office of Dietary Supplements (ODS) puts one Brazil nut at 68–91 µg of selenium, and a 1-ounce serving (6–8 nuts) at an average of 544 µg [C1]. The adult Recommended Dietary Allowance (RDA) is 55 µg a day, so one nut alone is more than 100% of it [C1]. USDA's food database lists Brazil nuts at 1,917 µg per 100 g, with one kernel weighing about 5 g, which works out to roughly 96 µg for an average nut [C2].

Those are averages, and individual nuts swing far more. The selenium in plant foods depends on how much selenium is in the soil and on soil conditions such as pH, so the same food can differ widely by where it grew [C1]. A study of Brazil nuts and the soil under the trees across the Brazilian Amazon found median selenium levels ranging from 2.07 mg/kg in Mato Grosso to 68.15 mg/kg in Amazonas [C5]. Depending on origin, one nut could supply anywhere from 11% to 288% of an adult man's daily need, with more selenium in the nuts where the soil held more selenium and less where the soil was acidic [C5].

In a New Zealand trial, two nuts a day were expected to provide about 100 µg, but the nuts actually supplied an average of 53 µg a day, with a possible range of 20–84 µg [C3]. The package does not tell you where your nuts grew, so the practical move is to plan around the higher figure.

Brazil nuts vs. other selenium-rich foods

Brazil nuts are in a league of their own, but they are not the only source. Seafood, meat, poultry, and organ meats are the next-richest foods, and breads, grains, meat, poultry, seafood, and eggs supply most of the selenium in the US diet [C1]. Every value below comes from the ODS selenium fact sheet table, which uses the 55 µg Daily Value (the same number as the adult RDA) [C1].

Food	Typical serving	Selenium (µg)	% of the 55 µg RDA
Brazil nut	1 nut	68–91	124–165%
Brazil nuts	1 oz (6–8 nuts)	544	989%
Tuna, yellowfin, cooked	3 oz	92	167%
Sardines, canned in oil, with bone	3 oz	45	82%
Shrimp, cooked	3 oz	42	76%
Chicken, light meat, roasted	3 oz	22	40%
Cottage cheese, 1% milkfat	1 cup	20	36%
Egg, hard-boiled	1 large	15	27%
Brown rice, long-grain, cooked	1 cup	12	22%
Whole-wheat bread	1 slice	8	15%
Yogurt, plain, low fat	1 cup	8	15%

Source: NIH ODS Selenium Fact Sheet, Table 2 [C1]; the per-nut figure is from the same fact sheet's text. Percentages for one nut are calculated from 55 µg.

Most people already get enough without trying. Average US intake from food and drinks is 108 µg a day, about 94 µg for adult women and 132 µg for adult men [C1]. For how selenium fits with zinc, iron, vitamin D and B12 on a plate, see thyroid meals built around these nutrients.

How many Brazil nuts per day is safe?

The Tolerable Upper Intake Level (UL) for adults is 400 µg of selenium a day, from food and supplements combined [C1]. It was set from the intakes linked to hair and nail problems [C1]. ODS notes that because Brazil nuts are so concentrated, they could cause selenium toxicity if eaten regularly [C1].

How many Brazil nuts	Approx. selenium (µg)	vs. the 400 µg/day upper limit
1 nut	68–91	17–23%
2 nuts	136–182	34–46%
3 nuts	204–273	51–68%
4 nuts	272–364	68–91%
5 nuts	340–455	85–114%
1 oz (6–8 nuts)	about 544	about 136%

Calculated from the ODS figures of 68–91 µg per nut and 544 µg per ounce [C1]. Individual nuts can be much higher or lower [C5].

Remember that the nuts sit on top of everything else you eat. Add the 94–132 µg a typical US diet already supplies [C1], and from about 4 nuts a day upward your total can pass 400 µg. One or two nuts, on some days rather than as a daily handful, gives you a full day's selenium with a wide safety margin. If you like them as a snack, a two-nut portion such as Brazil nuts with dried apricots keeps the amount clear.

Do Brazil nuts work as well as a selenium supplement?

For raising selenium levels, yes. In a 12-week randomized trial in 59 New Zealand adults, Thomson and colleagues compared 2 Brazil nuts a day, 100 µg of selenium as selenomethionine, and placebo [C3]. Plasma selenium rose by 64.2% with the nuts, 61.0% with the supplement, and 7.6% with placebo [C3]. Whole-blood glutathione peroxidase, a selenium enzyme, rose more with the nuts (13.2%) than with the supplement (5.3%) [C3].

A 2025 German trial in 86 adults (44 vegans, 42 omnivores) gave an extra 55 µg of selenium a day for two weeks, either as Brazil nut butter or as a supplement [C4]. Both raised serum selenium and selenoprotein P equally, and the authors concluded that Brazil nuts can improve selenium status when eaten once in a while [C4]. Both trials measured selenium status, not thyroid outcomes, and unlike a tablet a nut has no labeled dose, as the New Zealand trial showed [C3].

What does selenium do in the thyroid?

The thyroid holds more selenium per gram than any other organ in the body [C1]. The three deiodinase enzymes that switch the storage hormone T4 into active T3 are built around selenocysteine, a selenium-containing amino acid [C6]. If you take levothyroxine, these are the enzymes that turn your T4 tablet into T3; our guide to deiodinases explains that step in more detail.

Selenium enzymes also protect the gland. Glutathione peroxidases and thioredoxin reductase help clear the hydrogen peroxide the thyroid produces while making hormone [C1]. The body also prioritizes the thyroid: during selenium deficiency, the gland keeps its selenium and its deiodinase levels close to normal [C6]. Iodine is the thyroid's other key mineral, and there too more is not better (iodine and hypothyroidism).

Do Brazil nuts help Hashimoto's?

No trial in this evidence base tested Brazil nuts in Hashimoto's; the studies used selenium supplements. The largest recent meta-analysis pooled 35 randomized trials and found that selenium lowered TPO antibodies (29 groups, 2,358 participants) and slightly lowered TSH in people not taking thyroid hormone [C7]. Free T4 and free T3 did not change significantly [C7]. Many participants started with deficient or marginal selenium status, and ODS notes that more research is needed, including by selenium status [C1].

Lower antibodies have not translated into feeling better. In the 12-month CATALYST trial, 412 people with autoimmune thyroiditis taking levothyroxine got 200 µg of selenium a day or placebo, and quality of life improved equally in both groups [C8]. The American Thyroid Association recommends against selenium supplements for TPO-antibody-positive pregnant women [C9][C1]. Nothing here is a reason to change your levothyroxine dose; that stays with your doctor. Our selenium and Hashimoto's article covers the supplement trials in full.

What are the signs of too much selenium?

Chronic excess, called selenosis, most often shows up as hair loss and brittle or lost nails [C1]. Early clues are garlic-smelling breath and a metallic taste in the mouth; skin rash, nausea, diarrhea, fatigue, irritability, and nervous system problems can follow [C1]. In 2008, 201 people had severe reactions to a liquid supplement that contained 200 times the selenium on its label; severe acute poisonings like this have come from misformulated products [C1].

The realistic risk with Brazil nuts is stacking. Many multivitamins contain 55 µg of selenium, combination products often 50–200 µg, and selenium-only supplements 100–400 µg [C1]. A 200 µg supplement plus 2 nuts (136–182 µg) plus an ordinary diet (94–132 µg) adds up to about 430–514 µg, over the 400 µg limit [C1]. If you take any supplement with selenium in it, read the label before adding nuts.

When to talk to your doctor

Ask your doctor, endocrinologist, or pharmacist before eating Brazil nuts regularly if:

• you already take a selenium supplement, a "thyroid support" blend, or a multivitamin with selenium;
• you are pregnant or breastfeeding (the RDA is 60 µg and 70 µg) or planning pregnancy with positive TPO antibodies [C1][C9];
• you are on kidney dialysis, where selenium status varies a lot from person to person [C1];
• you are thinking of giving them to a child, since the upper limit is 90 µg at ages 1–3, 150 µg at 4–8, and 280 µg at 9–13 [C1];
• you notice hair shedding, brittle nails, or garlic breath and eat Brazil nuts or take selenium.

Bring your full supplement list to the visit. In Thyra, the "Can I eat this?" food check gives you a quick read on a food like Brazil nuts before you add it to your routine, and the Hashimoto's food list puts it next to other thyroid-relevant foods.

Frequently asked questions

How many Brazil nuts should I eat a day for my thyroid?

One or two nuts give most adults a full day's selenium (68–91 µg per nut against a 55 µg RDA) [C1]. You do not need them daily if you eat fish, eggs, or meat, and a regular 1-ounce handful (about 544 µg) exceeds the 400 µg/day limit [C1].

Is it safe to eat Brazil nuts if I take levothyroxine?

There is no known direct interaction, and the CATALYST trial gave 200 µg of selenium a day alongside levothyroxine for 12 months [C8]. As with any food eaten close to your tablet, keep your usual gap around your dose, and ask your pharmacist if you are unsure.

Can I eat Brazil nuts and take a selenium supplement?

Usually that means too much. A 200 µg supplement, 2 nuts, and a normal diet can add up to 430–514 µg a day, over the 400 µg limit [C1]. Pick one source, and decide with your doctor whether a supplement is needed at all.

Do Brazil nuts lower TPO antibodies?

There are no Hashimoto's trials of Brazil nuts. Selenium supplements lowered TPO antibodies in a meta-analysis of 35 trials [C7], but a 12-month trial found no quality-of-life benefit over placebo [C8].

What are the best selenium foods besides Brazil nuts?

Per the NIH table, 3 oz of yellowfin tuna has 92 µg, sardines 45 µg, shrimp 42 µg, roasted chicken 22 µg, and one egg 15 µg [C1]. Cottage cheese, brown rice, and whole-wheat bread add smaller amounts [C1].

Bottom line

One or two Brazil nuts on some days give you a full day's selenium; a daily handful pushes you past the 400 µg upper limit. If you take a multivitamin or a selenium supplement, count it before adding nuts. For Hashimoto's, selenium may lower antibodies but has not been shown to make people feel better, so bring the supplement question to your doctor.