Most foods give you a little selenium. Brazil nuts give you a lot. A single nut can contain more selenium than an adult needs in a whole day, which makes them one of the most efficient foods in the world for one nutrient, and one of the few where eating too many is a real concern.
We looked at the research on Brazil nuts and selenium: what selenium does, how well the nuts work compared with a supplement, whether selenium prevents disease, and how many is too many. Short version: one or two Brazil nuts a day is an excellent, cheap way to cover your selenium needs. A handful every day is not a good idea.
Brazil nuts at a glance: how strong is the evidence?
- 🥜 Raising selenium levelsStrong, controlled trial vs supplement
- ❤️ CholesterolOne tiny study, interesting but unproven
- 🎗️ Preventing prostate cancer with seleniumLarge trial found no benefit
- ⚠️ Too much seleniumReal risk with large daily amounts
- 📏 Sensible amountOne to two nuts a day
🧪 What selenium does
Selenium is a trace mineral your body builds into about two dozen proteins called selenoproteins. Some are antioxidant enzymes, such as glutathione peroxidase, that protect cells from damage. Others are needed to activate thyroid hormone, support the immune system and make healthy sperm.
Adults need 55 micrograms (mcg) a day, according to the NIH’s Office of Dietary Supplements, and 60 to 70 mcg in pregnancy and breastfeeding. Most Americans get enough from bread, meat, fish and eggs, but intake varies widely around the world depending on how much selenium is in the soil.
🥜 How much selenium is in a Brazil nut?
Brazil nuts grow wild in the Amazon rainforest, and the trees pull selenium up from the soil. The NIH lists a one-ounce serving, about six to eight nuts, at roughly 544 mcg of selenium. That works out to around 70 to 90 mcg per nut on average, but the real number varies enormously from nut to nut and from region to region. Some nuts contain far more, some far less.
📊 Two nuts versus a supplement: the trial
In a 2008 study in the American Journal of Clinical Nutrition, researchers in New Zealand, a country with low-selenium soil, randomly assigned 59 adults to eat two Brazil nuts a day, take a 100 mcg selenium supplement, or take a placebo for 12 weeks.
Two Brazil nuts a day raised blood selenium and the activity of the antioxidant enzyme glutathione peroxidase just as effectively as the supplement. The researchers concluded that eating Brazil nuts is an effective way to improve selenium status and could be used instead of supplements.
❤️ What about cholesterol?
A 2013 study in the Journal of Nutrition and Metabolism gave 10 healthy volunteers a single serving of 0, 5, 20 or 50 grams of Brazil nuts and followed them for 30 days. After the larger servings, LDL (“bad”) cholesterol went down and HDL (“good”) cholesterol went up, and the effect lasted for weeks. That is an interesting result, but with only 10 people it is a starting point, not proof. Nuts in general are linked with better heart health in large population studies, so Brazil nuts fit well into a heart-friendly diet either way.
🎗️ Does selenium prevent cancer?
Early studies suggested that people with more selenium had less cancer, which led to one of the largest prevention trials ever run. The SELECT trial, published in JAMA in 2009, gave more than 35,000 men 200 mcg of selenium a day, vitamin E, both, or a placebo. Selenium did not prevent prostate cancer or any other cancer, and the trial was stopped early. There was also a small, non-significant rise in diabetes in the selenium group.
Our read: getting enough selenium matters. Getting extra, beyond what you need, has not been shown to help and may carry risks.
⚠️ How many Brazil nuts is too many?
The safe upper limit for adults is 400 mcg of selenium a day from all sources. Eat a full ounce of Brazil nuts daily and you can be well above that, before counting the selenium in the rest of your diet.
Too much selenium over time causes a condition called selenosis. Early signs include a garlic smell on the breath, a metallic taste, brittle or lost hair and nails, skin rashes, fatigue and irritability. Very high intakes can affect the nerves.
- For daily eating: one or two nuts a day is plenty.
- For snacking: a larger handful now and then is fine, just not every day.
- If you take a multivitamin or selenium supplement: check its selenium content, and consider skipping the supplement if you eat Brazil nuts daily.
- For kids: their upper limit is much lower, so half a nut to one nut is enough.
🦋 Selenium and the thyroid
The thyroid contains more selenium per gram than any other organ, and selenium is needed to convert thyroid hormone into its active form. Some trials have tested selenium in autoimmune thyroid disease (Hashimoto’s), with mixed results, mostly showing lower antibody levels rather than clear changes in how people feel. If you have a thyroid condition, ask your doctor before adding Brazil nuts every day, so they can factor it in.
🛒 What to look for when buying
- Fresh, not rancid. Brazil nuts are high in fat and can go stale quickly. Store them in the fridge or freezer.
- Raw or lightly processed. Soaked and dried nuts are easier for some people to digest and have a crisper texture.
- Organic if you can. Most Brazil nuts are wild-harvested, but organic certification adds a layer of oversight on handling.
- Buy what you will finish. At two a day, a pound lasts a long time.
Where we buy Brazil nuts
Wildly Organic sells certified organic Brazil nuts that are raw, soaked and dried. Keep them in the freezer, and stick to one or two a day.
Affiliate link. We may earn a commission if you buy, at no extra cost to you. Price and availability are set by the retailer and can change.
Frequently asked questions
Can I eat Brazil nuts every day?
Yes, one or two a day is a sensible amount for most adults. It is daily handfuls that can push selenium too high.
Do Brazil nuts help with hair growth?
Selenium deficiency can affect hair, but extra selenium does not grow more hair. In fact, too much selenium causes hair loss.
Are Brazil nuts radioactive?
They contain tiny amounts of naturally occurring radium, picked up from the soil. At normal portions, the amount is not considered a health concern.
The honest bottom line
Brazil nuts are the most concentrated food source of selenium, and two a day raised selenium levels as well as a supplement in a controlled trial. Extra selenium beyond what you need has not been shown to prevent cancer, and daily handfuls can push you past the safe limit. Treat Brazil nuts like a natural supplement: one or two a day, kept fresh in the fridge.
Studies and sources
- Thomson CD et al. (2008). Brazil nuts: an effective way to improve selenium status. American Journal of Clinical Nutrition, via PubMed.
- Colpo E et al. (2013). A single consumption of high amounts of the Brazil nuts improves lipid profile of healthy volunteers. Journal of Nutrition and Metabolism, via PubMed.
- Lippman SM et al. (2009). Effect of selenium and vitamin E on risk of prostate cancer and other cancers: the SELECT trial. JAMA, via PubMed.
- Selenium: fact sheet for health professionals. NIH Office of Dietary Supplements.
This article is for general education and is not medical advice. Talk to your doctor or pharmacist before starting a supplement, especially if you take medication or have a health condition. These statements have not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure, or prevent any disease.
