Brazil Nuts and Selenium: How Many Should You Eat a Day?

Brazil nuts are the richest known food source of selenium, a trace mineral the body needs in very small amounts. That is good news if you want to get selenium from food rather than a tablet, but it also means more is not better. A couple of Brazil nuts can do the job. A whole bag in a week is a different story.

Here is what the science says about selenium, how much is actually in a Brazil nut, and how many you need.

What is selenium and why do we need it?

Selenium is an essential mineral. We can't make it, so it has to come from what we eat. The body uses it to build a group of proteins called selenoproteins, including glutathione peroxidase, an enzyme that forms part of our natural antioxidant defences.

In the UK, food businesses can only describe the role of a nutrient using wording that has been approved after scientific review. For selenium, the approved statements are:

• Selenium contributes to the normal function of the immune system.
• Selenium contributes to normal thyroid function.
• Selenium contributes to the protection of cells from oxidative stress.
• Selenium contributes to the maintenance of normal hair and normal nails.
• Selenium contributes to normal spermatogenesis.

Plenty of websites go further than this. We don't, because these are the claims the evidence supports.

How much selenium do you need?

The UK reference nutrient intake for adults is 75 micrograms (µg) a day for men and 60 µg a day for women. A microgram is a thousandth of a milligram, so we are talking about a tiny amount.

Even so, many people in the UK fall short. A 2018 analysis of the National Diet and Nutrition Survey found that 50.3% of women and 25.8% of men had selenium intakes from food below the lower reference nutrient intake, the level below which intake is likely to be inadequate for most people. Part of the reason is geography. The selenium in plant foods depends on the soil they were grown in, and soils in the UK and much of Europe are relatively low in it.

How much selenium is in a Brazil nut?

There is no single answer, and the reason lies in the soil.

Brazil nut trees grow wild in the Amazon rainforest, and the amount of selenium they take up depends on where they grow. A 2017 study published in Chemosphere sampled nuts and soil across five Brazilian states. It found that selenium in the nuts rose with the selenium content of the soil but fell in more acidic soils. Depending on origin, the researchers calculated that a single nut could provide anywhere from 11% to 288% of an adult man's daily requirement.

The variation doesn't stop at region. Earlier work that tested 162 individual nuts from each of two regions found big differences between nuts from the same area, and even between trees. So any figure you see quoted for "selenium per Brazil nut" is an average, not a guarantee.

Do Brazil nuts actually raise selenium levels?

Yes, and this has been tested directly. In a 12-week randomised controlled trial at the University of Otago, 59 adults in New Zealand, where soil selenium is also low, were given either two Brazil nuts a day, a 100 µg selenium supplement (as selenomethionine) or a placebo.

Plasma selenium went up by 64.2% in the Brazil nut group, 61.0% in the supplement group and 7.6% in the placebo group. The two Brazil nuts turned out to provide an average of 53 µg of selenium a day, about half of what the researchers expected, yet they raised selenium levels as effectively as the supplement. Activity of glutathione peroxidase also increased. The authors concluded that two Brazil nuts a day were as effective as the 100 µg supplement for improving selenium status.

Can you eat too many Brazil nuts?

You can. Selenium is one of those nutrients where the gap between enough and too much is fairly narrow.

In 2023 the European Food Safety Authority (EFSA) reviewed the evidence and set a tolerable upper intake level of 255 µg a day for adults, from all sources combined. Hair loss was chosen as the critical effect, as it is one of the earliest signs of long-term excess intake. Brittle nails are another. EFSA noted that most adults are unlikely to go over the upper level, with two exceptions: people regularly taking high-dose selenium supplements, and regular consumers of Brazil nuts.

Because the selenium content of each nut varies so much, it makes sense to keep portions small:

• One to three Brazil nuts a day is plenty for most adults.
• Don't eat them by the handful every day.
• If you already take a multivitamin or a hair, skin and nail supplement, check the label. Many contain selenium, and it all adds up.
• Whole nuts aren't suitable for children under five because of the choking risk.

Easy ways to eat your daily Brazil nut

With a portion this small, it's easy to fit Brazil nuts into the day:

• Eat one or two on their own with a piece of fruit.
• Chop and scatter over porridge, yoghurt or a smoothie bowl.
• Stir into homemade granola, flapjacks or energy balls (and share them out across the week).
• Blend a few into pesto in place of pine nuts.
• Grate finely over salads or roasted vegetables.

If you're baking or blending, organic broken Brazil nuts are the same nut in pieces and save you the chopping.

Our organic Brazil nuts

Our Organic Brazil Nuts are large, raw, certified organic kernels, wild-harvested from rainforest trees in Bolivia, Brazil and Peru. Nothing is added: no salt, no oil, no sugar. Keep them in a cool, dry place in a sealed pouch or jar, as their high oil content means they're best eaten fresh.

A bag lasts a long time when you only need a nut or two a day.

Sources

• Thomson CD et al. (2008). Brazil nuts: an effective way to improve selenium status. American Journal of Clinical Nutrition 87(2): 379–384. PubMed
• EFSA Panel on Nutrition, Novel Foods and Food Allergens (2023). Scientific opinion on the tolerable upper intake level for selenium. EFSA Journal 21(1): e07704. doi:10.2903/j.efsa.2023.7704
• Silva Junior EC et al. (2017). Natural variation of selenium in Brazil nuts and soils from the Amazon region. Chemosphere 188: 650–658. doi:10.1016/j.chemosphere.2017.08.158
• Chang JC et al. (1995). Selenium content of Brazil nuts from two geographic locations in Brazil. Chemosphere 30(4): 801–802.
• Derbyshire E (2018). Micronutrient intakes of British adults across mid-life: a secondary analysis of the UK National Diet and Nutrition Survey. Frontiers in Nutrition 5: 55. doi:10.3389/fnut.2018.00055
• British Nutrition Foundation. Selenium and health: summary. nutrition.org.uk
• Great Britain nutrition and health claims (NHC) register. GOV.UK