The Selenium in Brazil Nuts and What It Does to Testosterone

Brazil nuts are particularly high in selenium. In a randomized trial, eating two a day raised selenium status as effectively as taking a supplement. The evidence on testosterone is narrower: the one trial that measured testosterone in men involved 468 infertile men who received supplemental selenium, and the strongest arm also included N-acetyl-cysteine. Two Brazil nuts averaged 53 mcg of selenium, compared with the 400 mcg adult ceiling published by the National Institutes of Health. To know where your own testosterone sits, you need to have it measured.

Selenium in Brazil Nuts

Selenium is a mineral used to make 25 selenoproteins, including glutathione peroxidases, thioredoxin reductases, and selenoprotein P. These proteins support thyroid hormone metabolism, DNA synthesis, reproduction, and protection from oxidative damage.¹

The National Institutes of Health Office of Dietary Supplements identifies Brazil nuts as a concentrated food source of selenium. Selenium levels in plant foods depend on the soil, geographic location, and other growing conditions.¹ That variability makes Brazil nuts different from foods with a more predictable nutrient profile.

Selenium supports biological processes involved in reproduction. That mechanism does not establish that more selenium will raise your testosterone. Most people in the United States already consume adequate selenium, and the available trials do not establish Brazil nuts as a treatment for low testosterone.¹

Counting nuts leaves the hormone unmeasured. Your testosterone result, related biomarkers, and symptoms give a physician the context a fixed nut count cannot provide.

Daily Brazil Nut Amounts in Human Trials

Published trials have studied daily amounts of one or two Brazil nuts, but the selenium content was not consistent between nuts.

In a randomized trial of 59 New Zealand adults, Thomson et al. assigned participants to two Brazil nuts, supplemental selenomethionine, or placebo each day for 12 weeks. Researchers expected the two nuts to provide about 100 mcg of selenium. The measured average was 53 mcg, with a possible range of 20 to 84 mcg.²

The two-nut group increased plasma selenium by 64.2% and increased glutathione peroxidase activity. The trial measured selenium status and antioxidant activity. It did not measure testosterone or other hormones.²

Published Evidence	Daily Amount Studied	What Researchers Measured
Thomson et al. trial	Two Brazil nuts	Selenium status and glutathione peroxidase activity
Expected selenium content	About 100 mcg	Estimate before testing
Actual selenium content	53 mcg average	Possible range of 20 to 84 mcg

The 20 to 84 mcg spread came from the trial population. It does not measure your individual intake. A fixed daily nut count treats a variable food as a one-size plan.

The answer to how many Brazil nuts per day are safe cannot come from nut count alone. The same count can produce a different selenium intake. Your total exposure also depends on other foods and any supplements containing selenium.

A Safe Selenium Ceiling for Daily Intake

The Food and Nutrition Board sets selenium intake values of 55 to 70 mcg for adults, depending on life stage. This is a range across adult groups. It is not a single target for every adult.¹

The adult Tolerable Upper Intake Level is 400 mcg per day.¹ This figure is a ceiling for chronic intake. It is not a recommended dose, and it does not mark the exact intake at which symptoms begin.

Chronically high intake can cause selenosis, which is selenium toxicity. The National Institutes of Health lists hair loss, brittle or lost nails, garlic odor on the breath, metallic taste, skin rash, nausea, diarrhea, fatigue, irritability, and nervous system abnormalities as possible signs.¹

If you ate 10 Brazil nuts on one occasion, that event does not establish selenosis. The condition described by the National Institutes of Health follows chronically high selenium intake.¹ Ten nuts also cannot be assigned a reliable selenium dose because selenium content varies so widely.

If you have been eating a handful every day, bring the approximate nut count, duration, supplement labels, and any symptoms to a clinician. Those details allow your clinician to assess total exposure instead of guessing from the number of nuts.

Human Trial Evidence for Male Hormones

The male testosterone evidence comes from one trial of selenium supplements in infertile men. It does not show that Brazil nuts raise testosterone in healthy men.

Safarinejad et al. studied 468 men with idiopathic oligo-asthenoteratospermia, a form of male infertility involving abnormal sperm count, movement, and shape. Participants received 200 mcg of supplemental selenium daily, N-acetyl-cysteine, both compounds, or placebo for 26 weeks, followed by a 30-week treatment-free period. That daily amount is close to four times the 53 mcg the two Brazil nuts delivered in the Thomson trial, so the study does not describe what eating nuts does to your hormones.³

Serum testosterone increased in response to selenium and N-acetyl-cysteine treatment. The abstract did not report the size of that increase, and the combined treatment produced the strongest effects.³ This makes it difficult to isolate selenium as the cause.

The population also limits the conclusion. These participants had diagnosed infertility. They were not healthy men eating Brazil nuts, and they were not selected for low testosterone. Because that trial does not describe a healthy man eating nuts, the direct answer for you is your own total and free testosterone, measured and read against your symptoms.

Population-Specific Testosterone Findings

Selenium has not changed testosterone in the same direction across all populations.

Rashidi et al. conducted a randomized, double-blind, placebo-controlled trial in 66 women with polycystic ovary syndrome (PCOS). The participants were women aged 18 to 45, a starting hormonal state that has nothing in common with yours. After 12 weeks of selenium supplementation, serum testosterone declined in the intervention group compared with placebo.⁴

This trial does not predict how selenium affects men. It does show why selenium cannot be described as a one-directional testosterone enhancer. Starting hormone levels, sex, health status, and the intervention studied can change the result.

Measured Benefits of Brazil Nuts

Human Brazil nut trials have focused mainly on selenium status, antioxidant activity, lipids, and glucose.

A 2022 systematic review by da Silva et al. included 24 studies of Brazil nut consumption. Fifteen were non-randomized. Every study that assessed antioxidant status reported increased selenium, glutathione peroxidase activity, or both. The review also reported improvements in lipid markers and fasting glucose among healthy participants.⁵

The review reported no testosterone finding. Brazil nuts may improve selenium-related biomarkers, but that evidence cannot be converted into a claim that you will produce more testosterone.

A 2025 randomized trial by Simon et al. also found that Brazil nut butter and a selenium supplement were equally effective at raising serum selenium and selenoprotein P over two weeks. The trial included vegans and omnivores and measured no hormones.⁶

A separate trial by Moriguchi Watanabe et al. studied one Brazil nut daily for three months in 32 statin users.⁷ Thomson used two nuts a day and Moriguchi Watanabe used one, which is the whole range of daily amounts these trials put to the test. What that adds to your own selenium intake depends on the rest of your diet and any supplements, which your physician can review with you.

A Physician-Led Testosterone Assessment

Your testosterone level requires a blood test. Brazil nuts cannot tell you whether your level is low, whether free testosterone is reduced, or whether your symptoms come from another cause.

The intake range and upper limit above are population figures. They do not show your selenium status or testosterone level. Your physician needs your measurements and symptoms to interpret what those numbers mean for you.

If you are concerned about energy, libido, muscle loss, or body composition, start by learning where to get your testosterone tested. A physician can interpret your result with your symptoms and related biomarkers. One testosterone value provides limited context. A pattern across hormones, thyroid function, metabolic markers, sleep, medications, and symptoms gives your physician more information to act on.

Selenium has a defined place in nutrition, and deficiency deserves clinical attention. It should not replace an evaluation for low testosterone. You can read more about selenium and other testosterone supplements without treating a supplement label as a hormone plan.

If your testosterone is confirmed low and you have related symptoms, your physician may discuss underlying causes and treatment options. Testosterone replacement therapy is one possible option, but it is not automatic.

The Opt Take on Brazil Nuts and Testosterone

A food question about testosterone cannot be answered without a measurement. At Opt Health, the answer starts with a panel of 55+ biomarkers and a physician who reads the results against your symptoms, health history, medications, sleep, nutrition, and goals. The physician builds your plan from that pattern.

The underlying driver may involve hormones, thyroid function, insulin, sleep, or a nutrient gap. A fixed nut count cannot separate those possibilities or confirm low testosterone.

The first blood draw sets your baseline. Labs and a physician consultation repeat every three to four months. Repeat testing shows whether your numbers changed and gives the physician a basis for adjustment.

Get started: Begin with Opt Health, where a physician reads your labs, builds your plan, and adjusts it over the loop.

Frequently Asked Questions

This content is for informational purposes and does not replace evaluation, diagnosis, or treatment by a qualified medical professional.