Introduction:

For years, Brazil nuts have been crowned the “natural selenium supplement” - a simple, food-based hack to support your thyroid, immune system, and fertility.
But here’s the catch: that claim is only half true.

In clinical practice, I often see women with thyroid disorders or autoimmune markers adding “two Brazil nuts a day” to their diet, expecting measurable improvement in selenium levels or thyroid antibodies. Yet, when we retest, there’s minimal change. Why? It often comes down to the soil. And why selenium beyond brazil nuts matters - but also whilst staying cautious of overdosing. 

The Science Behind Selenium

Selenium is a trace mineral essential for:

• Conversion of thyroid hormones (T4 > T3)

• Antioxidant activity (via glutathione peroxidase)

• Immune modulation and inflammation control

In autoimmune thyroid disease (Hashimoto’s, Graves’), selenium can play a protective role - reducing antibody activity, lowering oxidative stress, and supporting tissue repair.

Brazil Nuts: Nature’s Wild Card

Brazil nuts are often cited as one of the richest natural sources of selenium - but here’s what many people don’t realise:

• The selenium content of a single Brazil nut can vary from 0.03 µg to 512 µg per gram, depending on where it’s grown.

• This variation exists because the tree only absorbs what’s available in the soil.

• Some regions in Brazil and the Amazon are actually selenium-deficient, which means nuts grown there may offer little benefit.

In contrast, nuts grown in selenium-rich soils can contain dangerously high levels. So while one person’s “nut a day” might barely scratch the surface of their needs, another’s could easily tip into toxicity.

Why Soil Variability Matters in Clinical Practice

This is a prime example of why bio-individuality matters.
In functional medicine, we don’t just prescribe food lists - we assess absorption, nutrient status, and the environment those foods come from.

Selenium deficiency can show up as:

• Fatigue, hair loss, low mood

• Poor thyroid conversion (high TSH, low T3)

• Recurrent infections or autoimmune flare-ups

But overshooting your dose isn’t safe either - excessive selenium can cause nausea, brittle nails, and nervous system symptoms.

So, What’s the Solution?

• Test, don’t guess. A simple serum or plasma selenium test can confirm your baseline.

• Rotate sources. Include seafood, eggs, and high-quality supplements if needed.

• Don’t rely solely on Brazil nuts. They can be part of a nutrient-dense diet, but not your only selenium strategy.

• Work with a practitioner. Your thyroid, antibodies, and nutrient pathways all interact - getting this balance right takes clinical insight.

Final Thoughts

Your nutrition is only as good as the soil it comes from.
At InHer Health Clinic, we focus on precision nutrition - because for women managing autoimmune thyroid disease, every micronutrient counts.
If you’re tired of “food hacks” that don’t move the needle, it’s time to understand what your body actually needs - and where those nutrients really come from.

➡️ Explore our Hormone Rehab and Genetic Membership programs to start uncovering your unique nutrient blueprint. https://www.inherhealthclinic.com/memberships