If your doctor mentioned selenium for an underactive thyroid, you are not alone. Let’s walk through how to use it wisely so you get the benefits without the pitfalls. We will follow one running example. Meet Maya, who just learned she has sluggish thyroid function and is thinking about selenium.

Why selenium matters for thyroid health

Selenium helps convert T4 to the active T3 hormone. Think of it like a reusable wrench in your thyroid’s toolbox. It is catalytic, not consumptive. That means the body recycles it during hormone conversion. Your thyroid is surprisingly good at conserving selenium, even when your intake is modest.

So selenium and thyroid health are connected. But more is not always better. This is where Maya needs a plan, not guesswork.

Safe selenium intake starts with food

Before supplements, reach for foods high in selenium. Great choices include Brazil nuts, shrimp, tuna, turkey, eggs, and whole grains. Many people hit their needs with diet alone.

A quick guide for Maya:

Most adults need about 55 micrograms per day. The upper limit is 400 micrograms per day. Stay well below this unless your clinician directs otherwise.Brazil nuts are potent. One to two nuts can meet or even overshoot daily needs depending on the nut and the soil it grew in. Eating a handful every day may push you into high intake over time.   

Simple swaps help. Maya adds two eggs at breakfast and shrimp or tuna at lunch once or twice a week. On days she wants Brazil nuts, she keeps it to one or two.

How to spot selenium toxicity symptoms

Early red flags can be subtle. A metallic taste in the mouth or garlic breath is often the first sign. Other early selenium toxicity symptoms include nausea, diarrhea, fatigue, irritability, muscle or joint pain, brittle or discolored nails, hair loss, skin rash, dizziness, and tremors.

Very high intake can lead to rare but serious issues like neurological problems, heart rhythm changes, liver injury, and even lower thyroid function. If Maya notices any of these after starting supplements