The Minerals, and the Brazil Nut Ceiling

Selenium has the strongest evidence of any mineral in autoimmune thyroid disease. A meta-analysis of 21 studies covering 1,610 people found thyroid antibodies fell at three and six months, usually at 200 micrograms a day. Brazil nuts reach that dose easily, which is the problem. Two or three is a serving. A handful is too much.

the fourth of eight letters about solving my own thyroid. the first one is here. please read the note at the bottom.

The cupboard that got out of hand

There was a period when my kitchen shelf looked like a small pharmacy. Selenium, magnesium, zinc, a bag of brazil nuts the size of a pillow, and pumpkin seeds I roasted every Sunday with the devotion of someone performing a ritual. I knew minerals mattered for the thyroid. I did not know how much.

What does selenium do for the thyroid?

Selenium is the one mineral here with good human data. The thyroid holds more selenium per gram than any other organ, and needs it to make the enzymes that convert T4 into the active T3 your tissues use. The evidence that matters is a meta-analysis of 21 studies, 1,610 participants, which found selenium significantly reduced thyroid peroxidase antibodies at three and six months, at a dose across most trials of 200 micrograms a day.

Now the honest part. Falling antibodies are not the same thing as feeling better. What you and I care about is getting through four o'clock without lying down, and the trials measured the number far more reliably than they measured the woman.

How many brazil nuts a day is safe?

This is the part I would tear out and pin to the cupboard door. One brazil nut contains 68 to 91 micrograms of selenium, depending on the soil it grew in. The adult requirement is 55 micrograms, and the upper tolerable limit is 400 micrograms a day.

• One nut: 68 to 91 micrograms. Already above the daily requirement.
• Two to three nuts: 140 to 270 micrograms. The range the trials used.
• Four to five nuts: 270 to 455 micrograms. At or past the daily limit.
• A handful of eight: 550 to 730 micrograms. Well past it, without noticing.

Too much selenium over time is called selenosis. Brittle nails, hair that comes away, a metallic taste, garlic on the breath when you have eaten none. Hair loss and fatigue are also what an untreated thyroid does, so a woman can overdose on the thing she took to help and read it as proof she needs more.

I keep brazil nuts in a small jar now, not a bag. Three in the morning, and no capsule the same day. If you already supplement, the nuts count toward the total.

Does magnesium help hypothyroidism?

Here I step down a tier and say so plainly. For the thyroid specifically, magnesium is associational at best. Observational findings link low magnesium with thyroid antibodies, and the trial evidence selenium has is simply not there. Anyone telling you magnesium fixes a thyroid is ahead of the data. What I will say is what it does for me, which is sleep, and given that the last letter was about resting properly, that is not a small thing.

The pumpkin seeds belong here as one of the better food sources of magnesium and zinc, and that is the whole claim I make for them. You will find writing online presenting them as a parasite cleanse with the thyroid attached. I leave that out deliberately, because routine cleansing without a diagnosed infection has no good evidence base.

Should you take iodine for hypothyroidism?

Not on your own reading, mine included. Iodine is the raw material the thyroid builds hormone from, so the logic that more must be better is easy to follow and wrong. Where a diet is already iodine-sufficient, true across most of North America and Europe because of iodised salt, extra iodine can make autoimmune thyroid disease worse. Kelp is the least predictable route in, its content varying enormously between batches. A question for a doctor.

What is on my shelf now

Smaller than it was, the through-line of this series. I am a designer and a Kundalini Yoga teacher in Bali, not a clinician.

• Selenium, three brazil nuts in the morning, or a capsule, never both
• Magnesium in the evening, for sleep, named honestly as that
• Roasted pumpkin seeds, as food, for magnesium and zinc
• No iodine and no kelp unless a doctor puts them there
• Ferritin, vitamin D and B12 measured rather than guessed at, which was the second letter

None of it replaced my medication. None of it was ever going to.

Frequently asked questions

Does selenium help Hashimoto's?

The best evidence is a meta-analysis of 21 studies with 1,610 participants, which found selenium significantly reduced thyroid peroxidase antibodies at three and six months, typically at 200 micrograms a day. Falling antibodies are not the same as feeling better, and that part is far less settled.

How many brazil nuts a day for selenium?

Two or three a day is the sensible ceiling for most adults. One nut carries 68 to 91 micrograms depending on soil, the adult requirement is 55 micrograms, and the upper tolerable limit is 400 micrograms a day. A handful of eight can pass that limit alone, and any capsule counts toward the same total.

Can you take too much selenium?

Yes. Sustained intake above the 400 microgram upper limit can cause selenosis, whose signs include brittle nails, hair loss, a metallic taste and a garlic odour on the breath. Because hair loss and fatigue also occur with an underactive thyroid, too much selenium is easily mistaken for too little.

Is magnesium good for the thyroid?

For thyroid function specifically the evidence is associational rather than proven. Observational studies link low magnesium with thyroid antibodies, but there is no trial base comparable to selenium. Magnesium is reasonable for sleep, which matters when fatigue is the main symptom.

Should I take iodine if I have hypothyroidism?

Not without medical advice. Where dietary iodine is already sufficient, as across most of North America and Europe because of iodised salt, extra iodine from high-dose supplements or kelp can worsen autoimmune thyroid disease rather than improve it.

Next letter, black seed oil and castor oil. One has a small randomised trial. The other I use nightly and cannot claim a thing for.

With love from Bali,
Myrah