Know what you're putting in your body.

158 herbs, nutrients, and compounds. What the science says, what tradition knew, and what to watch for. Founding members keep this running.

$60 /year

Founding rate — locked for life. Regular price after launch: $96/year.

✓ Full access to all 158+ entries
✓ Print-ready reference card for every herb
✓ Monthly curated set — 5 herbs, one body system
✓ The Sunday Letter — weekly research digest
✓ Bookmarks synced across devices
✓ Founding rate locked forever

Become a founding member

Cancel any time. No questions asked.

THYROID FUNCTION

Iodine

I — Element #53

also known as Potassium iodide, Sodium iodide, Iodized salt, Iodide

An essential trace mineral the body uses to make thyroid hormones — and the thyroid uses it for almost everything else. Both deficiency and excess cause thyroid problems, which makes iodine one of the few nutrients where 'more' is not better.

Role in the body Structural component of thyroid hormones T3 and T4; thyroid gland concentrates iodine ~30 times higher than blood levels

Recommended daily intake

Adults · 150 mcg
Pregnancy · 220 mcg
Lactation · 290 mcg
Children 1 8 · 90 mcg
Children 9 13 · 120 mcg

Upper intake limit

1,100 mcg/day for adults

Signs of deficiency

Goiter — visible enlargement of the thyroid gland
Hypothyroidism — fatigue, weight gain, cold intolerance, depression, slow thinking
In pregnancy: increased miscarriage risk, fetal cognitive impairment
In children: impaired growth and brain development

Essential building block for thyroid hormones, which regulate metabolism, growth, and energy
Critical during pregnancy for fetal brain development — deficiency in pregnancy causes preventable cognitive impairment
Iodized salt has nearly eliminated severe iodine deficiency in countries that adopted it
Found naturally in seaweed, fish, dairy, and eggs
Supports normal growth and brain development in children

Active in I⁻ (iodide), IO₃⁻ (iodate).

Both too little and too much iodine cause thyroid problems — there is a narrow optimal range

Excess intake can trigger thyroid dysfunction in susceptible people, including autoimmune thyroiditis

People with Hashimoto's, Graves' disease, or other thyroid conditions should not supplement iodine without provider guidance

Seaweed supplements vary wildly in iodine content — some kelp products contain 50 to 100 times the daily limit per serving

Use caution with thyroid medications — iodine intake affects how they work

Pregnancy and nursing have higher needs but also more sensitivity to excess

Acute high-dose ingestion is a poisoning risk — kelp pills have caused thyroid storms

NIH ODS — Iodine · MedlinePlus — Iodine · Britannica — Iodine

Works with

Selenium Iodine is the substrate for thyroid hormone synthesis; selenium protects the gland via glutathione peroxidase. Both are essential for optimal thyroid function.

You might also explore

The curious few.

50 founding spots left