Iodine: What It Does, How Much You Need, and Where to Get It

A small mineral with a big job: making the thyroid hormones that run your metabolism.

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By the Ration Editorial Team · Reviewed against primary research · Updated July 14, 2026

Iodine is a trace mineral found in soil and seawater.

Your body cannot make it. It has to come from food, water, or supplements.

The thyroid gland uses iodine as a raw material. It combines iodine with the amino acid tyrosine to build the hormones thyroxine (T4) and triiodothyronine (T3).

These hormones touch nearly every cell in the body. They set your resting metabolic rate, support normal growth, and are especially important for brain development before and after birth.

The thyroid gland traps iodine from the bloodstream and stores it until it is needed.

When iodine levels are low, the thyroid cannot make enough T4 and T3. The pituitary gland senses this and releases more thyroid stimulating hormone (TSH), pushing the thyroid to work harder.

Over time, this extra stimulation can cause the thyroid to enlarge, a condition known as a goiter.

Thyroid hormones also cross the placenta during pregnancy. This is why iodine status in early pregnancy matters so much for fetal brain and nervous system development.

Iodine deficiency is one of the most common preventable causes of intellectual disability worldwide.

Signs and consequences of low iodine can include:

• Goiter, or a visibly enlarged thyroid gland
• Hypothyroidism, with fatigue, weight gain, and cold intolerance
• Impaired growth and cognitive development in children
• Miscarriage or stillbirth risk in severe deficiency during pregnancy
• Reduced IQ in children born to iodine deficient mothers

Mild to moderate deficiency has crept back into some higher income countries as people cut back on iodized salt and dairy for health or dietary reasons.

• Pregnant and breastfeeding people, who need more iodine for fetal and infant development
• People who avoid iodized salt, such as those using sea salt or kosher salt exclusively
• People following vegan or dairy free diets without seaweed or iodized salt
• People living in regions with iodine poor soil
• People who eat little seafood or dairy

Iodine content in food depends heavily on soil and water content, and on whether salt used in processing is iodized.

Seaweed, including kelp and nori, is by far the most concentrated natural source and can sometimes provide far more iodine than needed in a single serving.

Iodized salt was introduced in many countries specifically to prevent deficiency at a population level, and it remains one of the most reliable sources for people who use table salt regularly.

Needs vary by life stage, with pregnancy and breastfeeding requiring notably more than average adult needs.

• Adults generally need around 150 micrograms per day
• Pregnant people generally need more, often cited around 220 to 250 micrograms per day
• Breastfeeding people generally need the highest amounts, often cited around 250 to 290 micrograms per day
• Children need less than adults, scaled to age

These figures are general reference ranges rather than personalized targets, and actual guidelines vary by country and health authority.

Iodine follows a U shaped risk curve. Both too little and too much can disrupt thyroid function.

Excess iodine, often from high dose supplements or regular heavy seaweed consumption, has been linked to:

• Iodine induced hyperthyroidism, especially in people with pre-existing thyroid nodules
• Worsening of autoimmune thyroid conditions like Hashimoto's thyroiditis
• Paradoxical hypothyroidism in some sensitive individuals
• Thyroid gland enlargement similar to that seen in deficiency

People with known thyroid disease are generally more sensitive to both iodine excess and deficiency, which is part of why thyroid conditions warrant individualized medical guidance rather than generic supplementation.

Most people eating a varied diet with iodized salt, dairy, eggs, or seafood meet their iodine needs without supplements.

Prenatal vitamins often include iodine specifically because pregnancy needs are higher and deficiency risk carries outsized consequences for fetal development.

People considering a supplement, particularly those who are pregnant, vegan, or avoid iodized salt, may want to look at their overall diet pattern first, since food sources are generally easier to keep within a safe range than concentrated supplements or seaweed products.

Iodine is a small but essential mineral that your thyroid depends on to keep metabolism, growth, and brain development running normally.

Most people covering their bases with iodized salt, dairy, eggs, or seafood do not need to think much about it.

Pregnant people, strict vegans, and those who avoid iodized salt are the groups most worth paying closer attention to, while anyone with existing thyroid disease should be cautious about swinging iodine intake sharply in either direction.