Quick answer

Women need 150 mcg of iodine a day, rising to 220 mcg in pregnancy and 290 mcg while breastfeeding. The American Thyroid Association advises 150 mcg a day from a supplement from the time a pregnancy is planned until breastfeeding ends. Not every prenatal vitamin contains iodine, so check the label.^1,2,3

Key facts

During pregnancy the body makes about 50% more of the thyroid hormone T4, which is why iodine needs rise.¹
Women of reproductive age in the US had a median urinary iodine of 119 mcg/L in 2007 to 2014.¹
Of 59 best-selling prenatal vitamins, 25 contained no iodine.³
Women who limit salt tend to have lower iodine levels than women who do not.¹

How much women need

Pregnant women need 220 mcg of iodine a day and breastfeeding women 290 mcg. The World Health Organization recommends 250 mcg a day for both.^1,2

Early in pregnancy, before the baby's own thyroid is working, the baby depends entirely on the mother's T4, so her iodine supply matters from the start. After birth, breast milk carries iodine to the baby, which is why the need peaks while breastfeeding.¹

The supplement recommendation

The American Thyroid Association recommends a daily supplement with 150 mcg of iodine as potassium iodide for women who are planning a pregnancy, pregnant or breastfeeding. The American Academy of Pediatrics recommends at least 150 mcg and the use of iodized salt.^1,2

Where iodized salt reaches people unevenly, the World Health Organization recommends supplements for all women of childbearing age to reach 150 mcg a day, and 250 mcg a day from food and supplements during pregnancy and breastfeeding.¹

What the evidence shows

Helps women who are pregnant, breastfeeding or planning a pregnancy meet their higher iodine needs*^1,2,4

Moderate evidence

Needs rise from 150 mcg a day to 220 mcg in pregnancy and 290 mcg while breastfeeding, because the mother makes about 50% more thyroid hormone and the baby depends on it early in pregnancy. US surveys suggest many pregnant women get somewhat less than they need, and the American Thyroid Association and the American Academy of Pediatrics recommend a daily supplement with 150 mcg. Trials have not shown that the supplement changes children's development: in two trials of 150 or 200 mcg a day, children's thinking, language and movement scores did not differ, and a Cochrane review found too little data to judge.

Amount studied: 150 mcg a day as potassium iodide, the amount the American Thyroid Association recommends

Put simply, the advice rests on the body's higher need and on surveys of intake, not on trials showing better outcomes for children. A Cochrane review of 14 trials judged the data too limited to reach firm conclusions either way.^1,4

Are US women getting enough?

Pregnant women in the US had a median urinary iodine of 144 mcg/L in 2007 to 2014, just under the 150 mcg/L that marks enough in pregnancy. Those who had eaten no dairy in the past day had a median of 100 mcg/L, against 163 mcg/L in those who had.¹

In 2011 to 2014, 72.2% of pregnant women in the US took a dietary supplement, but only 17.8% took one containing iodine; among breastfeeding women the figures were 75% and 19%.¹

Prenatal vitamins differ. In a survey of 59 best-selling brands, 34 listed iodine, at 25 to 290 mcg per daily serving, and some got it from kelp, whose iodine is less predictable. Look for iodine and its amount in micrograms on the Supplement Facts panel.³

While breastfeeding

In a study of 57 breastfeeding women in the Boston area, the median iodine in breast milk was 155 mcg/L, and the authors estimated that 47% of the women may have been providing too little for their babies.¹

A breastfed baby gets iodine from milk, and how much the milk holds depends on the mother's intake. That is why the advice to take iodine continues for as long as you breastfeed.^1,2

Cautions

In a Spanish study, pregnant women who took 200 mcg or more of iodine a day from supplements were more likely to have raised TSH than those taking less than 100 mcg, a sign that high doses may disturb thyroid function in some women.¹

Prescription potassium iodide carries a warning that it can harm the fetus and cause goiter when taken in pregnancy. That concerns drug doses far above the 150 mcg in a prenatal supplement, but it is a reason to avoid high-dose iodine products while pregnant.⁵

Very high doses of 1,500 to 6,000 mcg a day have been studied for breast pain in fibrocystic breast disease. They are several times the adult upper limit and should be used only under a doctor's guidance.^1,2

Ask first if you have a thyroid condition or take thyroid medicine
Ask first before taking more iodine than your prenatal vitamin provides
Ask first before taking kelp or an iodine-only product while pregnant or breastfeeding

Questions people ask

Do I need an iodine supplement if my prenatal vitamin has none?

The American Thyroid Association recommends 150 mcg a day from a supplement during pregnancy and breastfeeding, so ask your provider whether to switch prenatal vitamins or add iodine. Many prenatal vitamins sold in the US contain none.^1,3

Should women who are not planning a pregnancy take iodine?

Most do not need to. Women who are not pregnant or breastfeeding need 150 mcg a day, which most US diets with dairy, seafood, eggs or iodized salt provide.²

Is iodine safe while breastfeeding?

At the recommended amount, experts advise 150 mcg a day from a supplement while breastfeeding, because milk is the baby's source. High doses are different: the prescription potassium iodide label warns that it passes into milk and can cause rash and thyroid suppression in the baby.^1,5

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Sources

*These statements have not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure, or prevent any disease.

This page is information, not medical advice. Talk to your doctor or pharmacist about your own situation.