Get Enough Iodine Mom, But...

Excess iodine while pregnant and breastfeeding women can lead to hypothyroidism in baby

(RxWiki News) Pregnant women need enough iodine for their baby's brain to develop well. But too much iodine can backfire by interrupting normal hormone production.

It's not typical for women to accidentally take too much iodine. But when these rare situations occur, it can lead to possible problems with the baby's brain development later.

"Get enough iodine — not too much."

A recent article described a case study of three babies who received way too much iodine. This was not a study of a large group, and there is no evidence that taking too much iodine is common in pregnant moms.

Instead, this article looked at a very specific set of situations where moms went overboard on their iodine.

The research, described by Kara Connelly, MD, from the Department of Pediatrics at Oregon Health & Science University's Doernbecher Children's Hospital, and her colleagues, involved three babies who had congenital hypothyroidism.

"Congenital" means they were born with the condition. The hypothyroidism means their thyroid gland did not produce enough of the hormone also called thyroid.

One of the nutrients that affects whether a baby produces the right amount of thyroid is how much iodine the mother consumes while pregnant.

The World Health Organization recommends that pregnant women get 200 to 300 µg of iodine daily to make sure their baby's brain develops properly and they have enough fetal thyroid hormone production.

The upper limit of what's safe for women to take, according to the U.S. Institute of Medicine, is 1,100 µg. More than that can cause hypothyroidism.

In this study, the mothers had taken 12.5mg of iodine each day while they were pregnant and/or breastfeeding. The baby receives the iodine through the placenta or breastmilk.

One milligram (mg) is equal to 1000 micrograms (µg), so 12.5mg is equal to 12,500 µg — more than 11 times the upper safe limit.

The three babies had blood iodine levels that were about 10 times higher than a normal baby's blood iodine levels.

Even though iodine is normally what helps the thyroid work, the thyroid has a sort of emergency shut-off valve when it senses too much iodine coming in.

The thyroid knows it can't over-produce its hormone — which would be hyperthyroidism — so it stops working altogether. ("Hypo" means "under/less" and "hyper" means "over/more".)

This thyroid shut-down didn't happen in the mothers because the bodies of adults and older children can override the shut-down when it realizes no thyroid is being produced.

But a small baby's body isn't developed enough to do that yet. Their thyroid gland is still immature, so it may stay shut down, which means no thyroid is being produced.

Over time, this hypothyroidism can lead to neurocognitive problems in babies.

The solution is for pregnant women to make sure they are getting the right amount of iodine — more than 200 or 300 µg but never more than 1,100 µg.

This can be tricky because multivitamins, including prenatal vitamins, usually already have iodine in it. If a woman is taking a prenatal vitamin and then also takes iodine supplements or seaweed/kelp supplements that contain iodine, she could get too much.

The study was published July 27 in The Journal of Pediatrics. Information was not provided regarding funding, but the authors declared they had no conflicts of interest related to the research.

Review Date: 
August 29, 2012