Children born to mothers who were mildly to moderately deficient in iodine during pregnancy are at higher risks of impaired mental development, a worrying new British study has found.

This research strengthens the findings of a recent Tasmanian study which showed that iodine deficiency in the womb caused children to perform less well in grammar, English-literacy tests and spelling. The study also found that an iodine-fortified diet during childhood did not reverse the effects of prenatal iodine deficiency.

Iodine and the brain – what’s the link?

Thyroid hormones are involved in the proper development of the foetus’ brain and nervous system. These hormones are produced by the thyroid glands which require iodine for their synthesis.

Insufficient iodine (and thus thyroid hormones) during foetal brain development may cause poor neuron growth as well as slower communication between the brain and nerve cells.

Study details

Led by Dr Margaret Rayman from the University of Surrey, the researchers used samples and data from the Avon Longitudinal Study of Parents and Children (ALSPAC). They analysed the iodine concentration of urine samples collected from 1,040 pregnant women during their first trimester.

To assess the children’s mental development, the scientists assessed their IQ and their reading aptitudes, at age eight and nine respectively.

Study findings

“Our results clearly show the importance of adequate iodine status during early pregnancy, and emphasise the risk that iodine deficiency can pose to the developing infant,” Dr Rayman, declared in a news release.

Two thirds of the women involved were iodine deficient and tests showed that their children had a lower verbal IQ and a poorer reading accuracy and comprehension.

That’s not all, it also appears that as the mother’s iodine status during pregnancy declines, so does the child’s potential in terms of IQ and reading ability.

What this means for you

Whether you’re trying to conceive or you already have a bun in the oven, make sure your iodine stores are adequate — a test analysing your urinary iodine concentration can help you figure this out.

If your urine specimen indicates an iodine deficiency, don’t fret: talk to your GP concerning the needs for a supplement.

And if you’re breastfeeding, you may also want to maintain a healthy iodine status since your baby’s brain is still developing.

Iodine-rich foods

  • Milk and dairy products including yoghurt
  • Fish and seafood
  • Eggs
  • Potatoes with the skin
  • Iodised salt
  • Iodine fortified breads

You’ll notice that we didn’t mention kelp or seaweed — although these are very rich in iodine, they may provide an excessive amount of iodine. You can have too much of a good thing: when consumed in excess during pregnancy, iodine can cause mental retardation as well as birth defects.

Conventional milk vs. organic milk

Have you come across articles stating that organic milk during pregnancy can harm a baby’s IQ? Well, that’s a far-fetched title: while it’s true that organic milk contains less iodine than conventional one, it will definitely not harm your baby’s brain development. You simply have to include more iodine-rich foods in your diet.

To help your baby have the best start in life, you can also make sure that you eat a varied, balanced diet.


    Bath et al (2013) Effect of inadequate iodine status in UK pregnant women on cognitive outcomes in their children: results from the Avon Longitudinal Study of Parents and Children (ALSPAC). Lancet. S0140-6736(13)60436-5.