Babies who do not receive sufficient iodine in-utero are more likely to have poor literacy skills later in life according to a new longitudinal follow-up study published online in The Journal of Clinical Endocrinology & Metabolism (JCEM).

Functions of iodine

This trace element is vital for the proper regulation of the thyroid hormones — these are involved in several biochemical reactions which are essential for health.

During pregnancy, this mineral is required for the optimal development of the foetus’ brain and nervous system. For instance, thyroxine, a thyroid hormone is needed for the proper myelination of nerves cells — this process enables rapid and accurate communication between the various nerve cells throughout the body and the brain.

Severe deficiency of iodine during conception may cause cretinism, a type of irreversible mental retardation as well as severe speech and hearing issues.

Sources of iodine

Good sources of this mineral include kelp (a sea vegetable), seafood, dairy products, iodised salt and plants grown in an iodine-rich soil. Seaweeds (such as dulse, wakame and nori) are also good sources.

Oily fish rich in iodine: fresh tuna, salmon, mackerel and sardines — do not eat more than two portions per week.

You can also get some iodine in eggs, cheese, natural yogurt, bread and potatoes with the skin.

Study details

The Tasmanian population was considered to be mildly iodine deficient until the voluntary iodine fortification program of October 2001 in which bread manufacturers started using iodised salt. The researchers therefore analysed standardised test scores of 228 children whose mothers attended The Royal Hobart Hospital (Tasmania) antenatal clinics between 1999 and 2001.

In this study, iodine deficiency was defined as urinary iodine concentrations below 150μg/L.

Study findings

The authors state that the nine-year-old children whose mothers were iodine deficient during pregnancy had “poorer educational outcomes in primary school than peers whose mothers did not have gestational iodine deficiency. ”

These children scored significantly lower in spelling, grammar and in English-literacy tests even after adjusting for biological and socioeconomic confounders. Gestational iodine deficiency was not associated with lower performance on maths tests.

According to the researchers, the developing auditory pathways of the foetus — and therefore its auditory working memory — are the most affected by inadequate in-utero exposure to iodine. This has greater ramifications on the children’s spelling abilities than their mathematical reasoning aptitudes.

“Our research found children may continue to experience the effects of insufficient iodine for years after birth,” said the study’s lead author, Dr Kristen Hynes from the Menzies Research Institute at the University of Tasmania, Australia.

“Although the participants’ diet was fortified with iodine during childhood, later supplementation was not enough to reverse the impact of the deficiency during the mother’s pregnancy,” Dr Hynes added.

Study implications

“Fortunately, iodine deficiency during pregnancy and the resulting neurological impact is preventable. Pregnant women should follow public health guidelines and take daily dietary supplements containing iodine,” Dr Hynes commented.

According to the Department of Health, expectant mothers may need to consider complementing their dietary iodine intake with supplements. Ask your GP to assess your personal requirements for a supplement especially if you feel your diet could be lacking in iodine.


    Hynes et al (2013) Mild iodine deficiency during pregnancy is associated with reduced educational outcomes in the offspring: 9-year follow-up of the gestational iodine cohort. J Clin Endocrinol Metab. 98(5):1954-62.