Study: Iodine Deficiency In Pregnant Women May Harm Babies' IQs

24 May 2013 --- Iodine deficiency during pregnancy may have a negative effect on babies' mental development, according to new research published in The Lancet.

Iodine is ingested mainly through dairy products and seafood and is crucial for obtaining hormones secreted by the thyroid gland - which have a direct effect on fetal brain development.

Negative effects of iodine on brain development have long been known, however, few studies analyzed the effect of moderate or mild iodine deficiency during pregnancy on the mental development of the baby.

A team of investigators from Surrey and Bristol universities, both in England, used data and samples from Bristol-based Avon Longitudinal Study of Parents and Children (ALSPAC), commonly called "Children of the 90s."

The ALSPAC is a long-term health research project in which over 14,000 mothers participated during pregnancy in 1991 and 1992 - the health and development of their offspring have been tracked closely ever since.

The researchers calculated the iodine concentration in urine samples taken in the first trimester from 1,040 pregnant women.

After reviewing guidelines from the World Health Organization on recommended amounts of iodine during pregnancy, they categorized women who had an iodine-to-creatinine ratio of under 150 μg/g as being iodine deficient, and those with a ratio of 150 μg/g or more as iodine sufficient.

More than two-thirds of the women (67%) were categorized at less than 150 μg/g. Cognitive development of the women's babies was examined by measuring child IQ at age 8, and reading skills at age 9.

After adjusting the findings for external factors such as parental education and breast-feeding, the researchers found that the offspring of women in the iodine deficient category were much more likely to have low scores of verbal IQ, reading comprehension, and reading accuracy.

Additionally, the lower the mother's concentration of iodine, the lower the average scores for reading ability and IQ were in the kids.

Dr Sarah Bath, a co-author and registered dietician says: "Pregnant women and those planning a pregnancy should ensure adequate iodine intake; good dietary sources are milk, dairy products and fish. Women who avoid these foods and are seeking alternative iodine sources can consult the iodine fact sheet that we have developed, which is available on the web-sites of the University of Surrey and the British Dietetic Association. Kelp supplements should be avoided as they may have excessive levels of iodine."

The current study also adjusted for the mothers' intake of omega-3 fatty acids as a possible confounder on the effects on mental development - suggesting that these effects could have had more to do with iodine concentrations than previously thought.

Alex Stagnaro-Green of George Washington University, Washington DC, USA, in a linked comment regarding the findings said: "should be regarded as a call to action to public health policy makers in the UK. Absence of a public health policy in the face of clear documentation of moderate iodine deficiency and strong evidence of its deleterious effect on the neurodevelopment of children is ill advised. Nor should unmonitored and adventitious dietary iodine sources continue to be relied on. Until measures are taken to ensure that iodine needs can be met by usual dietary sources, pregnant and breastfeeding women should insist that the prenatal vitamins they are prescribed contain iodine."

A similar study also done this month and published in the Journal of Clinical Endocrinology & Metabolism (JCEM) suggested that mild iodine deficiency can harm the baby's neurological development. Children who did not receive adequate amounts of iodine while in the womb had lower scores on literacy tests when they were nine years old.