In a study of 1,040 mothers and their children, researchers found that mothers who were classified as iodine deficient had children that scored lower on IQ tests and reading tests, than those whose mother’s were iodine sufficient.
The researchers measured the iodine concentration in urine samples of pregnant women during their first trimester and, based on World Health Organisation (WHO) guidelines on recommended concentrations of iodine during pregnancy, found that 67 per cent of the women were iodine deficient.
The children were then tested at the age of eight for IQ levels and for their reading age at the age of nine. After other factors such as parental education and breast-feeding were taken into account, researchers found that the children of women in the iodine-deficient group were significantly more likely to have lower scores of verbal IQ, reading accuracy and reading concentration.
In fact, the lower the mothers’ concentration of iodine, the lower the average scores for IQ and reading ability in children.
Professor Margaret Rayman, from the University of Surrey and the lead researcher, said, ‘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 even in a country classified as only mildly deficient.’
Dr Sarah Bath, a co-author and registered dietician, said, ‘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 websites of the University of Surrey and the British Dietetic Association. Kelp supplements should be avoided as they may have excessive levels of iodine.’
The study used samples and data from the Bristol-based Avon Longitudinal Study of Parents and Children (ALSPAC), also known as the Children of the 90s. This study is a long-term health research project in which more than 14,000 mothers enrolled during pregnancy in 1991 and 1992. The health development of the children has been followed since birth.
Previous results from the study indicated that a mother’s consumption of seafood during pregnancy was associated with her child’s cognitive development. Lower seafood consumption was associated with poorer scores in reading and IQ tests.
At the time researchers though this might be due to high levels of omega-3 fatty acids in seafood, but the current study - which took into account mothers' intake of omega-3 fatty acids - suggests that these effects could have been more to do with iodine levels than previously thought.
Alex Stagnaro-Green from George Washington University, Washington DC, said, ‘The findings 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.’
Iodine is found in dairy and seafood and is essential for producing the hormones made by the thyroid gland, which has a direct effect on foetal brain development. There have been a number of studies establishing the connection between severely low iodine levels and foetal brain development but there are very few studies examining the effect of mild or moderate iodine deficiency.
