Adjusting the results for external factors likely to affect these scores, such as parental education and breast-feeding, researchers found children of women in the iodine-deficient group were significantly more likely to have low scores of verbal IQ, reading accuracy and reading comprehension.
The lower the mother's concentration of iodine, the lower were the average scores for IQ and reading ability in the children.
The lead researcher in a report which suggests pregnant women and those planning to have children should nurture their iodine intake said iodine deficiency can pose a "risk" to infants.
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 iodine deficient.
– Professor Margaret Rayman of the University of Surrey
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.
– Dr Sarah Bath, a co-author and registered dietician
Women planning to have children and those who are already pregnant should ensure adequate iodine intake, authors of a new report have said.
The study found that a lack of iodine, found in milk, dairy products and fish, can lead to reduced mental development in their children.
It is essential for producing the hormones made by the thyroid gland, which have a direct effect on foetal brain development, it said.
A group of researchers from Surrey and Bristol universities undertook a long-term health research project in which more than 14,000 mothers enrolled during pregnancy in 1991 and 1992, and the health and development of their children has been followed in detail since.