Pregnant women and those planning to have children should ensure adequate iodine intake, according to the authors of a new report.
Lack of iodine, for which good dietary sources are milk, dairy products and fish, can lead to reduced mental development in their children, the study found.
Iodine is essential for producing the hormones made by the thyroid gland, which have a direct effect on foetal brain development.
A group of researchers from Surrey and Bristol universities, led by Margaret Rayman of the University of Surrey, used samples and data from Bristol-based Avon Longitudinal Study of Parents and Children (ALSPAC), also known as ‘Children of the 90s’. This is 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.
The researchers measured the iodine concentration in urine samples taken in the first trimester from 1,040 pregnant women, classifying 67 per cent as being iodine deficient.
Mental development of their children was assessed by measuring child IQ at age eight, and reading ability at nine.
Adjusting the results for external factors likely to affect these scores, such as parental education and breast-feeding, the researchers found that 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.
Rayman 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 iodine deficient.”
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 research was reported in The Lancet.