NEW RESEARCH HAS raised concerns that the iodine status of pregnant women is a public health issue that needs to be addressed, after it found that an iodine deficiency in pregnancy may have an adverse effect on children’s mental development.
Iodine is essential for producing the hormones made by the thyroid gland, which have a direct effect on fetal brain development. Humans mostly consume iodine through dairy products and seafood.
The potentially harmful effects of severe iodine deficiency on brain development are well-established, however few studies have examined the effect of mild or moderate iodine deficiency during pregnancy on the cognitive development of a child. The recent recognition of mild-to-moderate iodine deficiency in some UK population groups, including pregnant women, has allowed this effect to be investigated.
Researchers 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 project involved more than 14,000 pregnant women in 1991 and 1992, and the health and development of their children has been followed by scientists ever since.
Researchers measured the iodine concentration in urine samples taken in the first trimester from 1,040 pregnant women. Referring to World Health Organisation (WHO) guidelines on recommended concentrations of iodine during pregnancy, they classified women who had an iodine-to-creatinine ratio [1] of less than 150 μg/g as being iodine deficient, and those with a ratio of 150 μg/g or more as iodine sufficient. Over two thirds (67 per cent) of the women fell into the category of “iodine deficient”.
The babies born underwent mental development assessments which involved measuring child IQ at age eight and reading ability at age 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 (lower quartile) of verbal IQ, reading accuracy, and reading comprehension. The research, published in the Lancet medical journal, found that the lower the mother’s concentration of iodine, the lower were the average scores for IQ and reading ability in the children.
According to Margaret Rayman of the University of Surrey, in Guildford, UK, who led the research, the 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.”
Dr Sarah Bath, a co-author and registered dietitian, advised that pregnant women and those planning a pregnancy should ensure adequate iodine intake, listing good dietary sources of iodine as 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,” she said.
Professor Jean Golding OBE, another co-author and ALSPAC founder, the study “provides further strong evidence of the importance of eating iodine-rich foods like fish during pregnancy.”
Previous results from ALSPAC have indicated that a mother’s consumption of seafood during pregnancy was associated with her child’s mental development, with lower seafood consumption associated with poorer scores in reading and IQ tests. Originally, researchers speculated that this might be due to higher levels of omega-3 fatty acids in seafood, but the current study – which also adjusted for mothers’ intake of omega-3 fatty acids as a possible confounding variable on the effects on cognitive development – suggests otherwise.
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