The two separate research studies, published in the Lancet and the Journal of Clinical Endocrinology & Metabolism (JCEM), suggest that even a milk deficiency in iodine during pregnancy may result in reduced mental development that has long term effects for children’s intelligence scores.
The findings suggest maternal iodine deficiency to be an important public health issue that needs to be addressed, warned the scientists behind the UK research published in the Lancet.
Led by Professor Margaret Rayman from the University of Surrey, the UK team noted that while there is well-established evidence linking extreme iodine deficiency to problems with brain development, there is ‘considerably less’ research focused on the possible effects of mild to moderate deficiency on an unborn child’s cognitive development.
“Low maternal iodine status was associated with an increased risk of suboptimum scores for verbal IQ at age 8 years, and reading accuracy, comprehension, and reading score at age 9 years, even after adjustment for many potential confounders,” wrote the authors.
Lower IQ scores
Ryman and her team of UK researchers analysed data from 1,000 mothers who were part of the ‘Children of the 90s’ study – which followed the development of children born to 14,000 mothers in Avon since 1990-91.
The team reported that 67% of mothers had levels of iodine below that recommended by the World Health Organisation.
Children were then divided into groups according to how well they performed on IQ and reading tests at ages eight and nine, with the team finding that those children whose mothers had low iodine levels were 60% more likely to be in the bottom group.
“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,” Rayman said.
Reading ability
In a separate research paper, published in the JCEM, researchers from Australia also found that inadequate iodine exposure during pregnancy was associated with lasting effects on children’s literacy scores.
"Our research found children may continue to experience the effects of insufficient iodine for years after birth," said Dr Kristen Hynes from the University of Tasmania – who led the research.
"Although the participants' diet was fortified with iodine during childhood, later supplementation was not enough to reverse the impact of the deficiency during the mother's pregnancy."
The longitudinal study examined standardised test scores of 228 children – finding that children whose mothers had urinary iodine concentrations of less than 150μg/L had reductions of 10% in spelling, 7.6% in grammar, and 5.7% in English-literacy performance compared with children whose mothers' iodine levels were above the 150μg/L level.
However, the team noted that inadequate iodine exposure was not associated with lower scores on math tests.
"Fortunately, iodine deficiency during pregnancy and the resulting neurological impact is preventable," Hynes said. "Pregnant women should follow public health guidelines and take daily dietary supplements containing iodine.
“Public health supplementation programs also can play a key role in monitoring how much iodine the population is receiving and acting to ensure at-risk groups receive enough iodine in the diet," she said.