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Mild to moderate iodine deficiency during pregnancy may have a negative long-term impact on children's brain development, British researchers report.
Low levels of the so-called "trace element" in an expectant mother's diet appear to put her child at risk of poorer verbal and reading skills during the preteen years, the study authors found. Pregnant women can boost their iodine levels by eating enough dairy products and seafood, the researchers suggested.
The finding, published online May 22 in The Lancet, stems from an analysis of roughly 1,000 mother-child pairs who were tracked until the child reached the age of 9 years.
"Our results clearly show the importance of adequate iodine status during early pregnancy, and emphasize the risk that iodine deficiency can pose to the developing infant," study lead author Margaret Rayman, of the University of Surrey in Guildford, England, said in a journal news release.
The study authors explained that iodine is critical to the thyroid gland's hormone production process, which is known to have an impact on fetal brain development.
According to the World Health Organization, iodine "sufficiency" is defined as having a so-called iodine-to-creatinine ratio of 150 micrograms per gram (mcg/g) or more; those with a ratio falling below 150 mcg/g are deemed to be iodine "deficient."
By examining first-trimester urine sample data collected by a long-term study of parents and children based in Bristol, England, the study authors found that just over two-thirds of the mothers had been iodine-deficient while pregnant.
After adjusting for other factors (such as breast-feeding history and parental education), the researchers found that iodine deficiency during pregnancy raised the child's risk for having a lower verbal IQ, and poorer reading accuracy and comprehension by the time they turned 8 or 9.
What's more, the more iodine levels dropped during pregnancy, the lower the child's performance in terms of IQ and reading ability, the study authors noted.
Study co-author and registered dietitian Sarah Bath agreed that "pregnant women and those planning a pregnancy should ensure adequate iodine intake." She suggested in the news release that "good dietary sources are milk, dairy products and fish. . . . Kelp supplements should be avoided as they may have excessive levels of iodine."
The U.S. National Institutes of Health states that 3 ounces of baked cod contains approximately 99 mcg of iodine, 1 cup of plain low-fat yogurt contains about 75 mcg, and 1 cup of reduced-fat milk has an estimated 56 mcg.