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 National Children’s Study Data Used to Study Iodine Levels in Pregnant Women

Iodine element

National Children’s Study (NCS) researchers recently published a report in the journal, Thyroid that noted low levels of iodine in pregnant women.   The study used data on pregnant women included in the National Health and Nutrition Examination Survey (NHANES) and the NCS Vanguard pilot study.

Iodine is needed to prevent growth disorders and problems with metabolism.  In the United States, most people get iodine from dairy products, like eggs and milk.  Other foods high in iodine include shrimp, some kinds of fish, and turkey breast.  Iodine intake in pregnant women and young children is essential for brain development, and iodine deficiency during these critical periods can have devastating consequences for a child’s IQ.  The Institute of Medicine recommends that pregnant women get 220 micrograms of iodine per day.   According to NCS researchers, about half of all multivitamins and prenatal vitamins contain iodine; underscoring the reason for pregnant women to incorporate iodine rich foods into their diet. 

Researchers measured iodine levels in urine and found that although levels in the U.S. population were in adequate range overall, almost 56 percent of NHANES pregnant women and 45 percent of NCS pregnant women did not have enough iodine in their urine.   The lowest levels were found in non-Hispanic black participants, which was also a group that had the lowest dairy product consumption.  They also observed that iodine levels changed based on where people live, with inadequate iodine levels in more than half of pregnant women in three out of the seven NCS geographic locations.

Kathleen Caldwell, one of the articles authors, stated, “the NCS and NHANES datasets combined provide the largest U.S. sample of urinary iodine concentrations in pregnant women. It is also the first U.S. study to report trimester-specific and region-specific urine iodine measures. The data indicate that median urinary iodine concentration values in pregnant women were low in the first and second trimesters, and normalized by the third trimester.” This may mean that health educators and researchers should do more health education for women who are pregnant or planning to become pregnant, so that they can make sure they get enough iodine in their diets. Since both sets of data showed that non-Hispanic blacks have especially low iodine levels, this group may need direct outreach and education.

A recent study by Dr. Sarah C. Bath and colleagues at the University of Surrey in Guildford (using data from the Avon Longitudinal Study of Children and Parents (ALSPAC) investigated whether mild iodine deficiency during early pregnancy had a negative effect on child cognitive development.  Their report, published in May 2013 in Lancet, found that more than half of the women in their study had iodine levels that were too low during the first trimester of pregnancy, and that children born to these women were more likely to have lower IQ scores at eight years of age and lower reading scores at nine years of age than children born to women with adequate iodine levels.

Taken together, these reports suggest some important areas for medical and public health efforts to promote optimal child health.  Dr. Caldwell and other NCS researchers plan to study additional nutritional markers and environmental chemicals in the NCS Vanguard pilot study.