Iodine, generally obtained from iodized salt, produces thyroid hormone, an essential component for normal brain development in the developing baby.
But as consumption of processed foods has increased, so has iodine deficiency because the salt in processed foods is not iodized, according to a policy statement from the American Academy of Pediatrics.
"This is the first time that the American Academy of Pediatrics has issued a statement on iodine," said Dr. Jerome Paulson, medical director for national and global affairs at the Children's National Health System and chair of the academy's Council on Environmental Health.
About one-third of pregnant women in the United States are iodine-deficient, according to background information in the article published online May 26 and in the June print issue of the journal Pediatrics.
Currently, only about 15 percent of pregnant and breast-feeding women take supplements containing iodide, the researchers said. Supplemental iodine is usually in the form of potassium iodide or sodium iodide, according to the U.S. National Library of Medicine.
Severe iodine deficiency is associated with stunted physical and mental growth, and even marginal iodine deficiency can decrease brain functioning, the report said.
Pregnant and breast-feeding women should take a supplement that includes at least 150 micrograms of iodide, and use iodized table salt, the academy said. Combined intake from food and supplements should be 290 to 1,100 micrograms a day. Potassium iodide is the preferred form, the doctors said.
Besides boosting brain development, iodine also appears to help protect babies from certain environmental harms.
The policy statement includes a recommendation to shield newborns from well water containing excessive nitrates and from cigarette smoke, both of which can harm the thyroid.
Why so few women take iodide supplements isn't clear, said Paulson. "It may be that most people don't appreciate the importance of adequate iodine in the diet for normal fetal development and that the women with marginal levels have no indication of their iodine status," he said. Iodine deficiency displays no symptoms.
Women thinking of getting pregnant can ask their doctor about iodide supplements, Paulson said. According to the report, a woman who is vegan or doesn't eat fish or dairy -- two food sources of iodine -- can ask about having a urine test to check for iodine deficiency.
Warning that supplement labels are misleading, the academy says the U.S. Food and Drug Administration should ensure that makers of prenatal vitamins use only potassium iodide and correct inconsistent labeling so that women understand what they are buying.
Women don't usually think about iodine deficiency, agreed Erin Corrigan, clinical nutrition manager at Miami Children's Hospital, who was not involved in the study. "I don't think it's on the top of the list for women for nutrients," she said. "We keep in mind folic, calcium and vitamin D."
Her patients are told to make sure their prenatal vitamin contains sufficient iodide and to continue taking it while they breast-feed.
To learn more about iodine intake, visit the American Thyroid Association.