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Shaky Amount of Iodine in U.S. Salt
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Some 'Iodine-Fortified' Table Salt Falls Short of Recommended Levels of the Nutrient, Study Shows
Reviewed By Louise Chang, MD
Feb. 1, 2008 -- There are fewer food sources of iodine in the American diet than there were just a few decades ago, raising the risk of iodine deficiency in a growing number of people. So says a researcher who calls himself an "iodine activist."
Even people who buy and use iodine-fortified table salt may be at risk, says Purnendu K. Dasgupta, PhD, a chemistry professor at the University of Texas at Arlington.
Dasgupta and colleagues recently tested 88 samples of iodized salt and found that 47 of them, or 53%, did not meet the U.S. Food and Drug Administration's recommendations for iodine levels.
Iodine levels tended to decrease in individual containers with exposure to humidity, but light and heat had little effect.
The findings are published in the latest online issue of the American Chemical Society journal Environmental Science and Technology.
"We certainly are not saying that people need to eat more salt," Dasgupta says. "But if we had mandatory iodization of all salt used in food, that would solve the problem."
Most Salt Has No Iodine
Iodized salt is now the main source of iodine in the American diet, but only about 20% of the salt Americans eat contains the micronutrient, Dasgupta says.
Increasing popular "designer" table salts, such as sea salts and Kosher salts, usually do not have iodine, and neither does salt used in most fast foods and processed foods.
Add to this the fact that iodine is no longer used in the production of commercial breads and dairy products, plus the ever-present public health warnings about restricting dietary salt, and iodine deficiency becomes a real threat for some people in the United States, Dasgupta says.
Though government nutrition surveys suggest that iodine deficiency is not a problem in the United States at the population level, Dasgupta says this may not be the case for the most vulnerable subgroups: pregnant and nursing women, babies, and young children.
Iodine is important in the production of thyroid hormones and critical to normal brain development in newborn infants and children. Iodine deficiency is the leading preventable cause of cretinism in the developing world. And at least one study suggests that children in developed countries born to iodine-deficient moms may have an increased risk of attention deficit hyperactivity disorder (ADHD).
Pregnant Women Need Iodine
Boston University Medical Center endocrinologist Elizabeth Pearce, MD, tells WebMD her research suggests that about half of pregnant and nursing women are not getting enough iodine in their diets.
In her latest study, published last May, sampled breast milk from 47% of nursing mothers did not contain sufficient iodine to meet their infants' nutritional needs.
One problem, she says, is that only about a third of over-the-counter vitamins recommended for pregnant and nursing women and two-thirds of prescription prenatal vitamins contain iodine.
In 2006, the American Thyroid Association published guidelines recommending that all pregnant and breastfeeding women take prenatal vitamins containing iodine, but Pearce says few women have likely heard about the recommendation.
"It is very difficult to measure iodine deficiency in individuals," she says. "Because of this, and because pregnant and breastfeeding women are particularly vulnerable, these women should make sure that they take a vitamin with iodine."
SOURCES: Dasgupta, P.K., Environmental Science and Technology, Feb. 15, 2008; online edition. Purnendu K. Dasgupta, PhD, professor and chairman, department of chemistry, The University of Texas at Arlington. Elizabeth N. Pearce, MD, assistant professor of medicine, Boston University School of Medicine. Journal of Clinical Endocrinology and Metabolism, 2004. ATA Iodine Supplementation for Pregnancy and Lactation, Thyroid, 2006; vol. 16. Journal ofClinical Endocrinology andMetabolism, May 2007.
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