In the history of nutrition science, iodine is part of a public health triumph story. Prior to the 1920s, certain segments of our population had severe iodine deficiency – even disqualifying many men from military service in World War I. So, the United States implemented a simple program: Iodine was added to table salt. This act served to virtually eliminate the problem of severe iodine deficiency in our country. Since then, iodine receives little attention as a potential problem nutrient. However, emerging research is beginning to raise alarms among scientists that perhaps we need to look closer at mild to moderate iodine deficiency, especially in pregnant and breastfeeding women.
Iodine is a mineral that is found naturally in the soil of coastal areas. A deficiency in iodine causes problems with the thyroid gland, and people who suffer from a severe iodine deficiency will develop a noticeable goiter. More troubling than this, severe iodine deficiency worldwide is the single greatest cause of preventable mental retardation, causing a condition known as cretinism. While the impact of this severe deficiency is well-documented, mild to moderate iodine deficiency is more subtle and less understood.
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Scientists have known for some time that iodine is critical for assisting in the development of a baby's brain and nervous system. However, there has been little to no evidence linking mild iodine deficiency to problems in brain development – until now. A study recently published in The Lancet provides evidence that mild iodine deficiency in pregnancy may be a factor in a child's IQ later in life. The researchers used urine samples from 1,040 pregnant women in England and followed up eight years later by testing their children's IQ scores. They found that the women who had lower urinary iodine during pregnancy (indicating that they were mildly to moderately deficient in iodine) were more likely to have children with lower IQ scores at age 8, particularly in verbal and reading scores.
Other recent studies have added to this worry by indicating that mild iodine deficiency is an emerging problem in many countries. The difficulty is that iodine is found in few foods – mainly, the average American gets iodine from the use of iodized salt, as well as from dairy and some bread products. Interestingly, while most Americans consume too much salt, it is not usually iodized salt; this is because the salt used in processed food (a big chunk of our overall salt intake) is typically not the kind of salt that contains iodine. Adding to this problem, dairy intake is declining among parts of our population, and commercial bakeries are relying less on ingredients that contain iodine. Seafood is a great natural source of iodine, but seafood intake remains low overall in the U.S., especially for people not living near the coast. Finally, concerns about the safety of seafood have led many pregnant women to avoid it altogether while pregnant or breastfeeding.
[Read: What to Eat While Breastfeeding.]
In the U.S., pregnant women are advised to get 220 micrograms of iodine a day, while breastfeeding women should aim for 290 micrograms a day (compared to 150 micrograms a day for all other adults). One simple way to ensure you get enough iodine is to check your prenatal vitamin – make sure it provides about 150 micrograms. It's important not to overdo it; too much iodine can also be a problem.
Here are some of the top sources of iodine in your diet:
• 1/4 teaspoon iodized salt: 71 micrograms
• 1 cup yogurt: 75 micrograms
• 3 ounces baked cod: 99 micrograms
• 1 cup milk: 56 micrograms
• 1 gram seaweed: varies from 16 to 2,900 micrograms
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Melinda Johnson, MS, RD, is the Director of the Didactic Program in Dietetics and lecturer for the Nutrition Program at Arizona State University, and a Spokesperson for the Academy of Nutrition and Dietetics. Follow her on Twitter @MelindaRD.