Salt: Bad for Blood Pressure But Good for Some (cont.)
Yet getting too little iodine -- called iodine deficiency -- is a serious issue. Iodine is an essential mineral for the production of thyroid hormones. Too little iodine in a pregnant women's diet can affect the development of the fetus' brain and can cause cretinism, an irreversible form of physical and mental retardation. Iodine deficiency during infancy can also result in abnormal brain development and impaired intellectual development.
"The developing brain is the most sensitive organ. Iodine deficiency doesn't make people idiots, but it does make them less smart," says Maberly.
In the U.S., iodine deficiency is more common in women than men. It's also common in pregnant women and adolescents, he tells WebMD.
Iodine deficiency is thought to be rare in the U.S. It's considered a problem of third-world countries, but Maberly disagrees. "Iodine nutrition in the U.S. is borderline," he tells WebMD. "A pregnant woman may not be protected. Even if she eats a normal diet, her intake is probably inadequate. Only 70% of table salt is iodine-fortified."
Until nearly five years ago, Americans who got dairy, bread, and meat in their diets got plenty of iodine, he explains. Machines used in production were cleaned with an iodine disinfecting solution, so some iodine ended up in dairy, bread, meat products. That ended when companies quit using iodine disinfectant.
Iodized salt is rarely found in canned, frozen, or boxed food, says Maberly. French fries and other snack foods mostly contain regular salt -- not iodized salt.
In fact, Americans now get one-third less iodine than they once did, he notes.
Both newborns and toddlers are affected by iodine deficiency. A recent study showed lower IQ scores among children with mild iodine deficiency -- proof that the problem exists in developed countries, writes researcher Piedad Santiago-Fernandez, MD, an endocrinologist at the Complejo Hospitalario Carlos Haya in Malaga, Spain.
It's true, says Michael Karl, MD, an endocrinologist with the University of Miami School of Medicine. "You can certainly see even subtle changes in iodine can affect IQ," Karl tells WebMD. "Iodine is critical in the first years of life, extraordinarily important up to 3 or 5 years of age."
Children in financially stressed families are likely at highest risk. They rarely take multivitamins, he tells WebMD. "Iodine deficiency is not an epidemic yet, but it's serious enough that it should be watched."
Sea salt and most salt substitutes are not iodized. Unless fruits and vegetables are grown in iodine-rich soil, they will not contain iodine. Restaurants usually order salt in bulk, and often it's not iodized salt.
However, anything from the sea - such as seaweed (kelp) or fish -- can be a good source of iodine, says Maberly. A cup of cow's milk contains nearly 100 micrograms of iodine. Some breads contain iodine, but not all.