Iodine, a Critically Overlooked Nutrient

Iodine is a trace element required by the body for an increasing number of identified physiologic functions. This element belongs to the halogen family of elements, a group of highly reactive nonmetals that includes fluorine, chlorine, bromine, and astatine. Iodine is found naturally in large amounts in seafood such as kelp and saltwater fish. Most iodine intake in the United States is from iodized table salt. Iodation of salt in the United States began in the 1920s in response to the large number of goiters in certain populations in areas where soil and water levels of iodine were low. The upper Midwest and Great Lakes region, where the incidence of goiter was as high as 30–40% in 1922, was named the “goiter belt.”1 Currently, the recommended daily allowance (RDA) of iodine for adults is 150 μg/day, for pregnant women 220 μg/day, and for lactating women 290 μg/day, and although some studies indicate that Americans’ iodine intake is adequate, many other studies suggest a prevalence of subclinical iodine deficiency. In this regard, it is worth considering that although many Americans consume large amounts of sodium in processed foods, many such foods do not use the iodized form of salt, and even if they do, research suggests that only 10% of the iodide in iodized salt is bioavailable.2 Moreover, with cautionary recommendations that Americans limit their sodium intake, an adequate intake of iodine is of concern because iodine deficiency is associated with numerous abnormalities including hypothyroidism, goiter, cretinism, cognitive disorders, neurologic disorders, and breast disease. Iodine deficiency is especially hazardous in pregnant women, developing fetuses, and newborn infants because of its ability to cause irreversible damage to fetuses and newborns. The World Health Organization (WHO) has established that the mean urine iodine concentration should not exceed 10 μg/dL, and should be less than 5 μg/dL in no more than 20% percent of a population. The National Health and Nutrition Examination Surveys (NHANES), which periodically measure urine iodine concentrations to evaluate iodine status in the population of the United States, indicate that it has an adequate iodine intake. Moreover, because the adult RDA for iodine is 150 μg/day, and goiter is controlled with only 0.05 mg of iodide per day, many scientists believe that iodine intake is sufficient. However, between NHANES I (1971–1974) and NHANES III (1988–1994), Americans’ median urine iodine concentration decreased by 50%, while a low urine excretory level of iodine, of less than 5 μg/dL, increased by 4.5-fold in this same period. Monitoring of high-risk groups showed that 6.7% of pregnant women and 14.9% of women of childbearing age had a urine excretory level of less than 5 μg/dL of iodine.3 The most recent NHANES (NHANES IV: 2001–2002) indicated that the mean urine excretory level of iodine has stabilized since NHANES III.4