The iodine status of Americans has changed significantly over the past 20 years, according to a Centers for Disease Control and Prevention (CDC) study published in October’s Journal of Clinical Endocrinology and Metabolism. While there were concerns in the 1970’s and 1980’s about possible high iodine intake, a laboratory indicator of iodine intake more recently shows that median urinary iodine concentrations have decreased by more than half, from 32 to 14.5 micrograms per deciliter.
The study, “Iodine Nutrition in the United States: Trends and Implications,” based on CDC’s National Health and Nutrition Examination Surveys (NHANES), found in a 1988-1994 sample of the U.S. population that nearly 12 percent of Americans had low urine iodine concentrations, an increase from three percent of the population in 1974. The World Health Organization (WHO) defines iodine deficiency as a public health problem when levels this low are found in 20 percent or more of the population.
Iodine is a crucial nutrient for production of thyroid hormone, which plays an essential role in brain development, metabolism, and other bodily functions. Proper iodine intake is a difficult balance, because excessive iodine can also cause health disorders.
Iodine intakes should be closely monitored to determine whether this decrease is a “one-time drop or a continuing process,” said Dr. Joseph Hollowell of CDC’s National Center for Environmental Health. He indicated that iodine excretion and dietary intake should be routinely measured in health and dietary surveys of the population as part of an early warning system to prevent reemergence of either deficiency or toxicity in the United States.
“Lack of iodine is the world’s leading cause of preventable mental retardation and can cause population-wide drops in IQ in areas where deficiency is common,” said Dr. Glen Maberly of Emory University’s Rollins School of Public Health. “It is important to monitor this balance.”
In the United States, the use of iodized table salt has been the major public health approach to controlling iodine deficiency. “For the last 50 years, physicians in the United States have seen little or no iodine deficiency; however, we cannot assume that it can no longer happen here,” said Dr. Richard Jackson, director of CDC’s National Center for Environmental Health. The recent increase in prevalence of iodine deficiency in Europe has prompted public health officials there to increase the iodine level of salt and to improve monitoring.