U.S. Iodine Nutrition: Where Do We Stand?

Abstract

Surveillance of urinary iodine values of the U.S. population has been carried out at intervals since 1971. In this issue, Caldwell et al. (1) report on the most recent U.S. National Health and Nutrition Examination Survey (NHANES) iodine data, for the 2003–2004 sample. Reassuringly, there has been no significant change since the last NHANES survey in 2001–2002. Following a precipitous drop in urinary iodine values between NHANES I (1971–1974) and NHANES III (1988–1994), U.S. dietary iodine intake appears to have stabilized. Importantly, the U.S. population overall remains iodine sufficient. Spot urinary iodine values are used most frequently to screen for iodine deficiency in general populations. A limitation of urinary iodine testing is that identifying individuals at risk for iodine deficiency is not possible, as there is substantial diurnal and day-to-day variation in urinary iodine excretion (2,3). Urinary iodine concentration thresholds have only been identified for populations. In NHANES 2003–2004, 2.4% of all adults and 4.0% of women of childbearing age had urinary iodine concentrations 100mg=L are consistent with adequate iodine intake in lactating women (4). These values are lower than for pregnant women because some iodine is excreted in breast milk rather than in urine. NHANES does not provide any information about the iodine