Iodine Inadequacy Is Prevalent and Has Continuously Increased from 2001 to 2018 in the United States

There have been continuous changes in the production, processing and consumption of major sources of iodine in the diet, especially iodized salt, dairy, and bread, that have reduced iodine intake in the United States.

The aim of this study was to assess iodine status and trends over 18 y in United States adults and adolescents, with emphasis on vulnerable groups, including women of reproductive age (WRA), pregnant females, and specific ethnic groups.

Urinary iodine-to-creatinine ratio (UI/Cr), a standard method for evaluating population iodine status, was assessed using NHANES data collected in 2001-2018 on individuals aged 14+ y (n = 22,851). Median values and the percentage less than the estimated average requirement (EAR) from 2001 to 2002 were compared with 2017 to 2018 values. Trends from 2001 to 2018 were examined with linear regression. Inadequate iodine status was estimated by determining population proportions below EAR.

In 2017-2018, 35% of WRA and 46% of pregnant females had inadequate intakes based on not meeting the EAR. For the same time period, 2017-2018, 44% of non-Hispanic Black, 32% Mexican American, and 25% other Hispanic females aged ≥14 y had inadequate intakes. Twenty-four percent of females aged ≥14 y had inadequate intakes in 2017-2018 compared with 12% in 2001-2002 (P < 0.001). Thirty percent of males aged ≥14 y had inadequate intakes in 2017-2018 compared with 17% in 2001-2002 (P < 0.001). Time trend analysis found linear decreases (P < 0.05) in median UI/Cr levels for females and males aged ≥14 y and ≥19 y.

In the total United States population aged >14+ y, the prevalence of individuals with intake below the EAR for iodine nearly doubled from 2001 to 2018. Substantial proportions of individuals in vulnerable groups, WRA, pregnant females, and minority females do not meet the iodine EAR. Given the current state of iodine nutriture and the likelihood of continuing decreases in iodine intake in the United States, effective educational and regulatory measures seem essential, especially to protect pregnant and minority females and their offspring.