Iodine status in pregnant women in the National Children's Study and in U.S. women (15-44 years), National Health and Nutrition Examination Survey 2005-2010

Abstract

Background: This report presents iodine data from National Health and Nutrition Examination Survey (NHANES) and from a sample of pregnant women in the National Children's Study (NCS) Vanguard Study.

Methods: Urinary iodine (UI) was measured in a one third subsample of NHANES 2005-2006 and 2009-2010 participants and in all 2007-2008 participants age 6 years and older. These measurements are representative of the general U.S. population. UI was also measured in a convenience sample of 501 pregnant women enrolled in the NCS initial Vanguard Study from seven study sites across the United States.

Results: NHANES median UI concentration in 2009-2010 (144 μg/L) was significantly lower than in 2007-2008 (164 μg/L). Non-Hispanic blacks had the lowest UI concentrations (131 μg/L) compared with non-Hispanic whites or Hispanics (147 and 148 μg/L, respectively). The median for all pregnant women in NHANES 2005-2010 was less than adequate (129 μg/L), while third trimester women had UI concentrations that were adequate (median UI 172 μg/L). Third trimester women participating in the NCS similarly had an adequate level of iodine intake, with a median UI concentration of 167 μg/L. Furthermore, NCS median UI concentrations varied by geographic location.

Conclusions: Dairy, but not salt, seafood, or grain consumption, was significantly positively associated with median UI concentration in women of childbearing age. Pregnant women in their third trimester in the NHANES 2005-2010 had adequate median UI concentrations, but pregnant women in NHANES who were in their first or second trimesters had median UI concentrations that were less than adequate. Non-Hispanic black pregnant women from both the NHANES 2005-20010 and the NCS consistently had lower UI median concentrations than non-Hispanic whites or Hispanics.

FIG. 1.

Description of National Health and Nutrition Examination Survey (NHANES) and National Children's Study (NCS) population utilized for each of the different analyses in this investigation and the justification.

FIG. 2.

Median urinary iodine (UI, μg/L) by age category, NHANES 2009–2010, participants 6 years and older. The solid horizontal reference lines indicate the adequate iodine intake range defined by the World Health Organization (WHO; 100–199 μg/L) for the general population. The dashed horizontal reference lines indicate sufficient median iodine intake for pregnant women (150–249 μg/L).

FIG. 3.

Median UI (μg/L) for participants older than 6 years and women of childbearing age based on NHANES 2001–2010.

FIG. 4.

(A) Histogram of UI (μg/L) for pregnant women in NHANES 2007–2010 (n=76; reference line denotes the median UI=135.0 μg/L). (B) Histogram of UI (μg/L) for pregnant women (n=501) in the NCS (reference line denotes the median UI=166.9 μg/L). (C) Histogram of UI (μg/L) for pregnant non-Hispanic black women, NHANES 2007–2010 (n=14; reference line denotes the median UI=118.5 μg/L). (D) Histogram of UI (μg/L) for pregnant non-Hispanic black women (n=22) in the NCS (reference line denotes the median UI=133 μg/L).