Iodine Intake Trends in United States Girls and Women between 2011 and 2020

BACKGROUND

Usual intakes of iodine in United States girls and women, including pregnant and lactating women have not been adequately studied. Adequate intake of iodine is critical for neurodevelopment of girls, thyroid functions, and reproductive health of women.

OBJECTIVES

This study aimed to examine the adequacy and trends of iodine intake of United States girls and women between 2011 and 2020.

METHODS

We mapped the sources of United States girls and women's iodine intake from the 29 food groups between 2011 and 2020 using United States Department of Agriculture's iodine data release 2. The total food intakes from 2 d of dietary recall of the United States National Health and Nutritional Examination Survey and estimated iodine concentrations of the food groups were used to calculate the usual iodine intakes of female participants. Trends of usual intakes, urinary iodine concentrations (UIC), and estimated intake adequacy were calculated.

RESULTS

Median usual intakes of iodine estimated from diet and supplements and UIC of United States girls and nonpregnant, nonlactating women declined between 2011 and 2020 in all 3 age groups: ≤14 y, 15-49 y old, and ≥50 y. Median usual intakes of iodine for pregnant and lactating United States women declined as well. Inadequacy levels of usual iodine intake were 9.9% for nonpregnant, nonlactating women of reproductive age 15-49 y old, 40.3% for lactating, and 10.2% for pregnant women in the 2017-2020 period. Intake insufficiencies estimated from UIC were 48.8%, 63.2%, and 31.3% for nonpregnant, nonlactating women of reproductive age 15-49 y old, pregnant and lactating women, respectively, in the 2017-2020 period. A significant decline in milk consumption might be one of the major contributors to the dietary iodine decline in United States women.

CONCLUSIONS

Iodine intake of United States girls and women were on the decline between 2011 and 2020 and the increased inadequacy of iodine intake deserves public health attention.

Iodine Intake From Diet and Supplements and Urinary Iodine Concentration in a Cohort of Pregnant Women in the United States

BACKGROUND

The DRI Estimated Average Requirement (EAR) in pregnancy for Iodine (I), an essential nutrient for fetal neurodevelopment, is 160 μg/d. Supplementation with 150 μg/d I/day is recommended during pregnancy, however, neither dietary intake or the combination of diet and supplement intake has been reported in US pregnant women.

OBJECTIVE

Determine iodine intake from diet and supplements and iodine status in pregnancy by urinary iodine concentration in a large cohort of pregnant women.

DESIGN

Pregnant women (n=750) completed the Diet History Questionnaire 2.0 from the National Institute of Cancer or multiple 24-hour recalls at baseline and identified their prenatal supplement(s). Dietary iodine intake was estimated using the USDA, FDA and ODS-NIH Database for the Iodine Content of Common Foods at enrollment, supplemental iodine intake throughout the study using content databases, and urinary iodine concentration (UIC) by the modified Sandell-Kolthoff reaction in samples collected between 14-20 weeks gestation (n=966).

RESULTS

The median intake of iodine from diet was 108.8 μg/d, and 63% (473/750) were below the Estimated Average Requirement (EAR). Furthermore, 65% (529/818) took a supplement containing iodine, however, only 32% (259/818) took ≥150 μg/d. Median intake increased to 188.5 μg/d with the inclusion of I from supplements, however , 41% (380/925) remained below the EAR even after supplementation suggesting inadequate intake in nearly half of the cohort. A similar 48% (467/966) had UIC ≤150 μg/L.

CONCLUSIONS

Assessment of iodine status by UIC and intake of iodine from diet and supplements support a high prevalence of iodine insufficiency during pregnancy in this large cohort of US women.

FOXE1 Polymorphism Interacts with Dietary Iodine Intake in Differentiated Thyroid Cancer Risk in the Cuban Population

BACKGROUND

The incidence of differentiated thyroid cancer (DTC) is low in Cuba, and the contribution of dietary factors to DTC in this population has not been investigated so far. The aim of this study was to evaluate the relationship between dietary iodine intake and DTC with regard to the interaction with environmental factors or some common single nucleotide polymorphisms (SNPs), based on a case-control study carried out in Cuba.

METHODS

A total of 203 cases and 212 controls from the general population were interviewed face-to-face using the dietary intake questionnaire and the photo booklet from the E3N cohort. A specific food composition table was constructed for this study. For each parameter studied, the odds ratio (OR) was stratified on age group and sex, and further adjusted for dietary energy, smoking status, ethnic group, level of education, number of pregnancies, and body surface area.

RESULTS

The risk of DTC was significantly reduced with increasing consumption of fish (p = 0.04), but no association between total dietary iodine intake and DTC risk was evident (p = 0.7). This lack of significant association was true whatever the age, the smoking status, the dietary selenium intake, and the ethnicity (p > 0.05). DTC risk was positively and strongly associated with the number of copies in the minor allele (A) for SNP rs965513 near FOXE1 among people who consumed less iodine than the median (p = 0.005).

CONCLUSION

Overall, the majority of the studied population had an optimal dietary iodine intake. DTC risk was inversely associated with high fish consumption. Furthermore, DTC risk was positively associated with the number of copies in the minor allele (A) of rs965513 among people who consumed less iodine than the median. Because these findings are based on post-diagnostic measures, studies with pre-diagnostic dietary iodine are needed for confirmation.