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High intakes of iodine among women during pregnancy and the postpartum period has no adverse effect on thyroid function

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Given the high consumption of seaweed soup by pregnant and lactating Korean women, concerns have been raised about excessive iodine intake. We evaluated the effects of maternal iodine intake on maternal thyroid function and birth outcomes. We also evaluated iodine intake via seaweed soup during late pregnancy and the early postpartum period.


A total of 349 pregnant women of the Ideal Breast Milk cohort were recruited in late pregnancy, of whom 302 revisited after delivery. Three-day dietary records were assessed at each visit. Blood was collected for thyroid function test. Obstetrical and birth outcomes were obtained.


The median dietary iodine intake was 459 μg/day (interquartile range [IQR] 326.5–647.4 μg/day) during pregnancy. Dietary iodine intake by quartile was not significantly associated with maternal thyroid status, or obstetrical or neonatal outcomes. However, the dietary iodine intake in the early postpartum period was 1759 μg/day (IQR 1026.7–2491.1 μg/day) because of a marked increase in seaweed soup consumption. Of all women, 25.8% consumed seaweed soup more than once over the 3 days of dietary records when pregnant, but the figure rose to 93.4% postpartum. Of postpartum women who consumed seaweed soup daily, the median dietary iodine intakes were 1355, 2394, and 3063 μg/day (soup at one, two, and three-or-four meals).


In these iodine-replete pregnant women, dietary iodine intake during pregnancy showed no effect on maternal thyroid function or birth outcomes. However, iodine intake in the early postpartum period was markedly increased by the frequency of seaweed soup consumption.

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Data availability

Due to the nature of this research, participants of this study did not agree for their data to be shared publicly, data described in the manuscript, code book, and analytic code will not be made available.


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We thank the pregnant women who participated in IBM study. We also acknowledge all the teams and staff who assisted in recruiting participants for this study.


This work was supported by the Korean Thyroid Association Young Investigator Award 2019. This work was supported by the Seoul National University Hospital Research Fund (30-2017-0070 and 04-2017-3010).

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Authors and Affiliations



YAL, SWC, DLJ, GJC, YJP, CHS, SKP, JKJ, JKC, and YJS: made contribution to the conception and design of the study. YAL, SWC, DLJ, CWC, YJP, CHS, SKP, JKC, and YJS: conducted research. YAL, SWC, and GJC: provided essential reagents or materials. YAL, SWC, DLJ, CWC, YJP, CHS, SKP, JKC, and YJS: analyzed data or performed statistical analysis. DLJ, SWC, CWC, and YJS: wrote and revised the article. All authors approved the final versions.

Corresponding authors

Correspondence to Sue K. Park or YoonJu Song.

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Conflict of interest

The authors declare that they have no potential conflicts of interest.

Ethical approval

This study was performed in line with the principles of the Declaration of Helsinki. The Ethics Committee of Seoul National University Hospital approved the study (IRB approval nos. 1512-039-727 for the mothers, 1606-117-772 for the children).

Consent to participate

All participants provided written informed consent after we carefully explained the purpose of the study.

Supplementary Information

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Ju, D.L., Cho, S.W., Chung, C.W. et al. High intakes of iodine among women during pregnancy and the postpartum period has no adverse effect on thyroid function. Eur J Nutr 62, 239–249 (2023).

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