Iodine intake is associated with thyroid function in mild- to moderately iodine deficient pregnant women
Journal article, Peer reviewed
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Original versionAbel MH, Korevaar, Erlund I, Villanger GD, Caspersen IH, Arohonka, Alexander J, Meltzer HM, Brantsæter AL. Iodine intake is associated with thyroid function in mild- to moderately iodine deficient pregnant women. Thyroid. 2018;28(10):1359-1371 http://dx.doi.org/10.1089/thy.2018.0305
Background: Studies indicate that mild to moderate iodine deﬁciency in pregnancy may have a long-term negative impact on child neurodevelopment. These effects are likely mediated via changes in maternal thyroid function, since iodine is essential for the production of thyroid hormones. However, the impact of iodine availability on thyroid function during pregnancy and on thyroid function reference ranges are understudied. The aim of this study was to investigate the association between iodine intake and thyroid function during pregnancy. Design: In a population-based pregnancy cohort including 2910 pregnant women participating in The Norwegian Mother and Child Cohort Study, we explored cross sectional associations of maternal iodine intake measured (1) by a food frequency questionnaire and (2) as iodine concentration in a spot urine sample, with plasma thyroid hormones and antibodies. Results: Biological samples were collected in mean gestational week 18.5 (standard deviation 1.3) and diet was assessed in gestational week 22. Median iodine intake from food was 121lg/day (interquartile range 90, 160), and 40% reported use of iodine-containing supplements in pregnancy. Median urinary iodine concentration (UIC) was 59lg/L among those who did not use supplements and 98lg/L in the women reporting current use at the time of sampling, indicating mild to moderate iodine deﬁciency in both groups. Iodine intake as measured by the food frequency questionnaire was not associated with the outcome measures, while UIC was inversely associated with FT3 (p=0.002) and FT4 (p<0.001). Introduction of an iodine-containing supplement after gestational week 12 was associated with indications of lower thyroid hormone production (lower FT4, p=0.027, and nonsigniﬁcantly lower FT3, p=0.17). The 2.5th and 97.5th percentiles of TSH, FT4, and FT3 were not signiﬁcantly different by groups deﬁned by calculated iodine intake or by UIC. Conclusion: The results indicate that mild to moderate iodine deﬁciency affect thyroid function in pregnancy. However, the differences were small, suggesting that normal reference ranges can be determined based on data also from mildly iodine deﬁcient populations, but this needs to be further studied. Introducing an iodine-containing supplement might temporarily inhibit thyroid hormone production and/or release.
PublisherMary Ann Liebert
SeriesThyroid;Volume 28, Number 10, 2018
Except where otherwise noted, this item's license is described as © Marianne Hope Abel et al., 2018; Published by Mary Ann Liebert, Inc. This Open Access article is distributed under the terms of the Creative Commons Attribution Noncommercial License (http://creativecommons.org/licenses/by-nc/4.0/) which permits any noncommercial use, distribution, and reproduction in any medium, provided the original author(s) and the source are cited.