This work aimed to assess the effect of iodine supplementation initiated in the preconception or the first trimester of pregnancy on the prevalence of iodine deficiency and maternal thyroid status in Portuguese women.
Iodine is an essential micronutrient to produce thyroid hormones, which regulate metabolism, growth, and development. Maternal iodine status is particularly important during the first trimester of pregnancy when the fetal thyroid status relies entirely on maternal iodine and thyroid function. Iodine deficiency is considered the most important preventable cause of brain impairment. Severe gestational iodine deficiency has been associated with detrimental and irreversible consequences for the offspring, including hypothyroidism and impaired brain development.
This study is an ongoing observation of pregnant and lactating women in Portugal. In 2013, health authorities in Portugal recommended iodine supplementation for women during preconception, throughout pregnancy, and during lactation.
However, this study points out that Portuguese pregnant women are still deficient in iodine after a decade of recommendation. Only 15% of pregnant women have adequate iodine status, some of them even with supplementation.
The median urinary iodine concentration (UIC) was significantly higher among women taking iodine supplements (100 µg/L vs. 63 µg/L), but it was still below the levels the World Health Organization recommended.
The World Health Organization (WHO) guidelines advise that pregnant and lactating women have an iodine intake of 250 µg/day. During pregnancy, a median urinary iodine concentration (UIC) between 150 and 249 µg/L defines a population with adequate iodine intake.
Only 15% of pregnant women had adequate iodine status, and 17% showed a UIC of less than 50 µg/L. Whether iodine supplementation was started during preconception or during the first trimester of gestation did not influence iodine deficiency.
In the first trimester of pregnancy, total thyroxine levels were lower in non-supplemented women, and fT3 levels were higher in non-supplemented women. Thyroglobulin levels were lower in women who started iodine supplementation during preconception compared to non-supplemented women and women who started iodine supplementation during gestation.
The widespread evidence of iodine deficiency in developed countries has forced medical societies in Europe and North America and health authorities in several countries, including Portugal, to recommend that all women during preconception, gestation, and lactation take a daily tablet containing at least 150 µg of iodine. In Portugal, the recommended daily dose of iodine supplementation in pregnant women is 150 to 200 µg. The data of the present study suggest that iodine supplementation during preconception and pregnancy failed to ensure iodine sufficiency. Other measures may be necessary, such as universal policies of iodized salt, which is not mandatory in Portugal.
Mild iodine deficiency is widespread in the European population. Salt iodization is mandatory in 30 countries and voluntary in 13 European Region Member States, plus Kosovo. Food businesses trading across borders in the European Region must comply with different salt iodization regulations in each country, increasing complexity in the supply chain. This has led to the use of non-iodized salt in commercial goods, which adds to iodine deficiency with pregnant and lactating women at special risk.
According to a report released by WHO/Europe and the Iodine Global Network (IGN), the increasing popularity and availability of plant-based alternatives to key sources of iodine, such as milk, dairy, and fish, is contributing to persistent and increased insufficient iodine intake in the WHO European Region.
Salt iodization remains the main strategy for ensuring adequate iodine intake in the European Region, but it is also affected by dietary and lifestyle changes.
This should all be taken into account while addressing the iodine status in pregnant and lactating women.
Study:
Maria Lopes-Pereira, Susana Roque, Sarai Isabel Machado, Tim I M Korevaar, Anna Quialheiro, Ana Machado, Laura Vilarinho, Margarida Correia-Neves, Maria Rosaria Galanti, Adriano A Bordalo, Patrício Costa, Joana Almeida Palha, Iodineminho Study: Iodine Supplementation and Prevalence of Iodine Deficiency In Pregnant Women, The Journal of Clinical Endocrinology & Metabolism, Volume 109, Issue 11, November 2024, Pages e2065–e2074, https://doi.org/10.1210/clinem/dgae041
