At the 2024 Journées Francophones de la Nutrition, held in Strasbourg from December 4 to 6, experts gathered to explore the important topic of contaminants and their effects on the thyroid. Among the key topics was the essential role of maternal thyroid hormones in fetal brain development.
Maternal Thyroid Hormones
Maternal thyroid hormones are indispensable for proper brain maturation in the fetus, emphasized Jean-Baptiste Fini, PhD, a biologist at the French National Centre for Scientific Research. While severe iodine deficiency during pregnancy, which can cause cretinism, is no longer seen in France, even mild deficiencies can have profound effects on fetal development.
A cohort study highlighted the impact of insufficient maternal thyroid hormone levels. Children born to mothers with hypothyroxinemia, either before pregnancy or during the first trimester, were found to have lower IQ scores, reduced gray matter density, and smaller cortical volumes.
Placental Barrier and Contaminants
Fetal thyroid metabolism can be disrupted by contaminants transmitted through the mother’s diet, as the placental barrier does not entirely block certain harmful substances. Numerous studies have investigated the effects of in utero exposure to these contaminants on developmental disorders in children.
One epidemiological study identified a correlation between language delays in 30-month-old children and maternal exposure to specific chemicals, as measured in maternal blood and urine samples. Supporting this, experiments with tadpoles exposed to the same chemicals revealed impaired function in multiple genes involved in neural stem cell activity, with a significant reduction in their mobility.
Iodine Mitigates Contaminant Damage
Bernard Salles, DVM, PhD, a toxicologist at France’s National Research Institute for Agriculture, Food and Environment, highlighted that most European women consume iodine at levels below the World Health Organization’s recommended intake. Additionally, over 90% of women of childbearing age are exposed to thyroid-disrupting chemicals. Experimental studies in tadpoles demonstrated that exposure to a combination of 15 thyroid-disrupting contaminants, combined with iodine deficiency, altered the expression of hypothalamic and pituitary genes that regulate thyroid function. These disruptions were corrected with iodine supplementation.
If similar effects were proven in mammals, including humans, it would raise the need to consider routine urinary iodine testing in pregnant women during early pregnancy. More broadly, the widespread presence of dietary contaminants necessitates addressing the concept of exposomes and the combined effects of harmful substance “cocktails.”
Improving Regulatory Studies
In 2021, the French National Institute of Health and Medical Research (INSERM) published a comprehensive report on the health effects of pesticide exposure. Compared with the previous 2011 report, the 2021 findings linked additional pathologies, including thyroid disorders, to pesticide exposure, with a moderate level of presumed causation.
While no definitive causal links were established for pregnant women, newborns, or women highly exposed to pesticides (eg, those living near agricultural or industrial areas), occupational exposure to certain chemicals was associated with increased risks for hypothyroidism. These chemicals include organochlorine insecticides (such as chlordane), one herbicide, and one organophosphorus pesticide. Notably, chlordane exposure was linked to hypothyroidism in farmers’ wives.
Experimental toxicology studies are necessary to confirm these associations. In vivo research has shown that certain pesticides, such as organochlorines, organophosphates, carbamates, and pyrethroids, disrupt thyroxine synthesis.
Salles, who contributed to the INSERM report, criticized European pesticide regulations as insufficient for assessing toxicity. Regulatory studies, often supplied by manufacturers, are outdated and based on questionable methodologies. The primary flaw lies in the reliance on rodent models, as required by European regulations. Rodents are an inadequate model for assessing the effects of pesticides on human thyroid synthesis. Instead, amphibians provide a more accurate model. Furthermore, some regulatory findings conflict with data from endocrinological research.
Despite these challenges, some positive regulatory changes have been implemented. For example, recent requirements mandate the display of toxicity information on product packaging and labels via QR codes. Salles emphasized that advocacy by NGOs, political leaders, media, and consumer associations could help drive further regulatory improvements.
This article was translated fromUnivadis France using several editorial tools, including AI, as part of the process. Human editors reviewed this content before publication.
Source link : https://www.medscape.com/viewarticle/should-pregnant-women-be-supplemented-iodine-2025a100020p?src=rss
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Publish date : 2025-01-28 03:33:59
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