Excessive iodine intake during pregnancy can damage the placenta even if the mother thyroid levels remain perfectly healthy.
April 25, 2026
Original Paper
Excess Gestational Iodine Exposure Induces Trophoblast Dysfunction and Placental Immune Activation Independent of Thyroid Dysfunction
SSRN · 6633473
The Takeaway
Doctors have long assumed that iodine only affects fetal growth by changing the amount of thyroid hormone in the mother body. This study found that high levels of iodine cause direct inflammation and immune activation in the placenta itself. This damage leads to restricted fetal growth regardless of how well the thyroid is functioning. The finding proves that the placenta has its own specific sensitivity to iodine that was previously overlooked. It suggests that prenatal supplement guidelines may need to be adjusted to prevent direct placental toxicity. A healthy thyroid is no longer a guarantee that iodine levels are safe for the fetus.
From the abstract
Background: Iodine is essential for thyroid hormone synthesis, but excessive intake is increasingly common in iodine-replete populations, especially with seaweed-rich diets. Whether iodine excess has clinically relevant effects beyond maternal thyroid function remains uncertain.<br><br>Methods: We analyzed 416 pregnant women and 539 neonates from a prospective cohort, integrating placental histopathology, bulk and single-nucleus transcriptomics, trophoblast functional assays, and a rat model.<br