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Iodine during pregnancy: supplementation should not be systematic

Iodine-containing food supplements have no proven benefits for pregnant women, and can be dangerous for the unborn child.

Iodine plays a major role in thyroid function. Dietary intake of iodine is sometimes considered inadequate in Europe, but there are no high-quality data demonstrating the value of systematically recommending iodine supplementation for pregnant women who are eating a balanced diet.

Excessive iodine intake during pregnancy, before the fetus’s thyroid has fully matured, can cause hypothyroidism in the unborn child. The clinical consequences in affected children are hypothyroidism, goitre, impaired intellectual developmental and hearing loss.

The recommended iodine allowance is not very different from a dangerous level of intake.

It is advisable to check a pregnant woman’s iodine intake, including that from food supplements, seaweed, a poorly balanced diet, and certain drugs. Iodine is present in iodinated table salt, seafood, including seaweed and fish, and eggs and dairy products, especially when produced through conventional rather than organic farming.

Most of the multivitamin food supplements marketed for pregnant women and sold in community pharmacies deliver high iodine doses, sometimes higher than the recommended allowance. Some iodine food supplements sold without a prescription, especially over the internet, contain up to 50 times more iodine than the recommended daily allowance.

It is helpful to inform women of childbearing potential and women who are already pregnant that excessive doses of iodine-containing food supplements are dangerous for their unborn child. Systematic supplementation should be avoided, because sufficient daily iodine is provided by a balanced diet.

©Prescrire 1 June 2021

Source: "Excessive iodine intake during pregnancy: hypothyroidism in the unborn child" Prescrire International 2021; 30 (227): 154-156. Subscribers only.

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