Food is medicine: The science behind iodine

Key takeaways:

• For those with insufficient iodine levels, supplements may be beneficial for proper fetal and infant neurodevelopment.
• Seaweed, seafood, eggs and iodized salt are popular dietary sources of iodine.

Iodine supplementation may have some benefits for expectant mothers and their children, but evidence is limited, according to experts.

Iodine, an essential mineral, is “a vital component of the thyroid hormones, thyroxine and triiodothyronine,” Edwina Wambogo, PhD, MPH, RD, a nutritional epidemiologist at NIH’s Office of Dietary Supplements (ODS), told Healio.

“Thyroid hormones regulate many physiological processes, including fetal and infant skeletal and central nervous system development,” she said.

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Jaime Gahche, PhD, MPH, director of the Population Studies Program at ODS, said seafood and eggs are good sources of iodine, but “seaweed is one of the best.”

“Dairy products also contain iodine, although the amount can vary depending on whether the cows received iodine feed supplements and whether iodophor sanitizing agents were used in the milk processing,” she said.

For patients aged 14 years and older, the recommended dietary allowance (RDA) for iodine is 150 µg per day, Gahche said. But during pregnancy, the RDA rises to 220 µg, and during lactation, it rises again to 290 µg.

Alongside many who are pregnant or lactating, Wambogo said patients who follow a vegan diet “might obtain insufficient amounts of iodine,” but dietary supplements can help increase intake to the recommended amount. For those who may obtain insufficient amounts from their diet, supplementation can ensure sufficient intake for fetal and infant neurodevelopment.

Summary of evidence

Research on the benefits of iodine supplementation is mostly unclear or insufficient to draw any definitive conclusions.

For example, in a 2020 systematic review and meta-analysis of 37 articles, researchers wrote that most studies suggested iodine supplementation had no impact on maternal or infant thyroid-stimulating hormone and free thyroxine, so there was not enough evidence to support recommendations for iodine supplementation during pregnancy.

Additionally, a 2013 systematic review of 14 articles including roughly 16,880 participants revealed that iodine during pregnancy or periconceptional period in regions of severe deficiency had inconsistent effects on thyroid function. However, it effectively reduced the risk for cretinism and improved only some motor function among children. Still, the researchers wrote that there was insufficient evidence on the impacts prenatal or periconceptional iodine supplementation has on children’s growth and cognitive function.

Other research has indicated iodine could have benefits if taken early on in pregnancy.

In a 2023 systematic review and meta-analysis of 11 studies containing 5,859 participants, researchers found that iodine helped participants reach adequate intake levels during pregnancy, and the best time to start supplementation was pre-pregnancy or in the first trimester. The daily supplement was beneficial for iodine status and maternal thyroid hormone concentrations, they wrote.

Additionally, a 2021 systematic review of four randomized clinical trials and four cohort studies that included roughly 82,430 participants revealed that for children who have mild-to-moderate iodine deficiency, daily supplementation can improve psychomotor development. Although the supplement seemed to improve gross motor skills, there was no significant improvement in children’s behavioral or mental development, the researchers wrote.

More information

Like most supplements, Wambogo said excessive intake can cause issues. Specifically, it hinders thyroid hormone synthesis, which results in thyroid growth, higher thyroid-stimulating hormone concentrations and goiter. Extreme intake is rare, she said, but can lead to diarrhea, abdominal pain, nausea, vomiting, weak pulse and even coma.

For those aged 19 years and older, iodine has a tolerable upper intake level (UL) of 1,100 µg per day.

“The UL refers to intakes from all sources — food, beverages and dietary supplements — though most people are unlikely to exceed the UL from foods and beverages alone,” Wambogo said.

Gahche noted that iodized salt may help ensure adequate intake, but “specialty salts like sea salt and Himalayan salt usually do not contain iodine.”

“Food manufacturers almost always use noniodized salt in processed foods, so consuming processed foods that contain salt does not substantially increase iodine intake,” Gahche said. “From a sodium perspective, most salt intake in the U.S. population comes from processed foods, so people can still limit sodium by cutting back on processed foods or choosing lower sodium options without substantially affecting their iodine intake.”

The Office of Dietary Supplements offers resources for health care providers and consumers. To learn more about iodine and other supplements, check out the Office of Dietary Supplements Fact Sheets.

Editor’s Note: Healio is highlighting the clinical value of various supplements. See other installments of the series here:

• Melatonin
• Omega-3
• Zinc and other supplements for immune function
• Vitamin D
• Calcium
• Ashwagandha
• Magnesium
• Folic acid
• Vitamin B12

References:

• Candido AC, et al. J Trace Elem Med Bio. 2023;doi:10.1016/j.jtemb.2023.127275.
• Dineva M, et al. Am J Clin Nutr. 2020;doi:10.1093/ajcn/nqaa071.
• Machamba AAL, et al. Arch Endocrinol Metab. 2021;doi:10.20945/2359-3997000000376.
• Zhou SJ et al. Am J Clin Nutr. 2013;doi:10.3945/ajcn.113.065854.