Iodine (I)

What is iodine?

Iodine is a mineral that is essential for growth and metabolism. It is often present in the form of iodide, so you may see the terms iodine and iodide used interchangeably. Since we cannot produce iodine in our bodies, we must get this mineral from food.

Why we need it

Iodine is needed to make two important hormones: thyroxine (T4) and triiodothyronine (T3). These are called thyroid hormones because they are made in the thyroid gland, a small organ located in the front of the neck.

T4 and T3 have many functions in the body. They help us regulate our basal metabolic rate (i.e., how fast we burn energy at rest) as well as our oxygen consumption and body heat.¹ Thyroid hormones are also critical for brain development, as they promote the development of brain cells through their effects on gene expression.¹

Where it’s found

Iodine is naturally found in many foods, including seafood, dairy, meat, and grains. Examples of iodine-rich foods include:

• Seaweed
• Milk
• Bread
• Cod
• Shrimp
• Yogurt
• Eggs
• Beef liver
• Oysters

Salt is another major source of iodine, as iodine is added into salt during processing. However, it’s important to check the label and look for “iodized salt”, since not all salt is fortified with iodine.

You can also get iodine from supplements. Iodine is available as a stand-alone supplement, and it is found in multivitamins and some prenatal supplements.²

Daily requirements

The daily Recommended Dietary Allowance (RDA) for iodine, or the amount that is likely to meet the needs of most healthy people, is 90 micrograms (mcg) for children aged 1-8 years, 120-150 mcg for adolescents aged 9-18 years, and 150 mcg for adults over the age of 19 years.³ For pregnant or breastfeeding women, the RDA increases to 220 mcg and 290 mcg, respectively.³

Iodine deficiency

Iodine deficiency can cause serious health issues. It can interfere with growth and development, especially in the brain. For example, iodine deficiency can cause stunted growth and cognitive deficits, which may be irreversible.⁴

Iodine deficiency can also cause goiter, a condition characterized by visible swelling of the thyroid gland. Additionally, iodine deficiency may lead to hypothyroidism, a condition characterized by very little thyroid activity. Symptoms of hypothyroidism include weight gain, fatigue, intolerance to cold, and dry skin.⁵

Fortunately, most people get enough iodine from their diet, so deficiency is relatively rare. Nonetheless, it is a concern for pregnant women, who require higher amounts of iodine to promote normal fetal growth and development.⁶

Can you get too much iodine?

Iodine can be toxic when consumed in excessive amounts. Iodine toxicity can cause hyperthyroidism, a condition involving thyroid overactivity. Symptoms of hyperthyroidism include weight loss, irregular heart beat, intolerance to heat, jitteriness, and swelling of the hands and feet.⁷ Iodine toxicity is typically caused by consuming excessive amounts of iodine-containing supplements or medications, although it may also be caused by getting too much iodine from food.⁸

To prevent toxicity, a Tolerable Upper Intake Level (UL) has been established for iodine. The UL for iodine is 1,100 mcg.³ This value represents the maximum daily amount of iodine that is unlikely to have adverse effects.

Fun facts

Not only is iodine crucial inside our bodies, but it is also used topically. Iodine can act as an antiseptic, which is a substance that is applied to the skin to fight infection. Iodine-containing antiseptics are often used during surgery preparation, as they promote healthy wound healing and help prevent infections at the surgical site.

Seaweed has the unique ability to absorb large amounts of iodine from seawater. Because of this, seaweed is perhaps the strongest dietary source of iodine. For reference, just 2 tablespoons of dried nori seaweed provides 116 mcg of iodine, which is about 77% of the RDA for adults.⁹

References

1. Cheng, S. Y., Leonard, J. L., & Davis, P. J. (2010). Molecular aspects of thyroid hormone actions. Endocrine reviews, 31(2), 139–170.
2. Office of Dietary Supplements, National Institutes of Health. (2021). Dietary Supplement Label Database. https://dsld.od.nih.gov/dsld/index.jsp
3. Institute of Medicine. (2001). Dietary Reference Intakes for Vitamin A, Vitamin K, Arsenic, Boron, Chromium, Copper, Iodine, Iron, Manganese, Molybdenum, Nickel, Silicon, Vanadium, and Zinc. DOI: 10.17226/10026
4. Toloza, F., Motahari, H., & Maraka, S. (2020). Consequences of Severe Iodine Deficiency in Pregnancy: Evidence in Humans. Frontiers in endocrinology, 11, 409.
5. Chaker, L., Bianco, A. C., Jonklaas, J., & Peeters, R. P. (2017). Hypothyroidism. Lancet (London, England), 390(10101), 1550–1562.
6. Niwattisaiwong, S., Burman, K. D., & Li-Ng, M. (2017). Iodine deficiency: Clinical implications. Cleveland Clinic journal of medicine, 84(3), 236–244.
7. Kravets I. (2016). Hyperthyroidism: Diagnosis and Treatment. American family physician, 93(5), 363–370.
8. Leung, A. M., & Braverman, L. E. (2014). Consequences of excess iodine. Nature reviews. Endocrinology, 10(3), 136–142.
9. USDA, FDA and ODS-NIH. (2022). Database for the Iodine Content of Common Foods

Food high in Iodine (I)

This list shows food that are top sources of Iodine (I) and the quantity of Iodine (I) in 100g of food