Iodine Requirements and Dietary Sources

Fish on salt -- source of iodine
Evgeny Kuklev / Getty Images

Iodine is a trace mineral that your body needs to synthesize thyroid hormones called thyroxine (T4) and triiodothyronine (T3). These hormones are necessary for regulating your body's growth, development, metabolism, and body temperature. Iodine is especially important for fetal and infant development as they are the most sensitive to iodine deficiency.

Seventy to 80% of the iodine in your body is found in the thyroid gland in the neck, and the rest is found in the blood, muscles, ovaries and other parts of the body. And while the main functions have to do with thyroid hormones, iodine might also be important for breast health and normal immune system function.

The dietary reference intakes are set by the Health and Medicine Division of National Academies of Sciences, Engineering, and Medicine. The recommendations are based on age and represents the amount thought to be needed for a healthy person. Women who are pregnant or breastfeeding need more iodine. The daily value used for food labels and set by FDA recommends an intake of 140 micrograms of iodine per day.

Dietary Reference Intakes

1 to 8 years: 90 micrograms per day
9 to 13 years:
120 micrograms per day
14+ years:
150 micrograms per day
Women who are pregnant: 
220 micrograms per day
Women who are breastfeeding: 290 micrograms per day

The highest levels of iodine are found in seaweed such as kelp, nori, kombu and wakame. Iodine is also commonly found in seafood, iodized salt, and in lesser amounts in dairy products, fruits and vegetables. The iodine levels found in fruits and vegetable is dependent on how much iodine is in the soil. 

Iodine can be toxic in large amounts (approximately 1,000 micrograms per day). Ingesting too much iodine can depress thyroid gland function.

Iodine Deficiency

Deficiency can result in a thyroid condition called goiter. A hormone called thyroid-stimulating hormone increases the thyroid's ability to take up iodine and stimulates the synthesis and release of the thyroid hormones T3 and T4. A lack of iodine keeps the levels of thyroid-stimulating hormone too high and causes goiter. In infants, even a mild case of deficiency in the first trimester may lower IQ. About 40% of prenatal vitamins have iodine. 

Goiter was common in the middle regions of the United States in the early 20th century since the soil contained no iodine (plants grown on coastal regions contain small amounts of iodine from the soil). Adding iodine to table salt effectively wiped out iodine deficiency.

Iodine Toxicity

Excessive intake of iodine can cause similar symptoms as an iodine deficiency and hypothyroidism in some people.

The Institute of Medicine has set the tolerable upper limits of iodine intake at 1,100 micrograms per day for adults. The tolerable upper limit is the largest amount that's known to be safe for the average healthy person to take on a daily basis.

People with thyroid conditions may have lower tolerable upper limits and should speak with a doctor. If you have any health conditions, you should speak with your health care provider about your iodine intake.

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Article Sources
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  1. Iodine. Fact Sheet for Health Professionals. National Institutes of Health. Updated September 16, 2020

  2. Clinical Thyroidology for the Public. May 2019. Vol 12 Issue 5 p.3-4

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