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Iodine is a trace mineral needed to make thyroid hormones, which are necessary for maintaining normal metabolism in all cells of the body.

Where is it found?

Seafood, iodized salt, and sea vegetables—for example, kelp—are high in iodine. Processed food may contain added iodized salt. Iodine is frequently found in dairy products. Vegetables grown in iodine-rich soil also contain this mineral.

Iodine has been used in connection with the following conditions (refer to the individual health concern for complete information):

Science Ratings Health Concerns

Childhood intelligence in newborns (if deficient)

Goiter (iodine deficiency-induced)


Attention deficit–hyperactivity disorder (to prevent ADHD in the children of pregnant women consuming an iodine-deficient diet)



Fibrocystic breast disease

3Stars Reliable and relatively consistent scientific data showing a substantial health benefit.
2Stars Contradictory, insufficient, or preliminary studies suggesting a health benefit or minimal health benefit.
1Star For an herb, supported by traditional use but minimal or no scientific evidence. For a supplement, little scientific support and/or minimal health benefit.

Who is likely to be deficient?

People who avoid dairy, seafood, processed food, and iodized salt can become deficient. Iodine deficiency can cause low thyroid function, goiter, and cretinism. Although iodine deficiencies are now uncommon in Western societies, the U.S. population has shown a trend of significantly decreasing iodine intake from 1988–1994.1 If this trend continues, iodine deficiency diseases may become more common.

How much is usually taken?

Since the introduction of iodized salt, iodine supplements are unnecessary and not recommended for most people. For strict vegetarians who avoid salt and sea vegetables, 150 mcg per day is commonly supplemented. This amount is adequate to prevent a deficiency and higher amounts are not necessary.

Are there any side effects or interactions?

High amounts (several milligrams per day) of iodine can interfere with normal thyroid function and should not be taken without consulting a doctor.2 Although potassium iodide supplementation (prescribed for some skin disorders) is usually well-tolerated, it has been known to produce adverse reactions such as rashes, itching or lesions on the skin, gastrointestinal symptoms, or hypothyroidism, especially in people with a prior history of thyroid problems.3 Because of such potential problems, the use of potassium iodide therapy should be supervised by a doctor. The average diet provides about four times the recommended amount of iodine. For susceptible people, that amount of iodine may be enough to cause health problems.4 A possible link to thyroid cancer has been observed in areas where an iodine-rich diet is consumed,5 6 and among populations that supplement with iodine.7 8 However, there is insufficient evidence to conclude that iodine supplementation is responsible for the increased incidence of thyroid cancer. Some people react to supplemental iodine, the first symptom of which is usually an acne-like rash.

When people with small, nontoxic goiter (living in areas not deficient in iodine) received iodine injections, they had a higher incidence of abnormal antibodies suggestive of the early stages of autoimmune thyroid disease.9

Children with iodine deficiency may also have iron-deficiency anemia, and this anemia may interfere with the therapeutic action of iodine supplementation.10 Correcting iron deficiency in such children with iron supplements has been shown to improve the efficacy of oral iodine in treating goiter.11

At the time of writing, there were no well-known drug interactions with iodine.


1. Hollowell JG, Staehling NW, Hannon WH, et al. Iodine nutrition in the United States. Trends and public health implications: iodine excretion data from National Health and Nutrition Examination Surveys I and III (1971–1974 and 1988–1994). J Clin Endocrinol Metab 1998;83:3104–8.

2. Mu L, Derun L, Chengyi Q, et al. Endemic goiter in central China caused by excessive iodine intake. Lancet 1987;2:257–9.

3. Heymann WR. Potassium iodide and the Wolff-Chaikoff effect: Relevance for the dermatologist. J Am Acad Dermatol. 2000 Mar;42:490–2.

4. Pennington JA. A review of iodine toxicity reports. J Am Diet Assoc 1990;90:1571–81.

5. Williams ED, Doniach I, Bjarnason O, et al. Thyroid cancer in an iodide rich area. Cancer 1977;39:215–22.

6. Kim JY, Kim KR. Dietary iodine intake and urinary iodine excretion in patients with thyroid diseases. Yonsei Med J. 2000;41:22–8.

7. Harach HR, Williams ED. Thyroid cancer and thyroiditis in the goitrous region of Salta, Argentina, before and after iodine prophylaxis. Clin Endocrinol (Oxf) 1995;43:701–6.

8. Harach HR, Escalante DA, Onativia A, et al. Thyroid carcinoma and thyroiditis in an endemic goitre region before and after iodine prophylaxis. Acta Endocrinol (Copenh) 1985;108:55–60.

9. Papanastasiou L, Alevizaki M, Piperingos G, et al. The effect of iodine administration on the development of thyroid autoimmunity in patients with nontoxic goiter. Thyroid 2000;10:493–7.

10. Zimmermann M, Adou P, Torresani T, et al. Persistence of goiter despite oral iodine supplementation in goitrous children with iron deficiency anemia in Cote d’Ivoire. Am J Clin Nutr 2000;71:88–93.

11. Zimmermann M, Adou P, Torresani T, et al. Iron supplementation in goitrous, iron-deficient children improves their response to oral iodized oil. Eur J Endocrinol 2000;142:217–23.

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