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):
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, goitre, 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.
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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,
gastro-intestinal 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
When people with small, nontoxic goitre (living in areas not deficient in iodine) received
iodine injections, they had a higher incidence of abnormal antibodies suggestive of the early
stages of auto-immune thyroid disease.9
Children with iodine deficiency may also have
iron-deficiency anaemia, and this anaemia 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
At the time of writing, there were no well-known drug interactions
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
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
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
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The information presented in Aisle7 is for informational purposes only.
It is based on scientific studies (human, animal, or in vitro), clinical experience,
or traditional usage as cited in each article. The results reported may not necessarily occur
in all individuals. For many of the conditions discussed, treatment with prescription or over
the counter medication is also available. Consult your doctor, practitioner, and/or chemist
for any health problem and before using any supplements or before making any changes in