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Iodine is a chemical element in the periodic table that has the symbol I and atomic number 53. It is required in trace amounts by most living organisms.

Just the facts

Physical Information

Name: Iodine

Use: essential element

Source: added to salt

Recommended daily intake: 150 micrograms of iodine per day for both men and women


Sensitive individuals:

Toxicity/symptoms: iodine deficiency gives rise to goiter

Regulatory facts:

General facts:



Chemical Structure

Chemical Description

Iodine is an essential trace element; its only known roles in biology are as constituents of the thyroid hormones, thyroxine (T4) and triiodothyronine (T3). These are made from addition condensation products of the amino acid tyrosine, and are stored prior to release in a protein-like molecule called thryroglobulin. T4 and T3 contain four and three atoms of iodine per molecule, respectively. The thyroid gland actively absorbs iodide ion from the blood to make and release these hormones into the blood, actions which are regulated by a second hormone TSH from the pituitary.

Health Effects

CDC commentary on iodine levels in the US is here. Median levels have fallen but seem to have stabilized.

Here is a summary from #Hollowell, et al:

The median urinary iodine level in the US frell from 32 microgm/dL in 1971-74 to 14.5 microgm/dL in 1988-94. The proportion of the population with UI concentrations below 5.0 microg/dL was 4.5 times higher in 1988-1994 than in 1971-1974, (P , 0.0001). This increase in the proportion of people with low levels was seen for all demographic categories and for all age groups. In 1988-1994, 8.1% of males and 15.1% of females had UI concentrations below 5 mg/dL. The highest prevalence of low concentrations was in the 40- to 49-yr-old age group (23.1% of women and 12.7% of men). Among white non-Hispanics, the percentage with UI concentrations below 5.0 microgm/dL was even higher in women of this age group (25.5%).

The percentage of women of child-bearing years (15-44 yr) with UI concentrations below 5 microgm/dL increased 3.8 times between the two study periods, and the percentage of pregnant women with UI concentrations below 5.0 mg/dL increased 6.9 times.

In estimating excessive iodine intake, 27.8% of the 1971-1974 population exceeded the UI concentration of 50 microgm/dL, and 5.3% exceeded 100 mg/dL. In 1988-1994, 5.3% of the population exceeded UI concentrations of 50 mg/dL, and 1.3% exceeded 100 mg/dL.

Current Events

CDC commentary on iodine levels in the US is at Median levels have fallen but seem to have stabilized.

One additional thought: In areas where drinking water is contaminated with perchlorate or nitrate, iodine uptake into the thyroid gland is decreased. Perchlorate (a drinking water contaminate from rocket fuel, fireworks mfg, etc) and nitrate (from fertilizer use and runoff from confined animal feedlot operations) interfere with the iodine transport system. Their effects on this system are additive.

In people who already have inadequate or low intake of iodine, exposure to nitrate or perchlorate would be expected to further raise the risk of inadequate thyroid hormone levels. Adequate maternal thyroid hormone is essential for normal fetal brain development and even subclinical hypothyroidism can have adverse effects. Full report in: #Haddow et al. New Engl J Med, 1999.


Iodine was discovered by Bernard Courtois in 1811. He was born to a manufacturer of saltpeter (potassium nitrate, a vital part of gunpowder). At the time France was at war, saltpeter, a component of gunpowder, was in great demand. Saltpeter produced from French niter beds required sodium carbonate, which could be isolated from seaweed washed up on the coasts of Normandy and Brittany.


Hollowell, Joseph G., Norman W. Staehling, W. Harry Hannon, Dana W. Flanders, Elaine W. Gunter, Glen F. Maberly, Lewis E. Braverman, Sam Pino, Dayton T. Miller, Paul L. Garbe, David M. DeLozier1 and Richard J. Jackson. "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}." The Journal of Clinical Endocrinology & Metabolism Vol. 83, No. 10 3401-3408.

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