Iodine is an essential mineral the thyroid uses to make thyroid hormones. As a supplement, usually potassium iodide or kelp, it is used to cover low intake, especially before and during pregnancy; potassium iodide is also an FDA-approved drug to protect the thyroid in radiation emergencies.
Also known as: potassium iodide, kelp, sodium iodide.
ODS lists a Recommended Dietary Allowance of 150 mcg a day for adults, 220 mcg in pregnancy and 290 mcg while breastfeeding. The Tolerable Upper Intake Level for adults is 1,100 mcg a day from food and supplements. Many multivitamins contain 150 mcg, and ODS notes that many iodine-only supplements contain high amounts, sometimes above the upper limit.
It is sold in the US as a dietary supplement. Under the 1994 dietary supplement law (DSHEA), FDA does not approve dietary supplements before they are marketed, and the maker, not FDA, is responsible for safety and labeling. FDA has approved potassium iodide as a drug to block the thyroid from taking up radioactive iodine in a radiation emergency.
ODS says too much iodine can cause some of the same problems as too little, including goiter, high TSH and an underactive thyroid, and can also cause an overactive thyroid, thyroiditis and thyroid papillary cancer. People with autoimmune thyroid disease or iodine deficiency may react to amounts that are safe for most people. Seaweed such as kelp is one of the richest sources of iodine.
Interactions, per ODS: high doses of iodine with antithyroid drugs such as methimazole can add up and cause an underactive thyroid; potassium iodide with ACE inhibitors (such as lisinopril) or potassium-sparing diuretics (such as spironolactone) can raise blood potassium. The American Thyroid Association recommends that women planning a pregnancy, pregnant or breastfeeding take 150 mcg a day of iodine as potassium iodide. If you have a thyroid condition or take thyroid medicine, ask your clinician before taking iodine.
We could not find a single published half-life or time to peak for iodine that applies to a supplement dose, so we do not list one. ODS says people absorb potassium iodide almost completely (96.4% in a small study), and the thyroid traps what it needs.
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