Iodine, Double-Edged Sword for Thyroid Patients

Multiple websites try to sell high dose iodine formulas to help the body create more thyroid hormone.  Indeed, iodine is essential for the creation of thyroid hormone in the body, but there are caveats one should know about iodine and situations where it may result in more harm than good.


The role of iodine

The image on the left is T4, which contains four iodine molecules (I), the image on left is the structure of T3 with only 3 iodine molecules.  T3 is the more active form of thyroid hormone.

When the thyroid gland is stimulated by TSH or thyroid stimulating hormone, the thyroid gland starts to pull out iodine molecules from the blood stream and starts to attach iodine to a ring structure.  T4 contains 4 iodine molecules, while T3 contains 3 iodine molecules.  When there is not enough iodine, there is not enough raw materials to make the thyroid hormone molecule. 

But does this mean that ingesting more iodine will stimulate the thyroid gland to make more hormone?

Iodine:  the double-edged sword
If someone is deficient in iodine, then by all means, this deficiency should be corrected with supplementation or food.  The recommended daily intake of iodine is 150micrograms/day for adult males and females;  220micrograms/day for pregnant women; 290 micrograms/day for women who are breast-feeding. 

The upper limit of iodine is 1,100micrograms per day.  Beyond this dose, one should be careful.  There is a medical phenomenon called the Wolff-Chaikoff Effect
where too much thyroid hormone suppresses the thyroid gland so it actually makes less thyroid hormone.  The gland sort of slows down or shut off.  In fact, giving iodine to someone who is hyperthyroid (or making too much thyroid hormone) was a medically accepted practice to suppress the thyroid gland.  So in fact, someone who takes iodine because they suspect that their thyroid gland is "sluggish" may end up making their thyroid function even more sluggish by taking too much iodine.