Why optimizing your iodine intake is so crucial, and why both too little and too much iodine can be harmful.
Iodine deficiency is the most common cause of hypothyroidism worldwide. Once researchers realized this, health authorities around the world began adding iodine to table salt.
This strategy was effective in correcting iodine deficiency. But it had an unanticipated—and undesired—effect. In countries where iodine has been added to table salt, the rates of autoimmune thyroid disease have risen.
Why does this happen? Because increased iodine intake, especially in supplement form, can increase the autoimmune attack on the thyroid. Iodine reduces the activity of an enzyme called thyroid peroxidase (TPO). TPO is required for proper thyroid hormone production.
On the other hand, restricting intake of iodine can reverse hypothyroidism. In one study, 78% of patients with Hashimoto’s regained normal thyroid function with iodine restriction alone.
However—and this is a big “however”— it appears that iodine may only pose a problem for people with Hashimoto’s and other autoimmune thyroid diseases in the presence of concurrent selenium deficiency. In the study above where rats developed goiter while receiving excess iodine, when they were given adequate selenium they did not develop the goiter.
Other studies have shown that selenium protects against the effects of iodine toxicity and prevents the triggering and flaring of autoimmune disease that excess iodine without selenium can cause.
Always test for both iodine deficiency and Hashimoto’s when a patient presents with hypothyroid symptoms. If they are iodine deficient, start them on a trial of iodine and selenium together. In most cases, patients see a significant improvement. In a minority of cases, they cannot tolerate supplemental iodine even with adequate selenium intake.
Unfortunately, the blood test for iodine that your doctor might run is not very accurate. The best way to determine iodine status is with a 24-hour urine loading test. This involves taking a large dose of iodine and collecting your urine for 24 hours afterward. If you are iodine deficient, you’ll retain more of the ingested iodine than you should and the level of iodine excreted in the urine will be lower than expected.
If your doctor or health care practitioner won’t order these tests, you can simply begin an iodine protocol. This involves starting with a low dose of iodine ( start with kelp tablets that contain 325 mcg of iodine per tablet) and increasing very slowly over time. It’s crucial that you also take 200 mcg of selenium per day during this protocol to protect against the potentially adverse effects of iodine supplementation, especially if you have autoimmune thyroid disease.
Physicians that specialize in treating hypothyroidism with iodine suggest doses as high as 50 mg per day may be necessary to restore iodine levels in those that are deficient. It’s imperative that patients build up to such high doses very slowly, and I don’t recommend doing it without the supervision of a clinician experienced with iodine treatment. Be aware that high doses of iodine can lead to a transient increase in TSH levels, which can be mistakenly interpreted as a sign of hypothyroidism.
Finally, it’s important to keep in mind that a minority of patients with Hashimoto’s confirmed by biopsy (the gold standard) never test positive for thyroid antibodies. This is probably because their immune systems are so depressed they can no longer produce antibodies. If you have a combination of hyper- and hypothyroid symptoms, I would still suspect Hashimoto’s even if your thyroid antibody tests are normal. It’s wise to be cautious with iodine if you have any signs of autoimmune thyroid disease, even without a confirmed diagnosis.
How much Iodine per day
| Life Stage | Recommended Amount |
|---|---|
| Birth to 6 months | 110 mcg |
| Infants 7–12 months | 130 mcg |
| Children 1–8 years | 90 mcg |
| Children 9–13 years | 120 mcg |
| Teens 14–18 years | 150 mcg |
| Adults | 150 mcg |
| Pregnant teens and women | 220 mcg |
| Breastfeeding teens and women | 290 mcg |
How much is too much
| Life Stage | Upper Limit |
|---|---|
| Birth to 12 months: | Not established |
| Children 1–3 years: | 200 mcg |
| Children 4–8 years: | 300 mcg |
| Children 9–13 years: | 600 mcg |
| Teens 14–18 years: | 900 mcg |
| Adults: | 1,100 mcg |