Q. I heard that if you ingest too much iodine, you can develop hypothyroidism. Is that true? I’m a little confused about why that would happen .

A. Yes – it is true that too much iodine can lead to hypothyroidism. It seems counterintuitive; you’d think that more iodine would lead to more thyroid hormone production. However, it does seem that there is a link between excessive iodine intake and autoimmune thyroid disease (leading to hypothyroidism).Recently, researchers from China have found that too much iodine leads to an influx of lymphocytes, for some reason, and an increased incidence of self attack on the thyroid:

“…although iodine supplementation should be implemented to prevent and treat iodine-deficiency disorders, supplementation should be maintained at a safe level. Levels that are more than adequate (median urinary iodine excretion, 200 to 299 µg per liter) or excessive (median urinary iodine excretion, >300 µg per liter) do not appear to be safe, especially for susceptible populations with either potential autoimmune thyroid diseases or iodine deficiency. Supplementation programs should be tailored to the particular region. No iodine supplementation should be provided for regions in which iodine intake is sufficient, whereas salt in regions in which iodine intake is deficient should be supplemented with iodine according to the degree of iodine deficiency.”

The underlying mechanism hasn’t been entirely worked out – but there does seem to be a link. So: adequate (but not excessive) iodine supplementation is important in iodine-deficient regions, whereas people in iodine-rich regions should not ingest additional iodine.



7 Responses to Can too much iodine cause hypothyroidism?

  1. Balyhoo says:

    Interesting question and great answer. Wonder if I could even dream up a question to stump this Professor. 🙂 Oh, and thanks for the Birthday wishes. 😉

  2. Elena Guce says:

    nope too much iodine can lead to HYPERTHYROIDISM not hypothyroidism, you can research it on google or even in yahoo…

  3. admin says:

    Sure, it can lead to hyperthyroidism – but recent research shows that it may also lead to hypothyroidism. Check out this article from the New England Journal of Medicine: Teng W et al. Effect of iodine intake on thyroid diseases in China. NEJM 2006; 354:2783-2793. From the first paragraph:

    “We observed an increase in the prevalence of overt hypothyroidism, subclinical hypothyroidism, and autoimmune thyroiditis with increasing iodine intake in China…”

  4. vasi says:

    I agree that too much iodine can sometimes lead to hypothyroidism, but in most cases it leads to hyperthyroidism (see iodine induced hyperthyroidism or Jod-Basedow phenomenon), especialy in iodine deficient areas.

  5. admin says:

    Yes – you’re absolutely right! Too much iodine can definitely lead to hyperthyroidism – particularly if you give someone who’s been iodine deficient (and thus has a goiter) some iodine (the Jod-Basedow phenomenon). Dangerous.

  6. DS says:

    I believe this article. I used to eat idodine rich foods addictively for years then stopped. Within a year or two, I was diagnosed with Hypothyroidism. Going on my third year on tablets..
    I always used to find it hard to agree when people accused me on not having sufficient Iodine intake, but now I understand the reason for my thyroid condition..

  7. GOAT says:

    Yes, it is possible, it is known as Wolff-Chaikoff phenomenon, where large quantities of iodine ingestion triggers a counter-regulatory effect in the thyroid gland leading to hypothyroidism. It last for about 3 days, then an ‘escape phenomenon’ occur to normalize the thyroid hormone level.

    Source: Markou K.Iodine-induced Hypothyroidism. Thyroid.2001

Leave a Reply

Your email address will not be published. Required fields are marked *