Is an iodine-rich diet helpful or harmful to the thyroid?

The topic of iodine and thyroid health isn’t a new one. For years we’ve heard conflicting information about whether iodine is harmful to the thyroid gland or essential for thyroid function, and most of us are downright confused about what we should do (for good reason!). Should we avoid iodine altogether, limit our intake, or consume more iodine to support thyroid function? 

The answer, for many thyroid patients, is somewhere in the middle. We need some iodine to prevent an iodine deficiency, but not too much of it or we risk iodine toxicity. Being deficient in iodine can be harmful, but so can iodine excess. 

To clear up this confusion and help you discern whether to increase or limit your iodine intake, this blog post discusses the link between thyroid antibodies, iodine, and hypothyroidism. Keep reading to discover whether an iodine-rich diet is essential or detrimental to the thyroid gland.  

Thyroid function, iodine, and hypothyroidism

Let’s start things off by looking at why the thyroid gland needs iodine to function optimally. Not massive amounts of iodine, necessarily, but about 150 micrograms (mcg) daily in adulthood, 220 mcg during pregnancy, and 290 mcg during lactation — according to the National Institutes of Health (NIH). 

What is iodine and why do we need enough of it?

As an essential trace mineral that’s needed to produce thyroid hormones, too little iodine can prevent the thyroid gland from synthesizing the hormones it needs to do its job — contributing to an underactive thyroid gland (hypothyroidism), and potentially a goitre (an enlarged thyroid gland). In fact, iodine deficiency is the leading cause of hypothyroidism worldwide — especially in areas where marine foods aren’t consumed and iodized salt isn’t available. 

This is because the thyroid gland uses iodine to synthesize the thyroid hormone thyroxine (T4), which then needs to be converted to triiodothyronine (T3), its bioactive form. If T4 isn’t adequately produced, the pituitary gland increases its production of thyroid-stimulating hormone (TSH). This usually happens when less than 100 mcg of iodine is consumed daily. However, iodine intake typically needs to fall below 10 to 20 mcg daily for hypothyroidism to develop.

How much iodine is needed for thyroid health? 

So, how much iodine is needed to avoid becoming deficient in iodine and developing thyroid issues? This is where things get confusing. 

We need at least 100 mcg daily to prevent elevated TSH levels, but for optimal thyroid function, the NIH recommends getting 150 mcg daily (remember, pregnant and breastfeeding women need more). We just want to avoid getting too much iodine, as iodine excess is associated with hypothyroidism, elevated TSH, goitre development, and Hashimoto’s disease. Even the American Thyroid Association (ATA) warns against supplementing with more than 500 mcg of iodine daily (from kelp or iodine supplements). 

The link between iodine and Hashimoto’s disease

Now that we’ve looked at the link between iodine and hypothyroidism, let’s look at iodine and Hashimoto’s (autoimmune thyroiditis). Too little iodine can cause hypothyroidism, while too much can cause or worsen Hashimoto’s disease (a leading cause of hypothyroidism in iodine-sufficient parts of the world). 

So while iodine is essential for thyroid function, too much of it — especially from iodine supplementation — can increase thyroid peroxidase (TPO) antibodies and worsen Hashimoto’s symptoms. About 90 percent of Hashimoto’s patients already have elevated TPO antibodies, and further increases in these antibodies are something we don’t want!

Iodine and Hashimoto’s antibodies

As world-renowned Hashimoto’s expert, Dr. Datis Kharrazian explains in his article on iodine and Hashimoto’s disease, iodine stimulates TPO antibodies. In those with Hashimoto’s thyroiditis, this can increase the autoimmune attack on the thyroid gland and lead to worsened symptoms. It can also trigger Hashimoto’s to develop in those with increased intestinal permeability and a genetic predisposition for autoimmunity. 

For these reasons, Dr. Kharrazian warns against supplementing with iodine in the case of Hashimoto’s. He also recommends avoiding an iodine-rich diet that includes a lot of fish, seafood, seaweed, and iodized salt. 

Hashimoto’s and a low-iodine diet

Like Dr. Kharrazian, other functional and naturopathic medical practitioners such as Dr. Michael Ruscio believe that following a low-iodine diet can often be beneficial for those with Hashimoto’s. While iodine shouldn’t be avoided altogether, avoiding iodine-containing supplements and iodine-rich foods can benefit those with autoimmune thyroid disease. 

That said, there are some exceptions to following a low-iodine diet. For instance, low-iodine diets are not recommended for pregnant and breastfeeding women, children, and those who are strictly vegetarian or vegan. These populations shouldn’t reduce their iodine intake, and iodine supplementation may sometimes be necessary. However, an iodine urine test is recommended before supplementing. 

So, is an iodine-rich diet helpful or harmful? 

Whether to eat a high or low-iodine diet really comes down to two things: whether you have Hashimoto’s or an increased susceptibility to developing Hashimoto’s disease. Iodine is essential for thyroid hormone production and thyroid function, but too much of it can cause hypothyroidism, stimulate the production of TPO antibodies, and trigger Hashimoto’s thyroiditis. 

For most people without Hasimoto’s disease, it’s likely safe to consume between 150 and 450 mcg of iodine daily from food and/or supplementation. Those with Hashimoto’s; however, may want to stay closer to the lower end of the range and avoid taking iodine supplements.

If you’re still confused about whether to increase or limit your iodine intake, please don’t hesitate to reach out to me. As an experienced thyroid nutritionist, I offer personalized dietary, lifestyle, and supplement recommendations; functional nutrition testing (including an iodine urine test); and 10 per cent off all supplements purchased within my online dispensary. Book your free health review to begin!

Interested in a personalized approach? Schedule a free 20-minute inquiry call today and take the first step toward better health.