sea kelp

Q. When my internist noted a low-normal thyroid value, he suggested a thyroid supplement. I suspected I had an iodine deficiency from years on a low-salt diet. I proposed a trial of sea kelp and he agreed. Two 100 mg tablets a day brought up the thyroid value to normal and warmed my cold toes. I also noted my foot fungus receded 90 percent.

A. Using iodine to treat an underactive thyroid gland is controversial. Very few Americans get too little iodine, though your years of avoiding iodized salt may have resulted in an inadequate iodine intake for you.

In a case report, a woman who used kelp as an iodine supplement aggravated her thyroid disease.  German researchers noted that this woman developed thyrotoxicosis (aka hyperthyroidism) after consuming a kelp-containing tea (Journal of General Internal Medicine, June 2006). The following details have some doctorspeak, but is worth wading through as a cautionary tale:

We report a case of iodine-induced hyperthyroidism due to the ingestion of a kelp-containing tea. A 39-year-old woman with multinodular goiter presented with typical signs of hyperthyroidism…including tachycardia (100 beats/min), palpitations, tremor, nervousness, insomnia, fatigue, increased sweating, diarrhea, secondary amenorrhoea, and weight loss. Laboratory analysis revealed increased levels of fT3 and fT4 as well as a suppressed TSH concentration, anti-thyroid antibodies remained negative…

Considering the average iodine content of kelp of 1,500 to 2,500 μg/g, our patient was taking an estimated 580 to 990 μg iodine daily, i.e., 3.8 to 6.6 times the recommended daily allowance of 150 μg. For comparison, in the United States the estimated average iodine intake of men and women aged 25 to 30 years is 410 and 260 μg/day, respectively. In the literature, several cases of iodine-induced hyperthyroidism after consumption of seaweed have been described, this occurred mainly while taking kelp tablets…

In our patient, hyperthyroidism did not resolve spontaneously following discontinuation of the kelp-containing tea, as described previously, 20, 23 but required antithyroid drug therapy.”

Hyperthyroidism is a serious condition that can be challenging to treat. Here is a more recent case report of hyperthyroidism triggered by kelp. It was published in BMJ Case Reports (Oct., 2014):

“Complementary medications and herbal medicine for weight loss have become very popular. We report a case of thyroid dysfunction following the ingestion of a kelp-containing marketed diet in a 45-year-old woman with no previous thyroid disease. Signs of hyperthyroidism occurred shortly after a kelp-containing diet. Hyperthyroidism lasted 2 months and was followed by an over hypothyroidism…

“After 3 months of levothyroxine substitutive therapy, normal thyroid function was recovered after levothyroxine discontinuation. This clinical history is compatible with a case of iodine-induced thyrotoxicosis followed by prolonged block of the sodium-iodide symporter activity as a consequence of excessive iodine consumption from kelp. Consumers of marketed diets containing kelp of other iodine-rich ingredients should be advised of the risk to develop a thyroid dysfunction also in the absence of underlying thyroid disease.”

Contrast CT Scans Can Also Pose a Hyperthyroid Risk

Many physicians are quick to warn about dietary supplements. The authors of the first article from the Journal of General Internal Medicine concluded:

“Dietary supplements and herbal remedies are used by an increasing number of patients without prior medical consultation. Therefore, patients with known thyroid disease should be advised to avoid all complementary and alternative medications that contain iodine. Before starting any such supplements, patients with underlying thyroid disorder should check with their physician or pharmacist.”

What many physicians (and some radiologists) may not realize is that when they order a CT scan with contrast or cardiac catheterization, they could also trigger hyperthyroidism. That’s because the contrast material often contains iodide-containing material. Here is just such a case that was reported on our website along with scientific documentation of the link to hyperthyroidism.

The People’s Pharmacy Bottom Line:

We’re glad you worked with your doctor and got good results, but we don’t generally recommend this approach. For one thing it is hard to control the iodine dose with dietary supplements. Some kelp products may contain more iodine than is safe. Too much iodine can trigger hyperthyroidism and that can be a very dangerous situation.

You can learn more about hyperthyroidism, hypothyroidism, thyroid functioning, diagnostic testing and thyroid treatment in our Guide to Thyroid Hormones. In this 25-page downloadable PDF publication you will learn why some people do not do well on levothyroxine (Synthroid) prescriptions and why some people need both T3 and T4 supplementation. You will also learn why taking your thyroid supplement at night before bed might be more effective than taking it around breakfast time.

The original article on kelp was published August 9, 2009 but we felt that it was important to update you on the latest scientific findings with regard to kelp, iodine and contrast material. Please vote on this article and share your own story or comment below.

Join Over 80,000 Subscribers at The People's Pharmacy

Each week we send two free email newsletters with breaking health news, prescription drug information, home remedies and a preview of our award-winning radio show. Join our mailing list and get the information you need to make confident choices about your health.

  1. Dianne

    I recently discovered dried, roasted seaweed snacks, which are high fiber, low calorie (50/5g. pkg) and (relatively) low salt (50mg). I use them as a substitute for potato chips, and to alleviate acid reflux. I do have a multinodular goiter, but my TSH is within normal range (2.6). I am 72. I cannot find out what the iodine content is. Could these be harmful? I eat about 5 g. a day.

  2. Mary

    Since testing for iodine levels is rare, how can I be sure I do have enough in my body?

    The other halogens: bromine, chlorine and fluoride do restrict how much iodine can be utilized by the body.

  3. Mary

    I keep hearing that most of us are not deficient in iodine. With the increase of mercury in seafood, we probably get less iodine than we did in the past.

    Iodize salt is a placebo. Look at how much salt you would need to consume to get much benefit. I purposely went to gourmet salts w/o added iodine.

    Since most of us are exposed to the halogens fluoride, bromine, and chlorine, and all make it impossible for the thyroid to receive iodine, AND we are not being tested for our levels, HOW can they know that most of us get sufficient iodine?

    Iodine is needed throughout the body, not just the thyroid. Breasts are high on the list.

    • The People's Pharmacy

      Iodized salt is an effective public health measure, but we are being admonished to cut back on salt. The high levels of salt in our food come mainly from processed foods, and that salt is not necessarily iodized.

  4. Lyn

    Thank you for this article. It was very informative. Kelp is one of those very touchy supplements. Now I know I will stay away from it.

  5. Penny

    I was taking Kelp for one year and found that my tsh level went from 5 to 9. Should this happen?

What Do You Think?

We invite you to share your thoughts with others, but remember that our comment section is a public forum. Please do not use your full first and last name if you want to keep details of your medical history anonymous. A first name and last initial or a pseudonym is acceptable. Advice from other commenters on this website is not a substitute for medical attention. Do not stop any medicine without checking with the prescriber. Stopping medication suddenly could result in serious harm. We expect comments to be civil in tone and language. By commenting, you agree to abide by our commenting policy and website terms & conditions. Comments that do not follow these policies will not be posted.