Lesson 2. Iodine Controversy

Nutritional guide for Hashimoto’s disease series

Iodine is an essential mineral for normal thyroid function, breast tissue development and fetal and infant growth. The thyroid gland extracts iodine from various foods and requires an adequate amount of iodine for the thyroid hormone production.

In an adult with sufficient iodine intake, approximately 15 to 20 mg of iodine is concentrated in the tissues of the thyroid gland which accounts for about 30% of the body’s iodine supply. The remaining non-hormonal iodine is found in a variety of tissues such as eye, gastric mucosa, cervix, mammary and salivary glands.

The United States RDI recommended daily intake for dietary iodine is 150 mcg for adults, 220 mcg for pregnancy, and 270 mcg during lactation. The safe upper limit has been set at 1000 mcg (1 mg) as a result of studies assessing TSH levels with supplementation.

Iodine Deficiency

When there is not enough iodine in the diet, the pituitary gland makes more TSH continuing to stimulate the thyroid gland, causing it to enlarge and forming a goiter. The person becomes hypothyroid or subclinical hypothyroid.

Lack of iodine adversely affects brain development. Maternal iodine deficiency is the most preventable cause of mental retardation in infants and children. The severity and potential irreversibility of the brain damage are related to the degree of iodine deficiency and period of life during which the child was exposed to it.

Iodine deficiency is also associated with increased risk for thyroid carcinoma in humans.

Iodine deficiency is primarily found in Africa, Southeast and Central Asia. However, countries in Europe including Germany, France, Italy and Belgium are also prone to iodine deficiencies.

Although North Americans are considered an iodine sufficient population, that assumption is changing. Recent evidence shows that iodine deficiency and higher incidence of goiter is also common among adult women in the United States living mainly along the northern border of the country and in the upper mid-western states.

It is also important to check for other nutritional deficiencies that have relationships with iodine. Selenium is probably the next most important mineral affecting thyroid function and always have to be taken into a consideration. Supplementing with iodine will exacerbate the selenium deficiency. The opposite is also true: supplementing with selenium in a presence of an iodine deficiency will magnify and make the iodine deficiency worse.

Iodine Excess

With introduction of iodized salt, iodine deficiency has dramatically reduced in most of the industrialized countries. However, at the same time autoimmune thyroiditis became the most common cause of hypothyroidism.

Excessive  iodine can permanently damage the thyroid gland causing a goiter and trigger autoimmune thyroid disease Hashimoto’s thyroiditis in genetically susceptible individuals or make an existing condition worse.

The excess of iodine in the diet can stimulate the immune system to create antibodies that can attack the thyroid gland. As a result, the thyroid starts to produce less hormones and with time hypothyroidism may occur.

Nearly all patients with chronic autoimmune thyroiditis have high concentrations of TPO antibodies and/or Tg antibodies. In the individuals with elevated thyroid antibody levels, progression of hypothyroidism is correlated with increasing iodine intake.

Thyroid antibodies can be common in apparently healthy people with sufficient and excessive iodine intake as well as in populations with mild and moderate iodine deficiency. However, the mechanisms behind the development of thyroid antibodies in iodine sufficient and iodine deficient individuals may be different.

When thyroid antibodies may be secondary to goiter formation in iodine deficiency, a sudden excessive increase in iodine intake may enhance thyroid autoimmunity and make the Hashimoto’s disease to progress.

Supplementation over the amount of 20 mg of iodine or iodide has been shown to potentially contribute to underlying thyroid pathology in those with Hashimoto’s thyroiditis, Graves’ disease, or the progressive growth of nodularities in euthyroid individuals.

Iodine In Your Diet

Iodine levels in the human body depend on the diet. The foods rich in iodine are sea foods, iodized salt, fish from the oceans, kelp and seaweed.

Salt water fish, shellfish and seaweed are the dietary sources with the highest natural iodine content. For example, one bowl of soup made by tangle, which is common soup in the Japanese diet made from seaweed, can contain 5 mg iodide. Iodine content in fish and shellfish varies from less than 5 to more than 200 mcg per 100 g of cooked fish.

Ingestable iodine is commonly found in food coloring and seasonings and food processing agents. The bulk of dietary iodine however, is derived from milk and other dairy products and from bread prepared with iodate as a dough conditioner.

In many countries milk has high iodine content due to it being given to dairy cattle in mineral supplements. Mean iodine content in milk in Northern Europe is at the level of 15 to 20 mcg per 100 g of milk. The concentration of iodine is higher in the condensed milk.

List of iodine rich foods:


Iodized salt




Fish oils



Sea fish

Dough conditioner



Condensed milk

Sea food

Food coloring



Sea salt



Drinking water may contribute significantly to iodine intake in some countries. Furthermore, iodine intake depends on the market share of iodized products and their level of fortification. This makes it difficult to make any general conclusion about food choice and iodine intake.

Iodine is also found in some medication such as amiodarone and iodine based contrast dye. Many nutritional supplements, processed foods, cough medicines, diet pills and other medication contain iodine.

Do You Need To Supplement With Iodine?

Iodine is generally not recommended as a treatment for diagnosed thyroid conditions unless a genuine iodine deficiency is found. Iodine is of value for the thyroid hormone production if the thyroid gland is not functioning any more or removed. It is also not recommended for those with autoimmune thyroiditis as it can aggravate this condition especially if iodine is taken as a supplement.

Iodine increases the activity of thyroid peroxidase (TPO) which is an enzyme targeted by the immune system in Hashimoto’s disease patients. Most people will not show any symptoms, however, the elevated levels of the TPO antibodies will indicate an autoimmune flare-up. You can learn more about how excess of iodine can make Hashimoto’s and hypothyroidism worse here

Recent research studies reported that hypothyroidism caused by Hashimoto’s disease is reversible in some cases. The iodine restriction in the diet could be a predictable factor for restoring the thyroid function in Hashimoto’s patients with hypothyroidism.

According to different studies, between 50 and 80% of patients with hypothyroidism caused by Hashimoto’s disease were able to regain their thyroid function spontaneously after dietary iodine restriction only without using a thyroid hormone replacement.

In the patients with moderate hypothyroidism recovery was noticed as early as 3 months after the following low iodine diet. Patients with severe hypothyroidism have shown significant improvement and could possibly regain their normal thyroid function after long term iodine restriction.

During the experiment iodine rich foods were substituted with foods containing less iodine such as breads backed with iodine-free salt, mineral water instead of tap water, unsalted butter, home-made soups and sauces and restricted amounts of cheese, milk, fruits, fruit juices, pork, beef and veal. Some spices are hidden sources of high iodine. For example, colouring agent E-124 cochenille red A should be used instead of E-124 erythrosine.

Although iodine is only one of many environmental factors that could trigger Hashimoto’s disease, it could be evaluated through testing and be avoided by following a low iodine diet in order to reduce thyroid inflammation in people with Hashimoto’s disease.

But what about those Hashimoto’s patients who have low iodine levels? It is a well-known fact that low iodine levels can also trigger Hashimoto’s thyroiditis. In the article How Low Iodine Levels Can Cause Hashimoto’s Disease Dr. Alexander Haskell, ND talks about his treatment approach in reducing thyroid inflammation and restoring healthy iodine levels in Hashimoto’s patients who have iodine deficiency.


If you got here from Twitter or a link from a friend, why not pick up the whole series? This is one of the lessons in a free e-mail course Nutritional guide for Hashimoto’s disease. You can find out more about it and sign up here.


Comprehensive handbook of iodine: nutritional, biochemical, pathological and therapeutic aspects by V.R. Preedy, G.N. Burrow, R. Watson, Academic Press, 2009

Thyroid gland development and function by G. van Vliet, M. Polak, Karger Publishers, 2007

Thyroid disorders during pregnancy, Dtsch Med Wochenschr. 2009 Jan;134(3):83-6. Epub 2009 Jan 13.

Environmental factors altering thyroid function and their assessment. Environ Health Perspect. 1981 Apr;38:71-82.

Iodine: deficiency and therapeutic considerations, Alternative Medicine Review, vol. 13, Nr. 2 2008

The effect of iodine restriction on thyroid function in patients with hypothyroidism due to Hashimoto’s thyroiditis. Yonsei Med J. 2003 Apr 30;44(2):227-35.