Iodine for hypothyroidism is a controversial topic, with experts on both ends of the spectrum arguing for and against its use. But if you have hypothyroidism, or know someone who does, it's important to understand that iodine is often not a preferred form of treatment, and in many cases can make your condition worse.
Before we delve into why that is, you're probably wondering about all of the good things you've heard about iodine, so allow us to explain …
Your Thyroid Needs Iodine to Function
Your body does not make iodine on its own, which means you must get it through your food. If you do not get enough, you will be unable to make sufficient amounts of thyroid hormone.
Your thyroid depends on iodine to produce two hormones, triiodothyronine (T3) and thyroxine (T4). The numbers in these hormone names are actually a marker of how many iodine atoms are attached, with T4 containing 4 atom molecules, then releasing one to convert into T3, the hormone's active form.
It's estimated that 2 billion people worldwide – including 266 million school-age children – have insufficient iodine intake,  and the resulting iodine deficiency is, in fact, the most common cause of hypothyroidism (underactive thyroid) worldwide.
If you have an iodine-deficient diet then eating iodine-rich foods like seaweed and even supplementing with iodine can quickly help to remedy the problem … but it's important to realize that in the United States iodine deficiency is not a major cause of hypothyroidism , and in many cases treating the condition with iodine is a major health disaster.
Iodine Deficiency is NOT a Major Cause of US Hypothyroidism Cases
Iodine levels in food vary greatly depending on soil and seawater concentration of iodine. Because of this it can be difficult to get sufficient iodine from diet alone, especially if you live in an area with iodine-deficient soil. To remedy this, the United States adds iodine to most table salt, which means you're not only getting extra iodine when you salt your food, but also when you eat processed foods, which are typically heavily salted with iodized salt.
Many animal feeds in the United States are also supplemented with iodine and as a result dairy products are also good food sources of this nutrient.
There have, however, been signs that iodine intakes in the United States have been dropping, possibly due to increased numbers of people cutting back on their salt intake, but data from the latest study available, the National Health and Nutrition Examination Survey 2003-2004 , suggests that most Americans are still getting enough. 
So, in the United States, iodine deficiency is not considered to be a major cause of hypothyroidism, except in specific at-risk groups, such as those who do not consume iodized salt (including that in processed foods), fish or seaweed, or women who are pregnant.
That said, cases of hypothyroidism are widespread in the United States, impacting nearly 4 percent of the population,  including 13 million who have not been diagnosed and are unaware they have the condition. 
If iodine deficiency is not the problem, then what is?
The Most Common Cause of Hypothyroidism in the United States
Hypothyroidism in the United States is most often the result of an autoimmune disease called Hashimoto's thyroiditis, or Hashimoto's disease, which causes your immune system to mistakenly attack, and destroy, the thyroid.
The disease typically begins with inflammation of your thyroid gland (thyroiditis) that over time impairs the ability of your thyroid to produce enough hormones, and eventually leads to underactive thyroid, or hypothyroidism.
The exact causes of Hashimoto's are unknown, but it's likely the result of a combination of factors including:
- A virus or bacteria that triggers the response
- Genetics / family history
- Gender (women are more likely to have Hashimoto's)
- Other environmental factors
However, and this is an important point, excess iodine may also worsen the condition.
Increasing Iodine May Worsen Hypothyroidism
There's no arguing that iodine is a crucial nutrient for your body … but in the case of hypothyroidism, more is not always better.
Studies show that giving iodine to people who had adequate or excessive iodine intake could actually trigger hypothyroidism and autoimmune thyroiditis.
Research also suggests that iodine actually increases the activity of the thyroid peroxidase (TPO) enzyme, and increased antibodies to this enzyme are common in Hashimoto's patients. It is the interaction between the TPO enzyme and the antibodies that leads to inflammation and destruction of the thyroid. In other words, too much iodine can actually make Hashimoto's worse.
Remember, since most hypothyroidism cases in the United States are due to Hashimoto's disease, NOT iodine deficiency, this study could apply to you …
Be Very Careful if Your Health Care Practitioner Automatically Recommends Iodine for Hypothyroidism
Many health care practitioners in the United States do not understand the complexities of thyroid function and will routinely recommend iodine supplements for people with hypothyroidism. This approach will, unfortunately, be detrimental for some.
If you are truly deficient in iodine, then supplementation or increased dietary intake is necessary. But if not, additional iodine will most likely only trigger or worsen your thyroid troubles.
So if your health care practitioner recommends iodine supplementation without any real evidence that you're deficient, it's a red flag to take note of. A second opinion from a practitioner who understands the complex role of iodine in hypothyroidism – and can discuss with you its benefits versus risks – is likely warranted.
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