In this article:
Iodine deficiency is the leading cause of hypothyroidism worldwide. Still, it is rare in the United States since iodized salt was introduced in the 1920s.
Iodine is a trace element found in some foods, added to others, and available as a dietary supplement. It does not occur naturally in the body.
Iodine supports healthy thyroid hormone production through ingestion. When TSH is secreted from the pituitary, it increases the thyroid's uptake of iodine. It stimulates the synthesis and release of thyroid hormones thyroxine (T4) and triiodothyronine (T3).
Thyroid hormones impact the function of every cell in the body. Without sufficient iodine, TSH levels remain elevated and lead to goiter, an enlargement of the thyroid gland that reflects the body's attempt to produce thyroid hormone.
Pregnant and nursing mothers also require iodine for proper development in fetuses and infants.
Hypothyroidism is a condition in which the thyroid gland is unable to make a sufficient amount of thyroid hormone to support normal body functions. The thyroid gland plays a role in supporting every cell in the human body. This butterfly-shaped endocrine gland secretes hormones that help cells utilize energy, regulate temperature, and support organ function.
There are various reasons that the thyroid gland can be underactive. In the United States, the most common cause of hypothyroidism is Hashimoto's thyroiditis. With this autoimmune condition, the immune system attacks cells in the thyroid gland. Thus, autoimmune disorders reduce the number of thyroid cells and enzymes that are available to produce thyroid hormone. People with Hashimoto's suffer from chronic inflammation of the thyroid, which leads to a gradual decline in thyroid function.
Other causes of hypothyroidism may include:
Surgical removal of the thyroid gland
Some people undergo partial or complete removal of the thyroid gland in response to thyroid nodules, thyroid cancer, or Graves' Disease.
Radioactive iodine (I-131) is a form of treatment for various thyroid conditions, including Graves' disease, thyroid cancer, or nodular thyroid. The purpose of radioactive iodine is to destroy the thyroid gland, which results in a person becoming hypothyroid. Furthermore, radiation aimed at treating lymphomas or cancers in the head and neck can damage the thyroid gland.
This condition is generalized inflammation of the thyroid gland that may be caused either by a viral infection or an autoimmune attack.
Certain medications can affect the way the thyroid produces hormones.
This mineral is essential for normal thyroid functioning. Finding a balance in iodine consumption is critical, as too much or too little iodine can worsen hypothyroidism.
Damage to the pituitary gland
The pituitary gland in your brain controls the thyroid gland. The pituitary gland dictates how much hormone the thyroid should produce to maintain healthy functioning in the body. Tumors, radiation therapy, and surgical alterations to this gland can interrupt communication between these two organs.
Iodine is a crucial component of the molecular structure of thyroid hormones.
The pituitary gland in the brain releases TSH (thyroid-stimulating hormone) when it detects that thyroid hormones T4 and T3 are low. TSH signals the thyroid gland to produce more T4 and T3. Cells in the thyroid gland produce T4 and T3 by combining iodine and tyrosine (an amino acid).
Once T4 and T3 are created, these hormones are distributed throughout the body to regulate metabolism. Iodine is absolutely necessary for the thyroid gland to produce T4 and T3.
The cells in the thyroid gland are the only cells in the body that absorb iodine. Without iodine, the thyroid gland cannot produce T4 and T3. Ultimately, the lack of thyroid hormones leads to hypothyroidism.
Iodine does not occur naturally in specific foods like other essential nutrients such as calcium, vitamins, and iron. Instead, iodine is found in soil and absorbed by the foods that grow in iodine-rich earth. Certain regions of the world are iodine-poor, including the Himalayas, the Alps, and Andes regions, and river valleys prone to flooding.
The most common cause of iodine deficiency is from an unhealthy diet. Iodine deficiency is more common in developing countries where access to healthy foods is limited. In developed countries like the United States, iodine deficiency is more likely in people who eat a diet that consists mostly of processed foods. While processed foods usually contain high levels of salt, the salt used in these foods is typically non-iodized. Iodine is not listed on the Nutrition Facts Panel unless the food has been fortified by iodine.
Environmental toxins can impact how iodine is consumed and processed by the thyroid. There are certain toxins that we may regularly ingest that can block iodine uptake. Examples of some of these toxins include bromide, chlorine, and fluoride. These toxins may be in water supplies, baked goods, or dental products.
Studies suggest that people who have other nutrient deficiencies such as iron, selenium, and Vitamin A may also be at higher risk for iodine deficiency.
Vegan or Paleo diet
Specific diets may contribute to the risk of iodine deficiency. Following a vegetarian, dairy-free, vegan, or paleo diet may lead to iodine deficiency because iodine-rich foods may be limited or avoided in these diets.
Cruciferous vegetables are high in goitrogens, which many believe to block the intake of iodine in the thyroid gland. However, those whose diets contain adequate iodine can safely consume these vegetables in reasonable amounts, especially when cooked.
Women who are pregnant or nursing may also become deficient in iodine. They should follow the Recommended Dietary Allowance recommendations for iodine intake.
Iodine deficiency manifests in three prominent symptoms, which each have numerous systemic effects in the body.
A goiter occurs when the thyroid gland enlarges. When a person has a goiter, it frequently means the person is deficient in iodine intake. This enlargement of the thyroid gland is a result of the thyroid working overtime to try to keep up with the body's demand for thyroid hormone.
When iodine levels fall, the thyroid gland has difficulty making thyroid hormone, which can lead to hypothyroidism. People with hypothyroidism experience an overall slowing of functions in the body which can cause:
- Weight gain
- Slow heart rate
- Elevated cholesterol
- Increased sensitivity to cold
- Puffy face
- Dry skin and thinning hair
- Irregular or heavy menstruation
- Muscle weakness and pain
- Joint pain and stiffness
Complications in pregnancy
Sufficient iodine intake is essential for women who are pregnant or nursing. If a pregnant woman is severely iodine deficient, the pregnancy may end in miscarriage, stillbirth, preterm delivery, and congenital abnormalities. Some babies born to women with iodine deficiency demonstrate intellectual and developmental disabilities. Even mild cases of iodine deficiency are associated with low mental capacity in children in developed countries where iodine deficiency is rare.
Conditions like hypothyroidism, goiter, or brain damage may develop in cases of severe iodine deficiency. Controversially, several studies show that excessive amounts of iodine are associated with increased rates of thyroid autoimmunity (Hashimoto's thyroiditis).
What's supposed to happen, in most cases of slight iodine deficiency, is that the thyroid compensates its use of iodine, keeping thyroid hormone production relatively normal.
However, high concentrations of iodine inhibit thyroid hormone production and release. This effect is known as the Wolff-Chaikoff effect and is influenced by the enzyme thyroid peroxidase. Thyroid peroxidase (TPO) converts iodide ions absorbed from food into an active form of iodine to be used by the body. This conversion creates hydrogen peroxide.
Too much iodine means an overabundance of hydrogen peroxide. Too much hydrogen peroxide can damage thyroid cells due to oxidative stress. An imbalance between pro-oxidant substances and antioxidant defenses causes this stress. Pro-oxidants are chemicals that induce cellular stress, and antioxidants protect your body's cells from damage. So, as iodine levels increase, cell death occurs more quickly.
Usually, a healthy immune system is responsible for protecting against foreign cells and caring for damaged cells. However, autoimmunity is a condition in which your immune system mistakenly attacks your body. It mistakes your cells as foreign and releases antibodies that attack healthy cells.
Thyroid autoimmunity (like Hashimoto's Thyroiditis) damages the thyroid gland, leading to chronic inflammation. Inflammation and oxidative stress are closely related processes. It seems that oxidative stress is a mechanism underlying the progress of inflammation.
Thyroid autoimmunity identifies TPO as a threat. Therefore, the immune system produces TPO antibodies to fight TPO and limit thyroid hormone production. When iodine levels remain high, the immune system fights even harder to keep thyroid hormone production low. This vicious cycle can lead to elevated TPO antibodies, and ultimately, Hashimoto's.
Hashimoto's disease is the most common cause of hypothyroidism in the United States, affecting roughly 5% of the population.
There are four different ways to measure iodine levels. Your doctor may order any of the following tests to assess for iodine deficiency:
Greater than 90 percent of dietary iodine leaves the body in the urine. A urine test is the simplest, quickest, and most common way to test for iodine deficiency. However, this test may not be as accurate as other testing options.
A blood test is an accurate way to test iodine levels.
Iodine patch test
In this test, a physician applies a patch of iodine to the skin and assesses if the skin has absorbed it after 24 hours. If a person is iodine deficient, the patch will be absorbed by the body before the 24-hour mark. While this test is not the most accurate, it is inexpensive and relatively quick.
Iodine loading test
Although this test requires 24 hours of urine collection, it is very accurate in measuring how much iodine leaves the body within 24 hours.
Iodine in food and iodized salt is present in several chemical forms, including sodium and potassium salts, inorganic iodine, iodate, and iodide, the reduced form of iodine. Iodine rarely occurs as the element, but rather as a salt.
Iodized salt was introduced in the United States in the 1920s to combat goiters. Many studies from the "goiter belt" of the United States (including the Great Lakes, Appalachians, and Northwest regions) find that people experience a significant reduction in goiter size by adding iodized salt to their diet.
Iodized salt is available across the U.S. today and is available in about 120 other countries worldwide. However, it is not mandatory for salt to be fortified with iodine in the United States. Furthermore, most Americans consume the majority of their salt in processed foods, which primarily use non-iodized salt in production.
Primary food sources of iodine include iodized salt, fish, seaweed, dairy, and grains. Iodine content can widely vary in food sources, especially in seaweed. Fruits and vegetables can also contain iodine, but these levels vary based on how the plants are processed. For example, soil content, fertilizers, and irrigation practices can alter the amount of iodine available in fruits and vegetables.
The table below lists food sources of iodine and their associated serving sizes and the percentage of daily value:
Many multivitamin or mineral supplements may contain potassium iodide or sodium iodide. Nutritional supplements of iodine or kelp are also available. People with Hashimoto's tolerate supplements containing up to 150 mcg of iodine without increasing thyroid antibodies. Iodine supplements have the potential to interact with other medications. If you take another regular medication, you should discuss your iodine intakes with your doctor.
The Recommended Dietary Allowance (RDA) for iodine is 150 micrograms (mcg) for adults, and 220 mcg and 290 mcg for pregnant and lactating women, respectively.
While the Tolerable Upper Intake Level (U.L.) for adults is 1,100 mcg per day, the U.L. is 400 mcg per day for people with Hashimoto's. The rationale? Research suggests too much iodine could be an environmental trigger for Hashimoto's disease, mainly when selenium status is low.
Studies show that iodine excess of 300 mcg per day can alter thyroid function and may spur the development of thyroid autoimmunity. So, if you are taking a supplement with iodine, it is important to track your daily iodine intake from both your vitamins and your food. In general, it is ideal for people with Hashimoto’s to consume between 100-300 mcg of iodine daily from different sources, however, it helps to work with a nutritionist to learn what amount is best for your thyroid function.
Recommendations for iodine intake in pregnancy
The current recommendation for daily iodine intake for pregnant women is 220 mcg. Because processed foods do not typically contain iodized salt, some pregnant and lactating mothers may have iodine deficiency.
The American Academy of Pediatrics and the American Thyroid Association recommend that pregnant and breastfeeding mothers take a supplement that contains at least 150 mcg of iodine and use iodized table salt.
If a mother is vegan or does not eat dairy or fish, she should have a urine test to assess for iodine deficiency. Furthermore, excess nitrates can potentially interfere with iodide transport, so familiar sources of excess nitrates, such as well water, should be checked regularly.
A note from Paloma Health
Iodine plays a crucial role in your thyroid health. Talk with your care team to determine if your iodine levels are appropriate, and how you might optimize your diet to support your thyroid function.