iodine

Foods Richest in iodine

About iodine

Basic description

Surprisingly little research exists on the role of iodine in human health relative to the extensive study of iodine in environmental science. Some environmental context is useful here, as it may inform future research about iodine and health.

Iodine functions in ocean, soil, and atmospheric chemistry. The stability of the earth’s ozone layer, for example, is known to have a relationship to iodine levels in the atmosphere. Atmospheric iodine, in turn, is known to be related to iodine balance in the oceans and in the soil. Scientists also know that iodine concentrations in the atmosphere influence a wide range of oxygen-based reactions. Iodine has also been studied within the context of soil and plant health. Based on research in this area, we know that in some plants—for example, lettuce—iodine can help to offset stresses that get placed on the plants to due excess presence of salt in the soil (salinity stress).

These environmental roles of iodine in oxygen-based reactions and mineral balance (particularly involving sodium, potassium, and chlorine) have not been studied as extensively in human physiology, and future research is needed. However, the role of iodine in thyroid gland function has been studied in depth and is covered later in this profile.

Approximately 30% of WHF contain some iodine, with most food groups represented. In the vegetables group, for example, you will find sweet potatoes, onions, and spinach. In the fruit group, you will find strawberries, banana, and cantaloupe. In the grains you will find barley, and in the nuts you will find peanuts. (Although we list peanuts under “Nuts & Seeds” on our website, they are technically classified as legumes). Yet despite the presence of iodine in this diverse group of foods, it is difficult to get the recommended daily amount of 150 micrograms without consuming foods from two food groups not listed above. These two groups are Seafood and Eggs & Dairy. In fact, only 11 WHF rank as good, very good, or excellent sources of iodine, and these two groups (Seafood and Eggs & Dairy) account for over 90% (10/11) of all of all iodine-ranked foods. The Summary of Food Sources section covers this relationship in more detail.

At one point in time, iodine deficiency was fairly common in most of the northern part of the United States. This “goiter belt” included New England, the upper Great Lakes region, and the Pacific Northwest. The combination of iodine-depleted soils and lack of access to (or lack of acceptance of) seafoods left up to 30% of the population with severe iodine deficiency and its telltale goiter. (“Goiter”—a word that comes from the Latin “guttur” meaning “throat”—is a non-technical term that refers to enlargement of the thyroid grand. While iodine deficiency is one of the reasons that the thyroid gland can become enlarged, it does not always become enlarged following iodine deficiency and it can become enlarged for other reasons not involving dietary iodine.)

Starting in the early 20th century, an Ohio doctor aptly named David Marine began experimenting with adding iodine to local diets by way of iodized salt. (An apt name, given that seafoods are such an important dietary source of iodine.) By the 1920s, widespread consumption of this fortified salt in the U.S. had largely eliminated widespread iodine deficiency. The issue of iodized table salt is discussed—and its potential role in your meal plan—later in this article.

Role in health support

As described earlier, even though researchers know a good bit about iodine in relationship to the environment, less is known about other health support roles for iodine in the body. However, one area in which we are not lacking for information is the role of iodine in thyroid health.

Thyroid hormone production

Iodine is a key component of the hormones made in the thyroid gland. These hormones are absolutely critical to human health, helping to control energy production and utilization in nearly every cell of the body.

The balance of iodine in the thyroid gland is tricky, and both too much and too little iodine can slow down the production of hormones. This is not a situation where more is always better. The WHF recommended daily intake level of 150 micrograms aligns with general public health recommendations for preserving balanced production of thyroid hormones. For most people, falling far below this level or greatly exceeding it would potentially increase the risk of imbalanced thyroid hormone production.

Summary of food sources

When it comes to iodine, one food stands so far above the rest that the chart at the top of the page almost looks like a misprint. Some sea vegetables contain as much as 500% of the Daily Value (DV) per serving.

This is only true, however, for some sea vegetables. A good rule of thumb is that the brown sea vegetable species—for instance, kelp and wakame—are richer in iodine than the red forms. Still, we view sea vegetables (regardless of variety) as a potentially concentrated source of iodine, and anyone consuming 1 tablespoon or more of these foods on a daily basis mighty want to evaluate their total daily intake of iodine to make sure it does not exceed the Tolerable Upper Limit (UL) established by the National Academy of Sciences for adults 19 and older of 1,100 micrograms. For more on iodine and how to pick sea vegetables, read our profile on these interesting and useful foods.

Sea vegetables like kelp and wakame are not the only sea-based foods rich in iodine, however. All six of the WHF seafoods rank as good, very good, or excellent sources of this mineral. In the excellent category you will find scallops and cod. In the very good category you will find shrimp. And in the good category you will find tuna, salmon, and sardines. Both cod and scallops will provide you with nearly 90% of the daily recommended amount for iodine in a single 4-ounce serving. Note that many fish not profiled on our website contain significant amounts of iodine, generally falling into the range of 25-140 micrograms per 4-ounce serving. As a general rule (that does have numerous exceptions, however), shellfish are more concentrated in iodine than finfish.

Two of two dairy foods—cow’s milk and yogurt—as well as eggs rank as very good sources of iodine. You can get about 20% of your daily iodine from 4 ounces of cow’s milk, 1 egg, or 1/2 cup of yogurt.

The WHF that we have described above account for all but one of the ranked food sources of iodine. The only source we haven’t mentioned are strawberries, which rank as a very good source and provide about 13 micrograms per cup. (This ranking is largely due to the fact that strawberries are a high-water and low-calorie fruit, providing only 46 calories per cup.) While you would not want to rely on strawberries for your iodine intake, it would not be unreasonably to expect strawberries to provide about 10% of the iodine you need on any given day when you choose to eat them.

As described earlier, you can find foods in the vegetable group (like sweet potatoes, onions, and spinach), other foods in the fruit group (like bananas and cantaloupe), and foods in the grain group (barley) as well as the nuts group (peanuts, which are technically classified as legumes rather than nuts) that provide iodine. Like strawberries, however, you would not want to rely heavily on these foods to provide you with your daily iodine requirement. Conservatively speaking, including these non-seafood, non-dairy foods in your day’s food would most likely provide you with about 5-30% of the iodine you need.

As you can see from the above food summary, people who enjoy eating seafood on a near-daily basis have a good chance of meeting their daily iodine needs because they will often be able to get 50% of more of those needs from the seafood alone. A single serving of dairy foods on the same day might move this percentage up closer to 75%, and other foods would be able to make up the remainder.

For people who completely avoid seafood in their meal plan, iodine needs become a little bit trickier to meet. One meal plan addition worthy of consideration here would be to choose sea vegetables as a recipe component. Since 1 tablespoon of a sea vegetable like dulse can provide five times the daily iodine requirement all by itself, you could enjoy a recipe with this amount of sea vegetable and meet your iodine requirement over a five-day time period. Our 5-Minute Miso Soup with Dulse recipe will provide you with exactly that amount per serving. Dried kelp flakes or other forms of dried sea vegetables can be sprinkled on top of many dishes, and it is important to remember that it only takes one-fifth of a tablespoon—just a little bit more than half a teaspoon—to meet your recommended daily iodine level.

Of course, another alternative available to everyone is iodized salt. Iodized salt is a fortified form of table salt that has been processed to contain significant amounts of iodine. The general government standard for fortification of salt with iodine is 76-77 micrograms of iodine per gram of salt. However, many iodized salts don’t actually end up containing this much iodine. An average marketplace range seems to be closer to 45-50 micrograms per gram. Still, at 6 grams per teaspoon, this level of 45-50 micrograms would mean that 1 teaspoon of iodized salt would be likely to contain at least 270-300 micrograms of iodine and 1/4 teaspoon would be likely to contain at least 67-75 micrograms. So it is easy to see how 1/4 teaspoon of iodized salt could provide about half of a person’s daily recommended iodine. (This same 1/4 teaspoon would provide about 580 milligrams of sodium, or about 12% of the Daily Value.)

As a general rule, we always prefer whole, natural foods as a source of all nutrients, and there simply isn’t any form of iodized salt that is whole and natural. By definition, iodized salt is a processed, fortified ingredient. It is possible, of course, to purchase iodized sea salt, but even in this situation, the sea salt has been fortified with iodine during processing. (While iodine is naturally present in sea salts along with other minerals, it is not present in amounts that would qualify the salt to be labeled as “iodized.”)

In addition to our preference for whole, natural foods as a source of all nutrients, we also emphasize the pleasures of herbs, spices, and natural flavors found in fresh foods. The idea of substituting salt for the true pleasures of good cooking does not make sense to us. (That’s why you will find many of our recipes to be devoid of table salt as an ingredient, and our ingredients followed by the option, “salt and pepper to taste.”)

At the same time, we are not aware of any special problems related to the process of fortifying salt with iodine. In addition, we realize that many people rely on small amounts of iodized salt to boost up an otherwise deficient iodine intake level. Especially for persons who avoid seafood and dairy in their meal plans, iodized salt might make a logical addition to meet daily iodine needs. Obviously, the decision about whether to include iodized salt in a meal plan is a personal decision. From our perspective, it could be a very sensible choice, depending on all of the circumstances involved. We would, however, caution anyone who has been placed on a salt-restricted diet, or who suspects that they might fall into the minority of U.S. adults who are salt-sensitive in terms of blood pressure regulation, to talk over their best options for meeting daily iodine needs with their healthcare provider.

We would like to add one final note here on the relationship between salt and iodine intake. Processed foods in the U.S. have a well-deserved reputation for being overly high in salt. This trend has not been limited to fast foods or foods at a corner grocery. Many popular canned soups, frozen vegetables, and other widely enjoyed pre-packaged foods contain large amounts of salt. However, the salt added to processed foods is typically not iodized salt that has been fortified with iodine. For this reason, it simply is not correct to assume that consumption of a processed, high-sodium food is likely to provide you with the iodine you need, even if you venture out into processed, prepackaged foods as a regular part of your diet.

Nutrient rating chart

Introduction to nutrient rating system chart

Read more background information and details of our rating system

WHF ranked as quality sources of
iodine

Food

Serving
Size

Cals

Amount
(mcg)

DRI/DV
(%)

Nutrient
Density

World’s
Healthiest
Foods Rating

Sea Vegetables

1 TBS

10.8

750.00

500

829.5

excellent

Scallops

4 oz

125.9

135.00

90

12.9

excellent

Cod

4 oz

96.4

132.00

88

16.4

excellent

Yogurt

1 cup

149.4

71.05

47

5.7

very good

Shrimp

4 oz

134.9

46.00

31

4.1

very good

Cow’s milk

4 oz

74.4

28.06

19

4.5

very good

Eggs

1 each

77.5

27.00

18

4.2

very good

Strawberries

1 cup

46.1

12.96

9

3.4

very good

Sardines

3.20 oz

188.7

36.00

24

2.3

good

Salmon

4 oz

157.6

32.00

21

2.4

good

Tuna

4 oz

147.4

23.00

15

1.9

good

World’s Healthiest
Foods Rating

Rule

excellent

DRI/DV>=75% OR
Density>=7.6 AND DRI/DV>=10%

very good

DRI/DV>=50% OR
Density>=3.4 AND DRI/DV>=5%

good

DRI/DV>=25% OR
Density>=1.5 AND DRI/DV>=2.5%

Impact of cooking, storage and processing

Iodine is stable to storage and many types of processing. For example, we don’t see loss of iodine in sea vegetables, even if stored for long periods of time. You do not need to choose or store your iodine-rich foods in a special way to protect against loss. We do recommend, however, that you take a quick glance at the sea vegetables profile to help you select the best types for your nutritional and culinary needs.

As you cook iodine-rich foods, you will extract a significant portion of the iodine into the cooking water. This can be a good thing for nutrition, for example when you are making soup stock. Boiling sea vegetables for 15 minutes can extract from half to almost all its iodine content into the stock, making this soup now a great source of iodine nutrition.

Although becoming less popular, the use of iodine-containing dough conditioners to help to strengthen integrity of bread still remains a common practice. The iodine used in this processwill be listed on the food label as calcium iodate.

Risk of dietary deficiency

The risk of iodine deficiency is substantial in the United States and has been on the rise. The average urinary iodine level—a good measure of recent dietary iodine intake—has dropped by more than half since the 1970s. Of course, we are talking about a very broad population-level trend here, in a country where processed, prepackaged foods play a major role in the average U.S. adult meal plan.

The reason we see iodine levels dropping in the population is two-fold. One is that within the world of commercial baking, many bread manufacturers have moved away from iodine-containing compounds to keep dough fresh. But a bigger change is that the average U.S. household is doing less and less home cooking and resorting more and more often to prepackaged foods, ready-to-eat foods, and restaurant eating (including fast food eating). As mentioned earlier, even though many prepackaged foods are high in sodium, the salt added to these foods has not necessarily been fortified with iodine.

Still, there is a good bit of unpredictability in the iodine content of prepackaged and ready-to-eat foods. Some food preparers use salt that is iodized, including some fast food restaurants. But because the level of iodine in “away-from-home” foods can be so unpredictable, we recommend that you focus on obtaining iodine from whole, natural foods. The food sources of iodine section above should help you figure out what combination of whole, natural foods will work best for you.

Perhaps most concerning is the recent finding that the average pregnant woman in the United States has substandard iodine nutrition. Iodine—as a constituent of thyroid hormone—is critical to the developing nervous system, and low iodine levels in children are associated with impaired development.

Counter-balancing this concern is evidence from the most recent National Health and Nutrition Examination Survey which shows that this drop in iodine intake has stabilized. So while we need to do a better job of making sure at-risk people—especially pregnant women—get enough iodine, at least the public health problem is not continuing to get worse.

Other circumstances that might contribute to deficiency

Iodine content of soils varies by region. At one point in time, when food didn’t travel very far to get to the plate, the low-iodine region of the Great Lakes region was referred to as the “goiter belt” due to problematic iodine nutrition. Because food travels much more in our modern supply chain, regional differences in soil iodine content don’t play as prominent a role as in earlier periods of U.S. history.

Because fish and dairy foods are among our richest sources of iodine, vegans (individuals who eat no animal foods products whatsoever) appear to be at increased risk of iodine deficiency. A 2011 study found that the average U.S. vegan had a urinary iodine level that would be considered deficient. Even among this at-risk group, however, we did not see thyroid disease related to the low-iodine diets. Note that vegetarians who include milk and eggs in their diets end up with iodine levels very similar to the entire population.

There are compounds called thiocyanates in some commonly consumed foods. At high concentrations, these chemicals can interfere with the uptake of iodine into the thyroid gland, making a person seem like they have iodine deficiency, when they may not. The common thiocyanate containing foods include cassava, soy, and Brassica family vegetables. Tobacco smoke also contains thiocyanates.

The most commonly reported version of thiocyanate-related disease is seen in areas of Africa where cassava root is an important dietary staple. In the U.S., we occasionally see this issue related to soy-based infant formulas, but even then almost exclusively in infants born with thyroid disease

At the amounts typically consumed, at the amounts we consume these foods regularly, there is not compelling evidence of significant risk. For example, a 2011 study found no association between reported intake or soy or blood concentrations of soy nutrients and problems with thyroid function in pregnant women, a group otherwise at high risk for thyroid disease. For more on this topic, click through to this article about thiocyanate containing foods and thyroid disease.

The most likely thyroid disruptors in the environment are not in foods, but in medications or man-made toxins. Lithium (used to treat bipolar disorder) and phenylbutazone (used as an anti-inflammatory) are examples of drugs that can impair iodine nutrition.

Perchlorate, a chemical used in rocket fuel, is an environmental toxin found in water supplies in the U.S. at varying concentrations. It can also impair uptake of iodine into the thyroid. According to the Natural Resources Defense Council, if you have perchlorate in your water, you’ll need a reverse osmosis filter to effectively remove it.

Relationship with other nutrients

Selenium

We also know that deficiency of iron makes the thyroid dysfunction seen in iodine deficiency worse. At this point in time, we don’t have a clear explanation why. We do know, however, that this is a big public health problem worldwide, especially in the developing world.

Risk of dietary toxicity

There is an acute toxicity that can occur from excessive iodine intake that leads to mouth pain, nausea, and vomiting. This almost never occurs from dietary iodine alone, and if it did, it would require that another serious medical condition (e.g., kidney failure) be present.

The Tolerable Upper Intake Limit (UL) of 1,100 mcg / day is set by the National Academy of Sciences in its Dietary Reference Intakes (DRIs) to prevent more chronic and subtle health problems related to iodine overconsumption. Oddly, diets high in iodine are associated with increased size and decreased function of the thyroid gland, the very same symptoms we see with too little iodine. The UL of 1,100 micrograms applies to adults ages 19 and older. For teens 14-18 years of age, the UL is set lower at 900 micrograms, and for teens 9-13 years, at 600 micrograms. For children 4-8 years of age, the iodine UL is 300 micrograms, and for children 1-3 years, it is 200 micrograms. You can review the full range of DRIs for iodine in our Public Health Recommendations section.

Luckily, diets that routinely go above the UL for iodine appear to be rare in the US, as well as throughout the world. The easiest way to get to iodine excess would be heavy consumption of sea vegetables, which can contain up to four times the UL in a single one-quarter ounce serving. For best thyroid health, the most iodine-dense varieties are best treated as the most iodine-rich sea vegetables a “sometimes” food rather than a daily indulgence.

Heavy use of iodized salt could also be a contributor toward excess iodine consumption. Iodine can be added to salt at amounts up to 77 mcg per gram. If a person was consuming 5,000 mg of sodium from iodized salt—a fairly standard sodium intake for 25% of adult U.S. males—that person might be getting just shy of 1,000 mcg of iodine per day. Of course, this example makes the unlikely assumption that all the salt in a person’s diet had been fortified with iodine. As described earlier, this situation would be unlikely, since most processed, high-sodium foods have not been processed using iodized salt.

Disease checklist

• Goiter
• Hypothyroidism
• Skin infection
• Fibrocystic breast disease

Public health recommendations

In 2001, the National Academy of Sciences established a set of Dietary Reference Intakes (DRIs) for iodine. This set of recommendations included Recommended Dietary Allowances (RDAs) for all individuals over 1 year of age, and Adequate Intakes (AIs) for infants under 1 year. These DRI recommendations are as follows.

• 0-6 months: 110 mcg
• 6-12 months: 130 mcg
• 1-8 years: 90 mcg
• 9-13 years: 120 mcg
• 14+ years: 150 mcg
• Pregnant women: 220 mcg
• Lactating women: 290 mcg

The DRI report also established a Tolerable Upper Intake Levels (ULs) for iodine. These ULs vary with age. For adults 19 years and older, the UL is set at 1,100 micrograms per day. For teens 14-18 years of age, the UL is set lower at 900 micrograms, and for teens 9-13 years, at 600 micrograms. For children 4-8 years of age, the iodine UL is 300 micrograms, and for children 1-3 years, it is 200 micrograms. The iodine ULs are intended as average maximum limits. Occasionally going above the UL is not generally believed to be health concern.

The Daily Value (DV) for iodine is 150 mcg. This is the value that you will see on food and supplement labels, and the value that we have chosen as WHF daily recommended amount.

Description

What is iodine?

If you backpack in the mountains, you may have used iodine tablets to purify your drinking water. Or, perhaps you’ve used an iodine-based disinfectant to clean a minor skin wound. But did you know that iodine is essential to life?

Iodine, a trace mineral, is required by the body for the synthesis of the thyroid hormones, thyroxine (T4) and triiodothyronine (T3). (T4 contains 4 iodine atoms. When one of the iodine atoms is stripped off of T4, it becomes T3, with 3 iodine atoms remaining.)

Under normal circumstances, ythe body contains approximately 20 to 30 mg of iodine, most of which is stored in your thyroid gland, located in the front of your neck, just under your voice box. Smaller amounts of iodine are also found in lactating mammary glands, the stomach lining, salivary glands, and in the blood.

How it functions

What is the function of iodine?

As a component of the thyroid hormones thyroxine (T4) and triiodothyronine (T3), iodine is essential to human life. Without sufficient iodine, ythe body is unable to synthesize these hormones, and because the thyroid hormones regulate metabolism in every cell of the body and play a role in virtually all physiological functions, an iodine deficiency can have a devastating impact on your health and well-being.

Regulating thyroid hormones

The synthesis of thyroid hormones is tightly controlled. When the amount of thyroid hormone in your blood drops, the pituitary gland secretes a hormone called thyroid-stimulating hormone (TSH). As its name suggests, TSH then stimulates the thyroid gland to increase its uptake of iodine from the blood, so that more thyroxine (T4) can be synthesized. When necessary, thyroxine is then converted to the metabolically active triiodothyronine (T3), a process that involves removing one iodine atom from T4.

Several other physiological functions for iodine have been suggested. Iodine may help inactivate bacteria, hence its use as a skin disinfectant and in water purification. Iodine may also play a role in the prevention of fibrocystic breast disease, a condition characterized by painful swelling in the breasts, by modulating the effect of the hormone estrogen on breast tissue. Finally, researchers hypothesize that iodine deficiency impairs the function of the immune system and that adequate iodine is necessary to prevent miscarriages.

Deficiency symptoms

What are deficiency symptoms for iodine?

In the early part of the 20th century, iodine deficiency was quite common in the United States and Canada. However, this problem has since been almost completely resolved by the use of iodized salt. In addition, iodine is now added to animal feed, which has increased the iodine content of commonly consumed foods, including cow’s milk.

Unfortunately, in countries where iodized salt is not commonly consumed, iodine deficiency remains a signficant problem. Dietary deficiency of this vital mineral results in decreased synthesis of thyroid hormone.

Goiter, or enlargement of the thyroid gland, is usually the earliest visible symptom of iodine deficiency. (Goiter can occur for many other reasons as well, but iodine deficiency is among the most common causes worldwide.) The enlargement of the thyroid results from overstimulation of the thyroid gland by thyroid stimulating hormone (TSH), as the body attempts to produce increased amounts of thyroid hormone.

Goiter is more common in certain geographical areas of the world where iodine is lacking in the diet and where selenium is lacking in the soil. (Selenium is directly involved with certain activities of the thyroid gland.)

Iodine deficiency may eventually lead to hypothyroidism, which causes a variety of symptoms including fatigue, weight gain, weakness and/or depression. Interestingly, iodine deficiency can also cause hyperthyroidism, a condition characterized by weight loss, rapid heart beat, and appetite fluctations.

Severe iodine deficiency during pregnancy or infancy causes cretinism, a condition characterized by hypothyroidism leading to failure of the thyroid gland and/or severe mental retardation, stunted physical growth, deafness, and spasticity. If discovered in its initial stages, cretinism can be corrected with iodine supplementation.

Toxicity symptoms

What are toxicity symptoms for iodine?

Accidental overdose of iodine from medications or supplements in amounts exceeding one gram may cause burning in the mouth, throat and stomach and/or abdominal pain, nausea, vomiting, dirarrhea, weak pulse, and coma.

It is difficult to take in too much iodine from food sources alone. It is estimated that men and women consume at most 300 mcg and 210 mcg of iodine per day, respectively. In general, even high intakes of iodine from food are well-tolerated by most people.

However, in certain circumstances, excessive consumption of iodine can actually inhibit the synthesis of thyroid hormones, thereby leading to the development of goiter (enlargement of the thyroid gland) and hypothyroidism. Excessive iodine intake may also cause hyperthyroidism, thyroid papillary cancer, and/or iodermia (a serious skin reaction).

In an attempt to prevent these symptoms of iodine toxicity, the Institute of Medicine established the following Tolerable Upper Intake Levels (TUL) for iodine:

• 1-3 years: 900 mcg
• 4-8 years: 300 mcg
• 9-13 years: 600 mcg
• 14-18 years: 900 mcg
• 19 years and older: 1,100 mcg
• Pregnant women 14-18 years: 900 mcg
• Pregnant women 19 years and older: 1,100 mcg
• Lactating women 14-18 years: 900 mcg
• Lactating women 19 years and older: 1,100 mcg

It is important to note that if you have an autoimmune thyroid disease (for example, Grave’s disease or Hashimoto’s disease) or if you have experienced an iodine deficiency at some point in your life, you may be more susceptible to the dangers of excessive iodine consumption, and may, therefore, need to monitor your intake of iodine more carefully.

Factors that affect function

What factors might contribute to a deficiency of iodine?

Since absorption of iodine from the digestive tract is very thorough, deficiency of iodine typically occurs from too little intake of iodine-containing foods. However, there has been some controversy surrounding the impact of diet not on iodine absorption, but on iodine utilization by the thyroid gland. Since the thyroid requires iodine to make thyroid hormones, this utilization is essential. Two groups of substances found in food - isoflavones, most commonly found in soy foods, and thiocyanates, most commonly produced in the body from glucosinolates found in cruciferous vegetables like broccoli - have been shown to interfere with iodine utilization by the thyroid gland, but only under very specific circumstances. These circumstances involve simultaneous dietary deficiency of iodine or selenium (or both) and imbalanced overall dietary intake. We’re not aware of any evidence showing problems with iodine metabolism by the thyroid gland when either soy foods or cruciferous vegetables are eaten in moderate amounts in an overall balanced diet that also contains appropriate amounts of iodine and selenium. Since soy foods and cruciferous vegetables provide so many well-documented health benefits, we do not believe there is ordinarily any reason to eliminate these foods from the diet for iodine-related reasons. However, for individuals with a history of thyroid problems, poor dietary balance and deficient intake of iodine and/or selenium, we recommend consultation with a healthcare provider to decide about the role of these foods in health support.

Nutrient interactions

How do other nutrients interact with iodine?

The conversion of thyroxine (T4) to triiodthyronine (T3) requires the removal of an iodine molecule from T4. This reaction requires the mineral selenium. The iodine molecule that is removed gets returned to the body’s pool of iodine and can be reused to make additional thyroid hormones.

If ythe body is deficient in selenium, the conversion of T4 to T3 is slowed, and less iodine is available for the thryoid to use in making new hormones.

Animal studies have shown that arsenic interferes with the uptake of iodine by the thyroid, leading to goiter. In addition, dietary deficiency of vitamin A, vitamin E, zinc and/or iron can exaggerate the effects of iodine deficiency.

Health conditions

What health conditions require special emphasis on iodine?

Iodine may play a role in the prevention and/or treatment of the following health conditions:

• Cognitive impairment
• Cretinism
• Fibrocystic breast disease
• Goiter
• Hyperthyroidism
• Hypothyroidism
• Multiple miscarriages

Food sources

What foods provide iodine?

The amount of iodine found in most natural foods is typically quite small and varies depending on environmental factors such as the soil concentration of iodine and the use of fertilizers. Some of the richest food sources of iodine are often processed foods that contain iodized salt, and breads that contain iodate dough conditioners.

Sea vegetables are an excellent source of iodine. Yogurt, cow’s milk, eggs, and strawberries are very good sources of idone. Good sources include mozzarella cheese.

Fish and shellfish require their own special category when it comes to iodine content, because the amount of iodine they contain is not always easy to predict. For example, the amount of iodine found in fish may not match up very predictably with the amount found in their home waters, or even with their diet. Four ounces of very low iodine fish might only provide about 70 micrograms of iodine, or less than half of the adult RDA. By contrast, four ounces of very high iodine fish might contain as much as 1,000 micrograms of iodine—an amount just below the Tolerable Upper Limit (UL, or safety level) of 1,100 micrograms.

Due to the great variability in fish iodine content, and the relative lack of good information for consumers to base their nutritional decisions in this area, we would not recommend reliance on fish alone to provide all of your dietary iodine needs. However, you can count on getting iodine from most fish, and on any one particular day, we would recommend thinking about a 4-6 ounce fish meal serving as providing at least 50% of your iodine needs. Conversely, if you are trying to greatly restrict your iodine intake, you might want to eat fish on a less frequent basis to lower your risk of iodine intake above the RDA level.

Related Articles

• Are sea vegetables a good source of iodine?
• Feeling Great with Cruciferous Vegetables
• Radiation Protection and Diet
• Soy Foods and Thyroid Health
• What are goitrogens and in which foods are they found?
• What is meant by the term "goitrogen" and what is the connection between goitrogens, food, and health?
• Why are sea vegetables so important to a healthy diet?

References

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4. Cao Y, Blount BC, Valentin-Blasini L, et al. Goitrogenic anions, thyroid-stimulating hormone, and thyroid hormone in infants. Environ Health Perspect 2010;118:1332-7. https://doi.org/10.1289/ehp.0901736
5. Giray B, Arnaud J, Sayek, I, et al. Trace element status in multinodular goiter. J Trace Elem Biol 2010;24:106-10. https://doi.org/10.1016/j.jtemb.2009.11.003
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