Vegan Sources of Iodine – Are Supplements Necessary?

Iodine is an essential nutrient for thyroid function, yet it’s often overlooked in vegan diets. If we want to fuel our bodies appropriately and support the long-term sustainability of veganism, iodine is a nutrient we need to be aware of. 

Are there any good vegan sources of iodine? Do vegans need to take a supplement? Do fruits and vegetables contain iodine?

As a registered dietitian and vegan myself, I’ll answer these questions and more! Keep reading to learn why our bodies need iodine and how vegans can get enough of this important nutrient to best support their health. 

What is iodine?

Iodine is a trace mineral used by the thyroid gland to produce thyroid hormone.  Thyroid hormone is made up of two main hormones: thyroxine (T4) and triiodothyronine (T3). 

Thyroid hormone has many important roles in the body, including:

• Controlling your metabolic rate (metabolism)
• Protein synthesis
• Brain development in infants
• Regulating heart rate
• Digestion speed
• Muscle contraction
• Regulating the production of new body cells

As an antioxidant, iodine is also used to protect the thyroid against inflammation and oxidative damage. 

Iodine requirements

The Recommended Dietary Allowance (RDA) for iodine in the United States is as follows:

• 0-6 months: 110 mcg daily (from breastmilk or formula)
• 7-12 months: 130 mcg daily
• Children 1-8 years: 65 mcg daily
• Children 9-13 years: 73 mcg daily
• Children 14-18 years: 95 mcg daily
• Adults: 150 mcg daily
• Pregnancy: 220 mcg daily
• Breastfeeding: 290 mcg daily

Iodine requirements increase during pregnancy since iodine is used for the baby’s brain and neurological development. Babies require iodine from breastmilk, so breastfeeding mothers should ensure an adequate intake of iodine so they and their babies don’t become deficient.

Vegan sources of iodine

Here I’ve listed the vegan-friendly sources of iodine. Some are safer or better sources than others, which I’ll explain in more detail below.

1. Seaweed

Seaweed (marine algae) is the highest vegan-friendly food source of iodine. Commonly consumed types of seaweed include:

• Brown seaweed: Kelp, bladderwrack, kombu, wakame
• Green seaweed: Chlorella, ulva
• Red seaweed: Nori, dulse

Iodine levels in seaweed are considered unreliable since they can vary widely depending on the type of seaweed and the marine environment. 

Levels can vary quite significantly, with the iodine content of commercially available seaweed ranging from 16 mcg per gram to 2,984 mcg per gram¹ of seaweed.

Two tablespoons of dried nori flakes, for example, contain 116 micrograms of iodine.

Brown seaweed falls on the higher end of this range, containing levels of iodine that far exceed the recommended daily limit. For example, a 9-gram serving of kombu contains enough iodine to exceed the tolerable upper intake level by 800%², posing a significant risk for iodine toxicity.

Notably, boiling raw kelp and kombu for 15-30 minutes can significantly reduce their iodine levels as the iodine leaches into the water. If you want to try this method, note that you’d have to boil the seaweed separately, drain the water, and then add the seaweed to whatever dish you’re making.

2. Bread (made with iodate dough conditioner)

Commercially produced bread prepared with an iodate (iodine-based) dough conditioner can be a surprisingly good source of iodine. 

One slice of white or whole wheat bread made with an iodate dough conditioner provides about 140 micrograms of iodine, or almost 100% of your daily needs.

Only about 20% of commercial breads in the US are made with iodate dough conditioner, however, so bread is generally not considered a good source of iodine for Americans. Australia, New Zealand, and Denmark are among some countries that do fortify bread with iodine.

3. Iodized salt

Iodized table salt is one of the most reliable vegan iodine sources. Salt iodization programs exist in the US, Canada, and many other countries. If you’re in the UK, you may have trouble finding iodized salt.

A half-teaspoon of iodized salt contains 156 micrograms of iodine, meaning you can meet the RDA for iodine if you use this amount of iodized salt when you cook throughout the day. 

4. Iodine supplements

Supplements are another option for vegans looking to get enough iodine. They’re often sold in dropper bottles as a liquid. Drops can be mixed with non-dairy milk or juice or blended in smoothies.

Kelp supplements contain toxically high levels of iodine³ and are NOT recommended as a way to get more iodine.

5. Fortified non-dairy products (non-US)

I haven’t come across any non-dairy milks fortified with iodine in the United States, but our friends across the pond may have more luck. 

A 2023 study in the UK⁴ analyzing commercially available dairy alternatives found that 28% of milk alternatives and 6% of yogurt alternatives were fortified with iodine. 

However, since most non-dairy milk and yogurt alternatives aren’t fortified, I wouldn’t consider these products to be a significant source of iodine for most vegans in the UK. 

6. Fruits & vegetables

You may have seen claims on the internet that certain fruits and vegetables are good sources of iodine, but this isn’t true. Some do contain small amounts of iodine, but practically speaking, these levels are negligible. 

There’s no way to meet your iodine needs from produce alone, so fruits and vegetables are not good sources of iodine.

Iodine deficiency

Iodine deficiency is a real risk for vegans who don’t consume seaweed, iodized salt, or iodine supplements. If you’re in the UK and don’t consume iodine-fortified milk alternatives or live in countries that have iodine-fortified bread and don’t consume it, you may also be at risk. 

A 2023 meta-analysis⁵ found that vegan adults had an average iodine intake of 17 micrograms, far lower than the RDA. The study authors concluded that vegans living in countries without universal salt iodization (USI) programs may be particularly at risk of becoming deficient. 

The most well-known sign of iodine deficiency is goiter, while iodine deficiency in infancy can result in impaired brain function and a lower IQ³. 

Over time, severe iodine deficiency can lead to hypothyroidism where the thyroid can’t produce enough thyroid hormone. Symptoms of hypothyroidism can include a slower metabolism and weight gain, fatigue, depression, sensitivity to cold, and joint or muscle pain. It may also increase the risk for thyroid cancer⁶, although more research is needed to confirm this relationship.

RELATED: The 16 Best Vegan Brain Foods

Goitrogens

Goitrogens are compounds thought to interfere with the uptake of iodine into the thyroid and are thought by some to increase the risk of iodine deficiency. Goitrogens are found in foods like soy, broccoli, bok choy, and cassava. 

It’s important to note, however, that goitrogens are most likely only an issue⁷ if you have a low iodine intake or are already iodine-deficient. It makes more sense to focus on meeting the RDA for iodine rather than limiting nutrient-dense foods that contain goitrogens.

Iodine toxicity

The Tolerable Upper Intake Level for iodine is set at 1,100 micrograms per day. Intakes higher than this have been associated with symptoms of toxicity, so it’s best to stay under this amount.

While iodine toxicity won’t directly cause death or symptoms of illness in the short term, consuming high levels of iodine over time can lead to goiter, impaired thyroid function, and a potentially increased risk of thyroid cancer. 

Practical tips for getting iodine as a vegan

Let’s wrap this information up in the form of some helpful tips:  

1. Switch to iodized salt when cooking

This might be one of the simplest swaps you can make to improve the nutritional quality of your diet. Be sure to look for salt with the term “iodized” on the label. Sea salt, Himalayan pink salt, and other specialty salts do not contain iodine unless they’re specifically labeled as “iodized”.

If you’re concerned about the sodium content, keep in mind that a half teaspoon of salt contains only 1,150 milligrams of sodium. This is half of the American Heart Association’s recommended limit of less than 2,300 milligrams, and still less than their “ideal” recommendation of less than 1,500 milligrams of sodium per day.

So for most people, using a half teaspoon of iodized salt every day is a safe way to meet their iodine needs. If you cook most of your meals at home, you’ll likely get this amount of salt in a day.

2. Take a supplement if you don’t cook often or avoid salt

If you don’t like cooking or simply don’t have the time, relying on iodized salt in your meals won’t work very well as a strategy. And unfortunately, packaged foods and pre-prepared meals are rarely made with iodized salt. Additionally, some people following the Whole Food Plant-Based No Oil Diet prefer to completely avoid added salt. 

In these situations, an iodine supplement can be helpful. 

Try to find a supplement with 150 micrograms of iodine as potassium iodide or potassium iodate. If you can only find a supplement with 250 micrograms, taking it four times a week should provide you with enough.

Keep in mind that many multivitamins and prenatal vitamins provide 100% of your daily iodine. Check to see if the supplements you already take contain iodine before adding a stand-alone iodine supplement. 

3. Don’t rely solely on seaweed

Enjoying nori-wrapped veggie sushi or sprinkling a small amount of dried seaweed in soups is a fun, tasty way to get some iodine in your diet, but I don’t recommend relying only on seaweed for your iodine needs. 

As discussed earlier, the iodine content of seaweed can vary drastically, making it almost impossible to know how much you’re actually getting. Brown seaweed like kelp, wakame, and bladderwrack can be extremely high in iodine with the potential to cause toxicity if eaten in excess. Limit these foods to an occasional treat.

For pregnancy and breastfeeding, it’s recommended⁸ to limit brown seaweed to no more than one serving per week.

Summary

It’s entirely possible to get enough iodine to support thyroid function on a vegan diet, so don’t let this be a roadblock to going vegan. Plant-based foods with iodine are few and far between, however, so you’ll need to be intentional about your intake.

The safest, most effective ways for most vegans to meet the RDA for iodine while avoiding toxicity are to:

• Use iodized salt when cooking at home (½ teaspoon provides 100% of your daily iodine)
• Take 150 micrograms of iodine in the form of a daily supplement if you don’t use iodized salt
• Limit your consumption of brown seaweed (kelp, wakame, kombu) to once a week or less. Boiling brown seaweed for 15-30 minutes and draining the water may remove much of the iodine. Eating lower-iodine seaweed like nori in moderation can provide some iodine, but you shouldn’t rely on seaweed for your iodine needs since levels are unreliable.

Interested in other nutrients on a vegan diet? Check out these helpful articles:

The Best Vegan Sources of Selenium

31 Vegan Foods High in Biotin

Vegan Taurine Sources: How Vegans Can Get Enough of This Nutrient

The scientific information in this article was accurate at the time of publishing but may change over time as new research becomes available.

References

1. National Institutes of Health Office of Dietary Supplements. Iodine – Fact Sheet for Health Professionals. NIH website. Accessed 12/28/23.
2. Patel, Kamal. How can I safely consume seaweed? Examine.com website. Accessed 12/28/23.
3. Nicol K, Nugent AP, Woodside JV, Hart KH, Bath SC. Iodine and plant-based diets: a narrative review and calculation of iodine content. Br J Nutr. 2024;131(2):265-275. doi:10.1017/S0007114523001873
4. Nicol K, Thomas EL, Nugent AP, Woodside JV, Hart KH, Bath SC. Iodine fortification of plant-based dairy and fish alternatives: the effect of substitution on iodine intake based on a market survey in the UK. Br J Nutr. 2023;129(5):832-842. doi:10.1017/S0007114522001052
5. Eveleigh ER, Coneyworth L, Welham SJM. Systematic review and meta-analysis of iodine nutrition in modern vegan and vegetarian diets. Br J Nutr. 2023;130(9):1580-1594. doi:10.1017/S000711452300051X
6. Zhou Q, Xue S, Zhang L, Chen G. Trace elements and the thyroid. Front Endocrinol (Lausanne). 2022;13:904889. Published 2022 Oct 24. doi:10.3389/fendo.2022.904889
7. Eastman CJ, Zimmermann MB. The Iodine Deficiency Disorders. In: Feingold KR, Anawalt B, Blackman MR, et al., eds. Endotext. South Dartmouth (MA): MDText.com, Inc.; February 6, 2018.
8. Food Standards Australia New Zealand. Brown seaweed – advice for pregnant women, breastfeeding women, and children. FSANZ website. Accessed 12/28/23.