Iodine is an often-overlooked essential mineral. It may be a concern for people eating a vegan diet, therefore it’s a mineral that all vegans should be aware of and know how to consume more of.
It’s difficult to know how much iodine is in vegan foods because, depending on where food is grown, iodine within soil can vary drastically. This, and the popularity of non-iodized salts (like pink Himalayan or sea salt) suggests some vegans may benefit from taking an iodine supplement.
Always speak to your primary care provider before starting new supplements.
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What is Iodine?
Iodine is an essential mineral, which means the body requires iodine but cannot produce any itself. Like any essential nutrient, people must consume iodine through their diet.
Since the introduction of iodized salt, iodine intake in Canada is generally at adequate levels 1.
However, using popular non-iodized salts (sea salt, pink salt, etc.) may lower overall iodine intake. These alternative salts do not contain enough iodine to be of value for preventing iodine deficiency.
Other major sources of iodine are dairy products and seafood, which are foods that vegans don’t consume. Therefore, vegans need to be aware of iodine intake and consume adequate amounts.
What Does Iodine Do in the Body?
Iodine is needed to make thyroid hormones 2.
Iodine is particularly important for pregnant people and infants/ children due to its critical role in growth and development 2.
Daily Intake Requirements of Iodine for Vegans
For people ages 19 years and older, the recommended daily intake of iodine is 150 micrograms per day, according to Health Canada 3.
Women who are pregnant or lactating have different needs. In pregnancy, daily recommended intakes are 220 micrograms per day while during lactation, 290 micrograms per day are recommended 3.
There’s currently no evidence to suggest vegans need to consume different amounts of iodine compared to those eating an omnivore diet.
Therefore, vegans should aim to meet the intake recommendations outlined above.
Iodine deficiency is common across the world.
In adults, iodine deficiency can lead to low levels of thyroid hormones which can cause hypothyroidism 2. There are many other causes of hypothyroidism as well.
- Fatigue/ tiredness
- Intolerance to cold (always feeling cold)
- Weight gain
- Hair loss
- Dry, flaky/ cracked skin
- Weakened immune system
In pregnancy, a limited intake of iodine can cause cretinism 2. This can present in children as a mental and physical disability, and can result in stunted growth, low IQ, deafness and/or muteness.
If you have any symptoms or concerns about low iodine intake and/or hypothyroidism, please speak to your primary care provider as soon as possible.
Are Vegans Deficient in Iodine?
Research supports that vegans often do not consume enough iodine. One study with 15 vegans, 31 vegetarians and 35 omnivores found high levels of deficiency among the vegan and vegetarian diet groups 8.
Iodine deficiency is often assessed using urine, which is a helpful tool to determine recent (but not chronic) iodine intake.
Day-to-day variation of iodine consumption, and output of iodine in urine, can be as much as 30-40 % 6. This is important to consider when interpreting research because several measurements are needed to determine iodine status 6.
Furthermore, there’s debate over the ranges used to determine iodine deficiency from urine iodine concentration measurements 6.
If a study uses high urine iodine concentration values, more people will appear to be deficient in iodine intake.
There is also concern about studies using urine iodine concentration as many do not account for urine volume, which may be higher in vegans (due to higher water content of plant-based foods). Correcting for this, vegans may have higher iodine intake than what is reported in studies 7.
Adjusting for lower concentration levels and higher urine volume, iodine deficiency in vegans may be overreported 7.
Since iodine intake is critical for thyroid health, examining the thyroid health of vegans may also be helpful 7. It seems that vegan diets tend to be associated with lower risk of thyroid disease 15, 16.
While there are valid concerns of how iodine status is measured, without supplementation or seaweed consumption it seems vegans have lower iodine intakes/ urine output compared to omnivores 7.
While iodine is an essential nutrient, more is not always better.
Due to excessive iodine intake concerns, a tolerable upper limit has been set for this nutrient. The upper intake limit for people over the age of 19 is 1100 micrograms of iodine per day 3. This includes iodine from food sources and supplements combined.
Iodine toxicity has been reported in case studies, often in people who have an underlying condition such as thyroid disease, or in infants or the elderly. Supplementation and seaweed consumption have been reported to cause excess iodine intake 17. Certain medications, contrast dyes (for medical imaging) and topical iodine can also be sources of excess iodine exposure 17, 18.
Consuming seaweed, or supplements made from seaweed or microalgae, can put vegans at risk of consuming excess iodine given large variations of iodine in seaweed and supplements 9, 13, 17, 19, 20. Iodine content of seaweed (or supplements made from seaweed or microalgae) can contain toxic amounts of iodine 9, 13, 17, 19, 20.
Risk of iodine excess is relatively small compared to the risk of iodine deficiency which is far more common 4.
Vegan Food Sources of Iodine
On a vegan diet there are two main sources of iodine: iodized salt and seaweed.
Bread, grain products, vegetables and fruits contain highly variable (and generally small) amounts of iodine. The amount of iodine in these foods is unlikely to meet intake needs if iodized salt and/or seaweed isn’t used to supplement the diet.
Iodine content of foods are not reported in the Canadian Nutrient File (a database that reports nutrient content of foods available in Canada) 21. I suspect this is due to the high variability of iodine in foods, meaning standardized amounts cannot be reliable.
Iodine deficient soils are considered “widespread” in Canada 22.
Iodized salt, also known as table salt, is salt with iodine fortification.
A half teaspoon (2.5 grams) of iodized salt per day should be enough to meet intake needs for non-pregnant/ non-lactating adults.
While sodium intake recommendations vary depending on the source, many health organizations target an intake of 2300 milligrams of sodium per day or less 25, 26, 27. There is currently debate over sodium intake recommendations, with some reports suggesting more moderate intake levels to be beneficial (for heart health) 28, 29.
Therefore, using ½ teaspoon of iodized salt can meet iodine intake requirements while keeping sodium intake under recommended levels.
The majority (up to 70%) of excessive salt intake is from pre-packaged, processed foods, rather than adding salt to home cooking 30. Using small amounts of iodized salt in home cooking can help meet iodine needs without exceeding sodium intake recommendations.
Some people may benefit from limiting salt intake. If you have any concerns, speak to a doctor or dietitian about balancing iodine and sodium intake guidelines.
Salt that is not iodized (many sea salts, pink salts, Kosher salts and pickling salts) do not have adequate amounts of iodine. They are NOT considered a source of iodine.
Most of the salt in prepackaged foods (canned goods, frozen meals, other premade meals) is not iodized despite often containing very high amounts of salt/ sodium.
Lastly, some people have concerns over the safety of iodized salt. Iodized salt is considered safe 31 and is typically fortified with potassium iodate 32. Some people may prefer to take an iodine supplement, in which case, speak with your doctor first.
Seaweed for Vegan Iodine
There are two considerations for using seaweed as a source of iodine:
- Iodine levels in seaweed vary greatly, therefore it’s often impossible to know how much iodine you consume 33, 34.
- There may be concern for seaweed and seaweed products to contain high levels of iodine that may be harmful. Seaweed tablets/ supplements also pose potential harm of containing too much iodine and possibly arsenic 33, 34.
Overall, while seaweed can be part of a balanced diet, it may not be the best option for meeting iodine intake requirements.
Bread and Grain Products for Iodine
Most bread products contain very little iodine unless they use potassium iodate or calcium iodate (as a dough conditioner) 35. This should appear in the product’s ingredient list.
Breads that use these iodine-containing dough conditioners are good sources of iodine (about 150 micrograms per slice), but most bread products do not use this ingredient 35.
I’ve seen reference to pasta being a good source of iodine, but this is only true if you cook the pasta in water seasoned with iodized salt 35. After cooking pasta in water with added iodized salt, there is about 38 micrograms of iodine per 1 cup of cooked pasta 35.
Fruits High in Iodine
The iodine content of fruit depends on the soil it’s grown in. I’ve seen reference to certain fruits as being “good sources” of iodine, including strawberries, cranberries, prunes and bananas.
I was unable to find a reliable source to support these claims. Instead, it seems these foods contain very little, if any, iodine 35, 36. On average, one serving of fresh fruit seems to have less than 1 microgram of iodine 36.
Vegetables High in Iodine
Like fruits, vegetables are only a source of iodine if grown in iodine-rich soil. I’ve seen reference to potatoes, green beans, corn, spring greens, watercress, zucchini and kale as being good sources of iodine.
One study found, for an average serving of different vegetables, the iodine content was 1 microgram or less per serving 36. The exception to this was 3 cups of raw spinach with 5.4 micrograms of iodine, and ⅔ cup prepared mashed potatoes with 8.7 micrograms (however, this likely means the potatoes were “prepared” with dairy products) 36.
How to Get Enough Iodine as a Vegan
Eating enough high-iodine foods is only one step to ensure you get enough iodine as a vegan. How much iodine the body can absorb is another factor to consider.
There are naturally occurring compounds in some plant-based foods that contain goitrogens 4, 35, 37. These goitrogens can limit how much iodine gets into the thyroid (iodine must enter the thyroid to make thyroid hormones) 35, 37.
Goitrogens are found in soy, cassava, bamboo shoot, sorghum, millet and cruciferous vegetables (broccoli, cauliflower, cabbage, turnip, radish) 2, 35, 37. Having an iron deficiency or vitamin A deficiency can also impact the amount of iodine taken up by the thyroid 35, 37, 38. Smoking can also limit iodine uptake in the thyroid 2, 4.
A diet that’s very high in goitrogens could enhance iodine deficiency 35. It seems that with adequate iodine intake, consuming foods with goitrogens doesn’t cause issues 35, 37. However, if iodine deficiency is present, consuming these foods can make it worse 35, 37.
Goitrogens seem to be an issue only in areas where iodine intake is very low and where intake of high goitrogen foods makes up a majority of the diet (like in populations who rely on cassava root as a major food source) 2, 37.
Overall, it seems vegans shouldn’t be concerned about consuming foods with goitrogens if there is adequate iodine intake, and they eat a varied diet. Adequate iron and vitamin A status, and not smoking, are also prudent.
Do Vegans Need an Iodine Supplement?
Vegans who don’t use iodized salt and/or don’t consume high iodine foods (seaweed) on a regular basis may need to supplement with iodine 7. Always speak to your primary care provider before starting new supplements.
Without iodized salt, vegans may become deficient in iodine because other high iodine foods (mainly dairy and seafood) aren’t eaten 8, 9, 10, 11, 12, 13. Since it’s difficult to know how much iodine is in fruits, vegetables and grain products, they aren’t a reliable source of iodine 35, 36.
Potassium iodine supplements that aren’t made from kelp may be the best option for vegans looking for an iodine supplement.
Speak with your doctor (or dietitian) to determine the type and dose of iodine supplement that’s best for you. Supplementing up to the daily intake recommendations is likely a good target 7.
Summary: Iodine on a Vegan Diet
Iodine is an essential mineral used to create thyroid hormones. Deficiency and toxicity are both possible (deficiency is much more common) so take care to ensure adequate amounts are consumed, but excess amounts are not taken.
Vegan diets may be low in iodine as high-iodine foods like dairy and seafood aren’t consumed.
Iodized salt is the most reliable way to ensure adequate intake of iodine on a vegan diet. Seaweed is another option; however it may contain levels of iodine that are too high.
Other foods have highly variable iodine amounts and are not considered a reliable source of iodine.
Always speak with a doctor before changing your diet or taking new supplements. Please read our full website disclaimer.
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This reference list is not intended to be comprehensive.
About Nicole Stevens
Nicole is a vegan Registered Dietitian (RD) and founder of Lettuce Veg Out.
She helps people thrive on a vegan diet with balanced recipes and easy-to-understand nutrition science.