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Do Vegans Need to Dine on Iodine?

Do Vegans Need to Dine on Iodine?

By Natalie Pape, MA RDN

As vegans, there are certain nutrients we know to pay special attention to. Iodine may or may not be on your radar, but there is evidence that it should be. Do you dine on enough iodine? Here’s what you need to know about iodine as a vegan.

What Is Iodine?

Iodine is an important mineral that is a crucial component of two thyroid hormones triiodothyronine (T3) and thyroxin (T4). To form T3 and T4, your thyroid gland (found in the lower part of the throat) takes up iodine and combines it with the amino acid tyrosine. Only a tiny amount of iodine is needed, but it is critical for health. When iodine intake is too low, we cannot make enough thyroid hormones, and this leads to all kinds of shenanigans. These hormones are essential for energy metabolism, regulating cellular oxygen utilization, and protein synthesis.

Without sufficient iodine, thyroid hormone levels dip, which causes the pituitary gland in the brain to release more of a hormone called thyroid-stimulating hormone (TSH) in an attempt to, well…stimulate more thyroid hormone (the scientists really nailed the nomenclature with that one). If this goes on for too long, the thyroid gland gets a little desperate. Kind of like that bro who overcompensates by puffing up his chest to appear bigger in the hopes of attracting a mate, the thyroid gland becomes enlarged (forming a goiter) in an attempt to physically trap more iodine.

A deficiency in iodine can result in hypothyroidism, which slows down your metabolism, can cause skin and hair problems, weight gain increased cholesterol, fatigue, depression, and feeling cold. Luckily, deficiency can be reversed simply by increasing iodine intake. If you are pregnant, however, an iodine deficiency is seriously risky: even a mild deficiency can permanently impair cognitive ability in a developing baby. (Equally at risk is the fragile ego of that puffy-chested bro, but there is no known cure for that.)

Confusingly, excessive iodine intake can cause many of the same symptoms as a deficiency, like a goiter; when the thyroid gland produces too much thyroid hormone, it can cause the thyroid to become inflamed and swell. Although iodine toxicity is much less common than a deficiency, going beyond the Upper Limit (UL) can be dangerous; it can lead to both hyperthyroidism or hypothyroidism, pain in the mouth, throat, and stomach, fever, nausea, vomiting, diarrhea, weak pulse, and coma: don’t overdo iodine folks!

Dietary Sources of Iodine

Our bodies do not produce iodine on their own, so we need to get it from our diet. However, iodine is found regularly in only a few foods. The most common sources in many diets come from a few animal foods: fish and shellfish, dairy products, and eggs. Vegan sources include iodized salt, seaweeds, and, to a much smaller extent, fruits and veggies that happen to be grown in iodine-rich soil and bread products that may use iodate dough conditioner. Side note: You may see “iodate” or “iodide” listed in some products or supplements. Iodine is usually ingested from food as an iodate or iodide compound, is rapidly absorbed in the intestine, and is then reduced to iodine for use by the thyroid.

Salt: Iodine deficiency in the United States used to be much more common before the 1920s until manufacturers started fortifying salt to prevent deficiencies in the general population. Many countries mandate all table salt to be iodized, but it is optional in the United States where only about 70 percent of salt is iodized. Even so, more than two-thirds of the salt consumed in the United States is from food processing and fast food, most of which is not iodized. While the fortifying strategy worked to curb health problems, deficiency remains an issue for those who do not consume iodized salt or lack other sources of iodine.

Many vegans enjoy sea salt, but unless it is fortified with iodine, sea salt loses any naturally occurring iodine in the drying process. Vegans who use non-ionized salt should be sure to include a reliable source of iodine. The risk for deficiency and hypothyroidism may be increased among vegans who choose non-iodized sodium sources like sea salt, soy sauce, tamari, Bragg’s liquid aminos, and miso.

Many people need to be aware of their sodium intake if they are at risk for conditions like hypertension. Athletes, however, may need more sodium than is recommended for otherwise sedentary people and can ensure adequate iodine status by regularly using iodized salt in cooking and baking. It just so happens that a half teaspoon of iodized salt gives you the Recommended Daily Allowance (RDA) of iodine and gives you 1,163 milligrams of sodium- the approximate amount found in a liter of sweat. Perfect for us sweaty vegan athletes!

 

Seaweed: Iodine mostly comes from the ocean, so seaweeds can be rich sources of iodine. However, the amount can vary greatly from batch to batch (as much as an eightfold difference!) depending on where the seaweed was grown and how it was dried and stored. Iodine is higher in seaweed grown near coral reefs, for example.

Certain seaweeds like kelp and hijiki, are rich in iodine- but be cautious with these. Since iodine can vary greatly in kelp, even regular, moderate intakes can easily push you above the upper limit. In a study including 62 vegans in the Boston area, researchers found that though some were at risk for iodine deficiency because the majority did not ensure a regular source of iodine, one actually had an excessive iodine intake due to a high amount of kelp in their diet. Excessively high iodine intakes have been reported in vegans who regularly consume seaweed in other studies, including a study of raw vegans -Boiling or heating seaweed can reduce or eliminate most of the iodine, so a toxicity issue may be more likely with the raw stuff. It is advisable to limit or avoid hijiki altogether because it commonly contains excessive amounts of arsenic. Seaweeds like wakame and nori, the seaweed traditionally used to wrap sushi, do not pose a significant concern due to relatively low iodine concentrations…is anyone else suddenly craving avocado and sweet potato rolls?

Fruits and Veggies: For land crops, iodine content is going to vary greatly based on location and will depend on how much iodine is retained in the soil, the farming methods used during production, and the season it is grown in. Studies suggest risk for low iodine status is higher in areas where there is lower iodine content in the soil. In North America, we have reasonable iodine content, but many European countries have lower levels. Even if plants are grown in iodine-rich soil, iodine levels in produce are not usually known which makes it difficult to determine intakes. Even so, the iodine content of fruits and land veggies tends to be much lower when compared to other foods (again, these amounts will vary greatly):

 

Food, serving size Iodine Content (mcg)
Seaweed, 1g 16-3,984 (a CRAZY range!)
Cod, 3 oz (90 g) 99
Iodized salt, ¼ tsp (1 ml) 71
Milk, reduced fat, 1 cup (250 ml) 56
Yogurt, plain, ½ cup (125 ml) 37
Egg, 1 large 24
Canned tuna, 3 oz (90 g) 17
Dried prunes, 5 13
Cheddar cheese, 1 oz (30 g) 12
Lima beans, ½ cup (125 ml), boiled 8
Green peas, ½ cup (125 ml), boiled 7
Banana, 1 medium 3

 

A Word on Dairy: Among non-vegans, dairy products can be significant sources of iodine and I would argue they, along with fish and seafood, may be what makes iodine intake and status higher in omnivores than in vegans (see more about the research below). But it is not like dairy is a natural source of iodine, or necessary for healthy iodine levels. While dairy products usually do contain iodine (in unpredictable, varying amounts), this is because cows either receive iodine supplements in their feed, or the cows and machinery are cleaned using iodine-containing sanitizing agents where the iodine seeps into the milk. These cleaning solutions are used to remove mastitis-related pathogens from equipment and cows’ teats. Yum! Plant milks fortified with iodine have an iodine content similar to that of cow’s milk, but few are actually fortified, so check labels. A bonus to the plant-milks that fortify with iodine is they are sourced from plants that are naturally teat and mastitis-free!

Does Eating Broccoli Mess Up My Thyroid?

It should be noted that certain foods can trigger thyroid problems IF a person is deficient in iodine or has a thyroid condition. Soybeans, flaxseeds, peanuts, pine nuts, peaches, pears, strawberries, millet, sweet potatoes, spinach, green tea, and cruciferous vegetables have what are called goitrogenic compounds: isoflavones in soy foods, or thiocyanates in flax and cruciferous veggies for example. The body converts what are called cyanogenic glycosides into substances that can block the uptake of iodine by the thyroid gland. These can interfere with thyroid metabolism when iodine intake is insufficient, or in someone who has thyroid disease.

There are other nutrients worth a mention here when talking about thyroid health. We need to make sure we are getting enough selenium since it is necessary for thyroid hormone production. Vitamin A and D, iron, and zinc are also necessary for thyroid function. If you are having a problem with your thyroid you may have a compromised ability to absorb vitamin B12.

So, does this mean our inner child triumphs and we shouldn’t eat our broccoli? Of course not! We just need to be sure we are getting enough iodine. Healthy people do not need to avoid these nutritious foods at all! Some people with thyroid disease may need to moderate their intake but do not need to completely remove goitrogenic foods; steaming and cooking removes goitrogenic compounds. Other processes such as fermentation, like when cabbage is turned into kimchi, gets rid of thiocyanates; studies suggest thiocyanate intakes are not associated with thyroid problems in vegans. Interestingly, goitrogens can actually be protective for those who consume excess amounts of iodine due to a diet high in seaweed. Many dishes, like in traditional Japanese cuisine, combine seaweed with foods with higher goitrogen content such as soybeans, broccoli, and bok choy. Now I’m craving miso soup along with those veggie rolls.

Vegans and Iodine Research

Vegans can be low in iodine, which as we discussed, is an essential trace element needed for thyroid function and metabolism. For example, a study conducted in Slovakia found that 80 percent of vegans and 25 percent of vegetarians were found to be deficient in iodine compared to 9 percent of those on an omnivore diet. In the Boston study mentioned above, only a third of the vegans included consumed adequate iodine. Iodine intakes have been low in Danish, Norwegian, German, Finnish, and British vegans. A 2020 systematic review agrees with findings from previous systematic reviews that: “vegans [and vegetarians] living in industrialized countries, not consuming seaweed or iodine-containing supplements, appear to have increased risk of low iodine status, iodine deficiency and inadequate iodine intake compared to adults following less restrictive diets.” (Restrictive? HA. Have you seen Dani’s recipes?!)

 

In the most recent (as of this writing) research out of Germany, scientists looked at both blood and urine samples of 36 vegans and 36 omnivores to compare vitamin and mineral status. They found significantly lower urinary iodine excretion in vegans compared to non-vegans (if you are excreting less iodine, this means your body is trying to hold onto it, so a super low excretion level is not ideal). Most alarmingly, in one-third of the vegans, iodine excretion was lower than the World Health Organization (WHO) threshold value for severe iodine deficiency. However! Most of the omnivores had low iodine excretion as well; it was far below the cut-off value for undersupply of iodine in three-quarters of the omnivores and almost all vegans (and this corresponded to low dietary intakes as seen in food diaries). Not too surprisingly, only 5 of the 36 vegans supplemented with iodine (*ahem* you may guess what my recommendation will be for ensuring a healthy iodine status). All in all, out of all 72 study participants, only 8% of vegans and 25% of omnivores achieved a normal iodine excretion status, suggesting it is not only vegans who need to be mindful of this mineral! But as seen with other research, there is reason for vegans to pay special attention. The researchers conclude: “it is challenging to ensure adequate iodine intake in vegans as there seems to be a lack of awareness of this potential deficiency.” Well, lucky you! You’re reading this article and can now dub yourself one of the well-informed. Which brings us to…

Recommendations

The adult RDA (Recommended Daily Allowance) for iodine is 150 mcg per day. Excess amounts can be toxic, so the upper limit (UL) is set at 1,100 mcg of iodine per day for adults (unless otherwise prescribed) and 900 mcg for teens. If you are pregnant, the RDA for iodine is 220 mcg per day with the same upper limit of 1,100 mcg.

 

Either take a multivitamin-mineral supplement that contains iodine or consume about ½ teaspoon (3g) of iodized salt for the daily recommended intake for adults of 150 mcg of iodine. Avoid the use of supplements providing more than the upper limit and be sure to choose products that are third-party tested for dosing and quality. And as always, consult with your healthcare provider.

 

Vegan Dietary Sources of Iodine Portion to get 150 mcg (RDA) Portion to get 1100 mcg (Upper Limit)
Iodized sea or table salt (check the label!) ½ tsp (3 g) 4 tsp (20 g)
Non-iodized sea or table salt NOT A SOURCE OF IODINE NOT A SOURCE OF IODINE
Arame ½ tsp (2 g) 1 1/5 Tbsp (18 g)
Dulse ½ tsp (2 g) 3 1/3 tsp (16 g)
Kelp Less than 1/16 tsp (0.3 g) 0.4 tsp (2 g)
Nori 1 ½ sheets 10 ½ sheets
Wakame 1 1/8 tsp (6 g) 2 ¾ Tbsp (40 g)

 

You can sprinkle seaweeds like dulse or arame into dishes like soups, use wakame for a seaweed salad, or use nori in sushi or wraps. Just be aware that using seaweeds for the occasional dish may not give you the iodine you need if you don’t regularly consume a supplement or iodized salt in your meal prep. And as mentioned above, if you regularly eat seaweed multiple times a week, you could be taking in excessive amounts, as iodine from seaweed is so variable.

Bottom Line

Iodine is an essential nutrient that should not be overlooked. While low iodine is not an issue only for vegans, without direct sources of iodine from a supplement, iodized salt, or sea vegetables, iodine intakes from a vegan diet may be about 10 percent of recommended levels. Vegans need to make sure to get enough iodine, but not too much! So, while you can potentially dine on iodine by using the few food sources available, vegans may want to consider including iodine as part of their supplement regimen to get a reliable and adequate amount daily.

 

Sources

  • Ahad F, Ganie SA. Iodine, Iodine metabolism, and Iodine deficiency disorders revisited. Indian J Endocrinol Metab. 2010;14(1):13-17.
  • Brantsæter AL, Knutsen HK, Johansen NC, Nyheim KA, Erlund I, Meltzer HM, Henjum S. Inadequate Iodine Intake in Population Groups Defined by Age, Life Stage and Vegetarian Dietary Practice in a Norwegian Convenience Sample. Nutrients. 2018 Feb 17;10(2):230. DOI: 10.3390/nu10020230. PMID: 29462974; PMCID: PMC5852806.
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  • Rogerson D. Vegan diets: practical advice for athletes and exercisers. J Int Soc Sports Nutr. 2017;14:36. Published 2017 Sep 13. doi:10.1186/s12970-017-0192-9
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