Vegan Sources of Iodine – Foods, Supplements, Deficiency
July 1, 2021
Iodine is an essential trace element that supports the production of thyroid hormones. These hormones play roles in regulating the body’s metabolic rate, ensuring normal growth and development of tissues and help the body mature.
Iodine is richest in seafood and bread. Unfortunately, there are limited vegan sources of iodine. This means that those following a plant-based diet need to be conscious about meeting their needs.
This article discusses the role of iodine in the diet, how much we need and whether we should consider supplementation.
Iodine and The Thyroid
Iodine is needed for the synthesis of thyroid hormones. 70-80% of the body’s iodine is located in the thyroid gland.
A hormone known as thyroid stimulating hormone (TSH) is the central regulator of the thyroid.
TSH is produced from the pituitary gland. This is a small, bean-shaped gland located in the brain.
TSH regulates how much the thyroid makes of triiodothyronine (T3) and thyroxine (t4), two thyroid hormones. This helps to protect the body against thyroid dysfunction known as hypothyroidism (low thyroid function) or hyperthyroidism (high thyroid function).
When TSH is released from the pituitary gland it tells the thyroid to absorb iodine and create and release T3 and T4.
The thyroid hormones are important for our body as they contribute to (1,2):
- Proper control of the metabolism
- Cell production
- Hormonal balance
- Heart, muscle and digestive system function
- Central nervous system and bone development for infants and foetuses
- Intellectual function for children
Uptake of iodide may be inhibited by goitrogens (substances that exist naturally in food, explained below)
Selenium is also important in iodine metabolism. This is due to its presence in one enzyme that helps to form the thyroid hormones.
Maximising Iodine Absorption
Some foods contain chemical components that act to block the uptake of iodine into our bodies (1).
Goitrogens are a type of compound found in some raw green leafy vegetables. These interfere with the synthesis of thyroid hormones by impairing the binding of iodine.
Sweet potato and corn contain chemicals that compete for the same receptors as iodide (iodine when bonded to another element), blocking the uptake by the thyroid (1).
Examples of foods that inhibit iodine absorption include:
- Raw cruciferous vegetables (cabbage, broccoli, brussel sprouts)
- Sweet potato
- Corn/maize products
Goitrogens are inactivated by heating or cooking.
Eating these foods does not seem to be an issue unless they are consumed in large amounts of combined with iodine deficiency. Goitrigens can worsen an iodine deficiency or contribute to a goiter developing.
The upper limit for adult males and females is 1100mcg per day.
In some cases goiter develops slowly as a consequence of long term iodine intakes that are much higher than the body needs.
The role of excessive iodine in thyroid disease or disorder is not clear. For a small group of people with underlying thyroid conditions, excessive iodine in the diet may result in hypothyroidism, the formation of a goiter or hyperthyroidism.
There has been incidences where products containing toxic levels of iodine has contributed to thyroid conditions. Such as in the case of Bonsoy soy milk which was fortified with toxic levels of iodine. It contained 6250mcg of iodine per cup – 5 times the upper limit. Bonsoy has now been reformulated.
How Much Iodines Do Vegans Need?
Iodine requirements are the same for vegans and non-vegans. It is important to note however, that women who are pregnant or lactating have higher iodine requirements.
Vegan Sources of Iodine
In Australia, iodine is a mineral most readily found in the sea. Iodine requirements are met without effort for vegans that eat nori, kombu, or wakame types of seaweed.
For those that don’t, iodised salt is the next best source.
While there can be small amounts of iodine in various fruits and vegetables, exact quantities cannot be determined.
This is due to the iodine content of foods heavily reliant on the individual soil that they are grown in (1). In Australia, most soil is iodine poor resulting in minimal amounts.
How Do Vegans Eat Enough Iodine?
It can be confusing to understand how to make sure you’re meeting your iodine needs each day. The day on a plate meal plan below, can help make sure you meet your iodine needs as a vegan.
Day on a plate
Breakfast: approx. 39μg
2 slices bread/toast (not organic) (84g) + ½ a med avocado + ½ med tomato + 30g of hemp seeds + squeeze of lemon juice
Lunch: approx. 190μg
2 rolls of vegetable sushi (with cucumber, carrot and avocado – 200g) with low sodium soy sauce
Vegan miso soup (including 1tsp miso paste)
Dinner: approx. 65μg
Mediterranean vegetable fettuccine (with 2 cups mixed vegetables roasted with ¼ tsp iodised salt)
1 med banana + ¼ cup plant-based yoghurt + 30g almonds.
Iodised Salt and Risk of High Blood Pressure
Consuming too much salt (or sodium) is linked to a range of health conditions. These include hypertension (high blood pressure), heart failure and renal disease.
For optimal health, it is recommended to limit sodium intake below 2000mg per day. With this said, sodium is still needed to perform a range of biochemical reactions such as maintenance of blood plasma and cell production.
Consuming ¼ teaspoon of iodised salt equates to 575mg sodium with 65μg of iodine, just under half the daily iodine requirement for an adult. It is important to monitor salt levels of your diet, especially if you have a chronic condition. However, consuming iodised salt will certainly help you meet your iodine needs (6).
Signs of Iodine Deficiency
Iodine deficiency has many negative effects on growth, development and thyroid metabolism. It is also one of the most common causes of preventable intellectual disability in the world (7).
This is especially important during pregnancy and infancy as iodine deficiency can cause irreversible effects.
Iodine deficiency disorders result from inadequate thyroid hormone produced as the result of inadequate iodine.
Whilst mild iodine deficiency is somewhat prevalent in Australia, severe deficiency can lead to conditions such as hypothyroidism.
Hypothyroidism is frequently accompanied by goiter.
When the body does not have enough iodine, TSH levels remain high. This causes the the development of a condition known as a goiter. A goiter is the enlargement of the thyroid gland. This is produced as the body attempts to trap more iodine in the thyroid from the circulating blood and produce thyroid hormones.
This is one of the earliest signs of iodine deficiency.
Symptoms of hypothyroidism include:
- Dry skin
- Hair loss
- Increased sensitivity to the cold
- Weight gain
- Decreased fertility rate
- Muscle weakness and stiffness
Additionally, very severe iodine deficiency (below 30μg/day) during pregnancy can lead to a condition called cretinism in infants and children.
Are Vegans At Risk of Iodine Deficiency
No, not just vegans are at risk of developing an iodine deficiency. Iodine deficiency has been a global concern for over 100 years. In the 1920’s, iodised salt was introduced as a way to increase the population’s iodine intake.
Moving forward to the early 2000’s, studies showed nationally that Australians are still not getting enough iodine, regardless of being vegan or not.
Food Standards Australia and New Zealand (FSANZ) made a decision that from 2009, all bread on the market (with the exception of organic bread) was to use iodised salt as their bread conditioner (2,3) to help boost iodine levels nation-wide.
Groups Most At Risk Of Iodine Deficiency
- People who don’t use iodised salt
- Pregnant women
- People who have limited seafood
- People living in areas with iodine-deficient soils
- People who have a large intake of goitrogens
How Do I Know If I Have Iodine Deficiency?
You may experience iodine deficiency without having any symptoms.
The best way to access your iodine levels is through a urine test ordered through your doctor. Your doctor may also wish to do a blood test to check your thyroid levels, due to the link between iodine and thyroid.
If you have a visible sign of deficiency such as a goitre or enlarged thyroid gland, your doctor may order an ultrasound to measure the shape, size and texture of the thyroid. (8)
Do Vegans Need and Iodine Supplement?
While it’s completely attainable to meet your needs following a vegan diet, there may be some instances where an iodine supplement may assist. This may include pregnant or breastfeeding mothers with higher requirements.
If you also do not regularly consume vegan sources of iodine, it may be beneficial to consider iodine supplement. Before starting a supplementation regime, it’s best to speak to your dietitian to have supplement plan that is individualised to you.
This blog was co-written by PNW Clinic founder Kiah Paetz and student dietitian by Leanna Fyffe. You can connect with Leanna on Linkedin.
If you’re following a plant-based or vegan diet and want to make sure you’re meeting all your nutritional needs, take control and book in to see one of our expert vegan dietitians.