Plant-based diets lack iodine

Vegetarian and vegan diets have become very popular – especially among women and younger people – but there is cause for concern, as these plant-based diets often lack a number of essential nutrients. One of them, iodine, plays an important role in metabolism, estrogen balance, and cancer prevention. According to an article published in Frontiers in Nutrition, women of childbearing age, pregnant women, and children are particularly vulnerable. The authors discuss the health benefits of iodine and how much we actually need.

Vegetarian and vegan diets have become fashionable for various reasons. Also, many people have cut back on their meat consumption or combine vegetarian eating with seafood. “Vegetarianism” is therefore an umbrella term that covers a range of dietary patterns but with a strong focus on plant-based foods. As a result of this, the nutrient content of such diets can vary considerably. Compared with omnivorous diets that include both plant and animal foods, vegetarian diets tend to provide more folate, magnesium, potassium, fiber, and antioxidants. However, they often lack vitamin B12, vitamin D, and minerals such as iron, calcium, selenium, zinc, and iodine.
As more and more people turn to plant-based diets, the market has seen a rise in ultra-processed, plant-based meat alternatives fortified with nutrients such as vitamin B12, iron, calcium, or vitamin D. Unfortunately, there is a high risk that plant-based diets lack iodine, which we primarily obtain from fish, shellfish, eggs, and dairy products. Although certain seaweeds (such as dulse, nori, kelp, kombu, and wakame) are sources of iodine, the Danish Veterinary and Food Administration advises against eating seaweed every day, as the high iodine content may be harmful.
Because of widespread iodine deficiency problems in the general population, many countries have introduced iodized salt to prevent goiter. Although sea salt and Himalayan salt contain small amounts of iodine, they do not provide enough to meet our daily needs.
A previous meta-analysis has also shown that iodine deficiency is widespread, especially among vegetarians – and even more so among vegans.

The importance of iodine for metabolism, estrogen balance, pregnancy, growth, and detoxification

Iodine is essential for our metabolism because it is required for the production of thyroid hormones: thyroxine (T4), which contains four iodine atoms, and triiodothyronine (T3), which contains three iodine atoms. We also need selenium to help remove one iodine atom from T4 in order to convert it into active T3. The activity of thyroid hormones plays a crucial role in cellular energy metabolism. However, an increasing number of people now suffer from thyroid disorders such as Hashimoto’s disease, which leads to hypothyroidism.
Iodine is also vital for a child’s growth and neurological development. Pregnant women are therefore particularly vulnerable, as severe iodine deficiency may lead to mental retardation and stunting in the child.
In addition, iodine helps maintain estrogen balance and thereby helps protect against breast cancer. WHO recommends a daily iodine intake of 150 micrograms. Pregnant and lactating women need 250 micrograms per day to support the child’s development and to prevent deficiency disorders. The upper safe intake level is set at 600 micrograms daily.
People with Hashimoto’s disease should not take iodine supplements unless they are adequately supplied with selenium, and professional dietary guidance is advised in such cases.
According to the new article, vegetarians and vegans in particular should pay closer attention to getting sufficient iodine from seaweed or supplements, especially if they avoid fish and shellfish. It is also important to avoid excess intake of iodine, as the content varies greatly between different seaweed types. Excess iodine may cause palpitations, nervousness, sweating, weight loss, and other symptoms of hyperthyroidism.

Iodine content per serving

Note: Concentrations may vary depending on soil conditions, animal feed, and other factors.

Dulse seaweed, dried (10 grams): 1,416 micrograms
Nori seaweed, dried (10 grams) 232 micrograms
Baked cod: 146 micrograms
Yoghurt: 100 micrograms
Hard-boiled egg: 31 micrograms
Pasta cooked with iodized salt: 30 micrograms
Mozzarella: 15 micrograms
Shrimp: 13 micrograms
Baked salmon: 11 micrograms
Chicken breast: 1 microgram
Cucumber and boiled broccoli: 0.4 micrograms
Apple and avocado: 0.1 micrograms
Beans, lentils, and tofu: 0 micrograms
Olive oil: 0 micrograms

References:

Laura Croce et al. Moderne challenges of iodine nutrition: vegan and vegetarian diets. Frontiers in Nutrition 2025.

Elizabeth Rosee Eveleigh et al. Systematic review and meta-analysis of iodine nutrition in modern vegan and vegetarian diets. British Journal of Nutrition 2024

Weikert C et al. Vitamin and Mineral Status in a Vegan Diet. Deutsches Aerzteblatt Online. November, 2020

Frederick R. Stoddard et al. Iodine Alters Gene expression in the MCF7 Breast Cancer Cell Line: Evidence for an Anti-Estrogen Effect of Iodine. International Journal of Medical Sciences. 2008