Vegetarian and vegan diets often lack iodine and other essential nutrients

There is a trending global shift towards vegetarian or vegan diets. However, these diets come with a risk of lacking essential nutrients that are primarily found in animal food sources. According to a large meta-analysis of Western diets, one of them is iodine. Iodine deficiency is a worldwide problem and has serious consequences because of iodine’s vital role in the thyroid function, energy production, estrogen balance, fertility, and healthy pregnancy outcome.

Plant-based diets have mainly gained popularity because of the environment but campaigns fail to look at the health aspects involved with cutting out animal foods. It is mostly young people and women who follow the trend. There are different types of plant-based diets. Vegetarians primarily exclude meat and fish, whereas pescatarians don’t mind including fish, shellfish, dairy products, and eggs in their otherwise plant-oriented diets. Also, many people in Western countries choose to go meat-free one or several days a week and refer to themselves as flexitarians. The vegan diet is by far the most stringent eating pattern and excludes any type of animal food. In contrast, an omnivore is someone who eats everything, and this is what humans have been doing since the beginning of time. We can see it by looking at our teeth, our digestive systems, and our metabolism.
The growing interest in plant-based diets has increased the need for replacements such as plant-based milk products, meat substitutes, etc. A whole new food industry has been established and focuses on plant-based, ultra-processed alternatives that try to emulate the real thing in terms of appearance, taste, and texture. This requires the use of coloring agents, hydrogenated plant oils, emulsifiers, taste enhancers, and other additives.
The problem is that plant-based diets often lack essential nutrients. Many people therefore take vitamin B12 supplements, but this is often not enough. Earlier studies show that there is also a risk of being deficient in vitamin D, iron, selenium, iodine, and omega-3 fatty acids (EPA and DHA). According to a new meta-analysis that is published in British Journal of Nutrition, modern plant-based diets often lack iodine, and this may have serious consequences.

Vegetarians and vegans in particular risk lacking iodine

The meta-analysis collected data from several studies published in the period between October 2020 and December 2022 and found on databases like Ovid MEDLINE, Web of Science, PubMed, and Scopus. The authors focused on studies of iodine intake in industrialized countries and ended up with 11 eligible articles, including a total of 4,421 people aged 18 years and older, who ate different types of plant-based diets or were omnivores. The meta-analysis showed the following:

None of the groups had had optimal concentrations of iodine (mUIC) in their urine.
According to WHO, levels should ideally be in the range of 100—200 micrograms/L

• The vegan group had the lowest iodine concentrations in their urine
• The vegan diet contained the least iodine compared to the omnivore diets that had the highest iodine content
• Although both the vegetarians and the vegans ate seaweed, they were often iodine-deficient
• The iodine intake was also related to gender and whether or not people consumed iodine-enriched table salt
• Vegetarians, and vegans in particular, who didn’t eat iodine-enriched salt were most likely to lack iodine

Iodine deficiencies are very common among vegetarians and vegans. The authors point out that there is an urgent need for measuring and adjusting the iodine intake in these high-risk groups. The problem is only made worse by the growing number of campaigns for eating plant-based diets.
Another problem is that many vegetable foods contain goitrogens. When consumed in excessive amounts, goitrogens may affect the ability of the thyroid gland to absorb and utilize iodine. Popular vegetable protein sources like soy and tofu, peanuts, and peanut butter have a high goitrogen content.

Iodine’s role in metabolism, health, pregnancy, and growth

Iodine’s primary role is to help the body make the two thyroid hormones, T3 (with three iodine atoms) and T4 (with four iodine atoms). Thyroid hormones play a vital role in cellular energy metabolism. For this reason, iodine is highly important during pregnancy and supports the growth and neurological development of the child. Studies also suggest that iodine is important for the estrogen balance.
According to WHO, the body needs 150 micrograms of iodine every day. Pregnant and breastfeeding women need 250 micrograms daily to support metabolism, the growth and development of the unborn child, and to prevent deficiency diseases in the mother and the child. Lack of iodine can cause reduced fertility, goiter, hypothyroidism, and even hyperthyroidism in rare cases. Children of iodine-deficient mothers have a risk of stunted growth and mental retardation. Iodine deficiency can even increase the risk of breast cancer.

Iodine deficiency is a global problem

Iodine is primarily found in fish, shellfish, seaweed, and fish sauce. It is also found in eggs and dairy products. Sea salt is unable to cover the need for iodine. In many countries, Denmark included, table salt is enriched with iodine to prevent goiter. Many consumers, however, avoid iodine-enriched table salt if it also contains aluminum (anti-caking agent). Fluoride compounds in the environment can interact with iodine, thereby increasing our need for the nutrient.

References

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

Else Molander. Anbefalinger vedr. vegansk kost. Fødevarestyrelsen. Januar 2019
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