Watch the Iodine: Vegetarians Found More Prone to Hypothyroidism, Study Shows

The research, led by Dr. Catharina J. Candussi from the Center for Public Health at the Medical University of Vienna in Vienna, Austria, explored whether dietary patterns, particularly plant-based diets, could influence the likelihood of developing hypothyroidism, a condition marked by reduced thyroid hormone production.

The study assessed six distinct dietary groups: high meat-eaters, low meat-eaters, poultry-eaters, pescatarians (fish-eaters), vegetarians, and vegans. During a median follow-up period of nearly 13 years, 10,831 participants developed hypothyroidism.

The study findings were as follows:

• Initial analysis without adjusting for BMI showed no significant difference in hypothyroidism risk across dietary groups.
• After adjusting for BMI, vegetarians were found to have a 23% higher risk of developing hypothyroidism compared to high meat eaters (HR: 1.23).
• Vegans did not exhibit a significantly elevated risk of hypothyroidism in the adjusted analysis, though their sample size was small (n = 397).
• There was no statistically significant increase in incident hypothyroidism among pescatarians.
• At baseline, there was a higher prevalence of hypothyroidism among pescatarians, vegetarians, poultry-eaters, and low meat-eaters.

The research adds nuance to the growing conversation around plant-based diets. While these diets are widely praised for reducing the risk of heart disease, diabetes, and certain cancers, they may lack critical micronutrients such as iodine, which is essential for normal thyroid function. In regions without mandatory salt iodization, individuals following vegetarian diets may be particularly vulnerable to iodine deficiency. Additionally, some plant-based foods like cruciferous vegetables and soy can interfere with iodine absorption due to their goitrogenic compounds.

“These results highlight the importance of monitoring iodine intake, especially among people consuming less or no animal products,” the authors note. They emphasize the need for further studies that include detailed nutritional assessments and direct measurement of iodine status and thyroid hormone levels.

As plant-based diets continue to gain global traction for both health and environmental reasons, the study underlines the importance of nutritional balance. Healthcare providers may consider routine screening for thyroid function in vegetarians and vegans, especially in populations with low iodine intake.

"Overall, while vegetarian diets offer many benefits, this study underscores the need for awareness around potential micronutrient deficiencies and their long-term health implications," the authors concluded.

Reference:

Candussi, C.J., Bell, W., Thompson, A.S. et al. Risk of hypothyroidism in meat-eaters, fish-eaters, and vegetarians: a population-based prospective study. BMC Med 23, 269 (2025). https://doi.org/10.1186/s12916-025-04045-7