Iodine from seaweed — safe for the thyroid?

Aim of the study: Globalization has reached the kitchen, and Asian cuisine has become popular around the world, with sushi and seaweed now widely available. We investigated the possible acute adverse effects of an iodine load from a single meal of sushi and seaweed, since iodine in seaweed may cause thyroid dysfunction.

Results: All participants ate the full meal, and none dropped out. No adverse effects were reported. Before the meal, urinary iodine excretion (UIE) was 75 µg/g. UIE rose (p < 0.001) by 385%, 59%, and 43% in groups A, B, and C, respectively. It peaked in the 6-hour urine sample at 393, 120, and 109 µg/g, and had returned to pre-meal levels by day 2. Serum TSH rose (p = 0.012) by 150% on day 2 and returned to pre-meal levels by day 3. Serum fT4 remained unchanged. No adverse reactions were reported. A sushi meal increased urinary iodine excretion by 40 µg/g, or by 400 µg/g if a freshly harvested seaweed salad was added. The resulting rise in serum TSH was brief, and a single sushi meal with seaweed salad caused no adverse events.

Aim of the study: Background: Seaweed is a major source of dietary iodine in Korea, particularly for breastfeeding women in the postpartum period. This practice raises concerns about short-term excess iodine intake and its possible effects on thyroid function.

Results: The prevalence of abnormal triiodothyronine (T3), free thyroxine (FT4), and thyroid-stimulating hormone (TSH) levels was analyzed by quartiles of iodine intake, and no significant differences were found (T3: p = 0.4175; FT4: p = 0.1591; TSH: p = 0.9344). Conclusions: These findings suggest that evidence linking short-term iodine intake after childbirth to thyroid outcomes one year later remains inconclusive. Because of the small sample size, high dropout rate, and observational design, the study may have lacked the statistical power to detect clinically meaningful differences, and possible effects cannot be ruled out. These results should therefore be interpreted cautiously. Larger, well-designed longitudinal studies with repeated thyroid assessments are needed to better clarify the long-term effects of iodine exposure after childbirth.

Aim of the study: Background/Objectives: Seaweed has recently attracted global attention as a sustainable food that promotes health. However, seaweed contains iodine.

Results: All HI values were below 1.0 under MFDS standards, indicating low potential health risks. However, sea tangle had values above 1.0 under EFSA and JECFA standards. Conclusions: These findings highlight the need for iodine intake guidelines and safety regulations tailored to each species, to protect consumers and support global seaweed trade. This study provides a scientific basis for balancing the nutritional benefits of seaweed against the potential risks of overconsumption. It can contribute to national dietary guidelines and provide evidence-based information for navigating international regulations.

Aim of the study: Iodine deficiency is generally recognized as the most common preventable cause of intellectual disability and the most common cause of endocrine disorders (goiter and primary hypothyroidism). Iodine deficiency is particularly critical during pregnancy because it can cause neurological damage during fetal development, as well as during breastfeeding.

Results: The safety of therapeutic iodine doses above the established safe upper limit of 1 mg is evident from the lack of toxicity in the Japanese population, which consumes 25 times the median iodine intake in the United States. No increased incidence of autoimmune thyroiditis or hypothyroidism has been demonstrated in Japan's population. Studies using doses of 3.0–6.0 mg to effectively treat fibrocystic breast disease may reveal an important role for iodine in maintaining normal breast tissue structure and function. Iodine may also have important antioxidant functions in breast tissue and other tissues that concentrate iodine through the sodium-iodide symporter.