From the Guidelines
Patients with thyroid disease should avoid regular consumption of seaweed due to its high iodine content, which can significantly impact thyroid function, as evidenced by a 2018 study published in the Proceedings of the Nutrition Society 1. When considering the consumption of seaweed, it is crucial to understand the potential risks associated with its high iodine levels. The study found that the iodine level in seaweed products is very broad, ranging from 11–6118 µg/g of dried seaweed, which could lead to an iodine excess beyond the European tolerable upper limit of 600 µg daily 1. Some key points to consider for patients with thyroid disease include:
- Seaweed can worsen hyperthyroidism (overactive thyroid) due to excess iodine
- High iodine intake can interfere with the treatment effectiveness of medications like levothyroxine (Synthroid, Levoxyl) for hypothyroidism (underactive thyroid)
- Autoimmune thyroid conditions like Hashimoto's thyroiditis may experience flare-ups with high iodine consumption
- If seaweed is consumed, it should be limited to small amounts (e.g., once or twice a month) and avoided in supplement form, especially concentrated forms like kelp tablets
- The timing of seaweed consumption relative to thyroid medication is important, with a recommended separation of at least 4 hours to prevent absorption interference. It is essential for patients with thyroid disease to consult their healthcare provider before including seaweed in their diet to determine the best approach for their individual condition.
From the Research
Seaweed Consumption and Thyroid Disease
- Patients with thyroid disease should be cautious when consuming seaweed, as it can be a significant source of iodine 2, 3, 4.
- Excessive iodine intake can lead to thyroid function disorders, including hypothyroidism and hyperthyroidism 5, 6.
- Some types of seaweed, such as brown seaweeds (kelps), can have antithyroid actions even in small amounts, and product labeling may be insufficient 2.
- Seaweed supplementation can improve iodine status in iodine-insufficient individuals, but it is essential to monitor thyroid function and adjust intake accordingly 3.
Risks and Precautions
- Chronic, excessive iodine consumption can cause primary hypothyroidism, and a detailed dietary history is crucial in patients diagnosed with primary hypothyroidism without thyroid autoantibodies 5.
- Ingesting large amounts of seaweed, such as "Kombu" (Laminaria japonica), can suppress thyroid function in normal adults, although the effect is reversible 4.
- Patients who are particularly vulnerable to the effects of iodine excess, such as those with autonomously functioning thyroid nodules, should be aware of potential sources of iodine excess, including seaweed 6.
Recommendations
- Universal salt iodization remains the optimum method of achieving optimum iodine status, and promoting increased dietary iodine intake is recommended in young women, in early pregnancy, and in vegan and vegetarian diets 2.
- Regular assessment of iodine status is necessary, even where iodine intake is enhanced, to prevent excessive iodine consumption and related thyroid disorders 2, 3.