Brown seaweed, particularly species such as Laminaria and Ascophyllum, is often used to support thyroid function due to its naturally high iodine content. Iodine is an essential nutrient required for the synthesis of thyroid hormones (thyroxine/T4 and triiodothyronine/T3). Scientific studies have established that dietary iodine is crucial for normal thyroid function and that iodine deficiency can lead to hypothyroidism and goiter. Brown seaweeds are among the richest natural sources of iodine, with concentrations varying based on species and harvesting conditions.

Clinical evidence directly linking brown seaweed supplementation to improved thyroid health is limited, but there is a clear mechanistic rationale: consuming iodine-rich foods can help prevent or correct iodine deficiency. However, excessive intake of iodine, which can occur with high consumption of brown seaweed, may also disrupt thyroid function and trigger thyroid disorders in susceptible individuals. Therefore, while the use of brown seaweed to support thyroid health has a scientific basis due to its iodine content, more controlled human studies are needed to confirm efficacy and safety regarding thyroid outcomes.

In summary, brown seaweed is scientifically justified to support the thyroid gland primarily due to its iodine content, which is essential for thyroid hormone synthesis, but caution should be used regarding dosage.