Kelp

Kelp refers to several species of large brown macroalgae belonging to the order Laminariales, including Laminaria digitata, Laminaria japonica (kombu), and Ascophyllum nodosum. These seaweeds are among the most concentrated natural sources of iodine, an essential trace element required for thyroid hormone synthesis. A single gram of dried kelp can contain 500–8,000 mcg of iodine, far exceeding the recommended daily intake of 150 mcg for adults. Kelp also contains unique bioactive polysaccharides such as fucoidan and alginate, which have demonstrated anti-inflammatory, anticoagulant, and prebiotic properties in preclinical research. While kelp supplementation can effectively address iodine deficiency, the highly variable iodine content between products and even between batches of the same product creates a real risk of excessive iodine intake, which can paradoxically cause both hypothyroidism and hyperthyroidism. Case reports of kelp-induced thyrotoxicosis and hypothyroidism are well documented in the medical literature.