Kelp (Laminaria) kūn bù · 昆布

Safety. As with sargassum, the iodine is the operative fact. Kelp is one of the most concentrated dietary iodine sources there is, and an intake that is harmless for one person can trigger or worsen thyroid dysfunction in another — both hyperthyroidism and hypothyroidism have been described in relation to high seaweed intake. Anyone with thyroid disease, on thyroid medication, or being investigated for a thyroid swelling should not add kelp on their own; it changes thyroid function tests and can change the course of the disease. Kelp also accumulates arsenic, cadmium and other seawater elements, and content varies by harvest area. A thyroid lump needs a diagnosis first. Being cold, it is traditionally avoided where the digestion is weak and cold. Safety in pregnancy and breastfeeding is not established.