Iodine is an essential nutrient used by the thyroid gland to make thyroid hormones. Those hormones help regulate growth, development and metabolism. Iodine needs are met through foods and, in some places, iodised salt; sources vary by region and diet.
Both too little and too much iodine can cause problems. Seaweed and high-dose supplements can contain large or variable amounts, so they are not a universal solution. Thyroid conditions and medicines can change what is safe.
This is general education, not a dosing protocol. If you are concerned about iodine, thyroid health or a possible deficiency, ask a qualified health professional about assessment and appropriate sources.