Iodine is a chemical element essential for the production of thyroid hormones that regulate growth and metabolism. Diets deficient in iodine increase the risk of retarded brain development in children (cretinism), mental slowness, high cholesterol, lethargy, fatigue, depression, weight gain, and goiter: a swelling of the thyroid gland in the neck. Please note that both too much and too little iodine can cause hypothyroidism.
What foods are naturally high in iodine?
Iodine is a component of almost every living plant and animal. No standard measurements of iodine in food exist because iodine concentrations vary across the world. In general, foods from the sea contain the most iodine, followed by animal foods, then plant foods. Of all foods, seaweed (like kelp), is the most well-known and reliable source of natural iodine. Eggs can also be a good source.
The concentration of iodine in these foods can vary widely and this table alongside should be taken as a rough guide only: Foods Containing Iodine
Source: Linus Pauling Institute Article on Iodine