Quantity of iodine present in foods depends on iodine content of soil. Iodine is added to table salt and people generally get the required amounts from just one teaspoon of iodised salt. Other iodine sources include eggs, milk, sea fish and sea food. Cabbage, cauliflower, radish are considered as goitrogenic foods as they contain toxic constituents (goitrogens) which react with iodine in other foods and make it unavailable to the body.
The iodine content of drinking water is a valuable index of the iodine content of the rocks and soils of a region, and hence of the locally grown foods. Such data has been correlated with the incidence of goiter in many areas.