Iodine is a nonmetallic trace mineral necessary for the synthesis of thyroid hormones. Iodine deficiencies are the most common cause of preventable brain damage worldwide, according to the Linus Pauling Institute. Iodine deficiencies affect children most, causing hypothyroidism, retardation and cretinism in infants as well as retardation in children and adolescents. Insufficient iodine intake can cause hypothyroidism, goiter, impaired mental function, fatigue, cold intolerance, weight gain and constipation. Most table salts are fortified with iodine in the United States.
Milk
Cows do not naturally produce milk that contains iodine unless it appears substantially in their diet. Nonetheless, milk has become the chief source of iodine in the United States since the 70s, because of the use of antiseptics that contain iodine to clean equipment and udders, as well as feed fortified with iodine. Moreover, fresh, mineral-rich soil often contains iodine that transfers into the plants that sprout therein. Accordingly, even during the summer months, while cows rely more on pasture grazing than feed, milk often contains trace amounts of iodine.
Seaweed
Seaweed and kelp naturally contain the most iodine of any food. According to the Linus Pauling Institute, a single 1/4 oz. of dried seaweed contains as much as 4,500 mcg of iodine -- 4.5 times the recommended daily value -- which can be toxic. As a result, cultures that eat large volumes of seaweed, particularly those in Asia, exhibit high instances of goiter, resulting from inordinate iodine consumption.
Marine Fish and Seafood
Marine fish and seafood naturally contain iodine and can act as effective sources. Cod, canned tuna, scallops and oysters are among those that contain the most iodine. Although marine plant foods contain extremely high amounts of iodine, marine fish and seafood content are considerably more moderate. Therefore, a diet that includes marine fish and seafood likely won't result in iodine toxicity.
References
- The Linus Pauling Institute: Iodine
- "Diet and Risk: Implications for Reducing Chronic Disease Risk"; National Research Council (U.S.). Committee on Diet and Health; 1989
- "Understanding Normal and Clinical Nutrition"; Sharon Rady Rolfes, Kathryn Pinna and Ellie Whitney; 2009
- "The Thyroid Sourcebook"; Sara M. Rosenthal; 2009
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