Iodine is an essential mineral needed for the synthesis of the thyroid hormones, thyroxin and triiodothyronine. Thyroid hormones regulate physiologic processes within cells including physical growth, mental development and the process of converting food to energy. Iodine, in the form of inorganic iodide, occurs in variable concentrations in food.
How Iodine Gets into Food
The largest concentration of the earth's iodine is found in seawater. The iodine level in fish, shellfish and marine vegetables, such as kelp, reflects the iodine content of the waters in which they thrive. The iodine content in soil varies with region and contributes to the variability in iodine levels in plant and animal food sources. Soil erosion leaches iodine from the soil. Mountainous regions, such as the Andes and the Alps, and river valleys prone to flooding, such as the Ganges in India, rank among the world's most severely iodine-deficient areas. Vegetables and legumes grown in iodine-deficient soil have low iodine levels. The soil in coastal regions is strongly enriched with iodine and produce from these areas have higher concentrations of iodine. The iodine levels in meat, dairy products and eggs depends on how the animals were raised. Animals who graze in pastures with low iodine content will produces food sources that are low in iodine. Meat, dairy products and eggs from animals who are raised with iodine fortified feed have a higher iodine content.
Foods with High Iodine Levels.
Marine animals can concentrate the iodine found in seawater, making shellfish a rich source of iodine. Cod, halibut, sea bass, perch and shrimp are examples seafood with high iodine levels. Seaweed, particularly kelp, is a sea vegetable high in iodine. Individuals who live in coastal areas tend to have more seafood in their diet than people living in land-locked regions. Kelp is consumed widely in Japan. Worldwide, iodine deficiency is less common in populations of coastal and island countries. Dairy products, such as milk, yogurt and cheese, are another main source of dietary iodine. Iodine is a widely used and effective germicide in teat dips. Animal feed is commonly fortified with iodine. These two agricultural practices account for the iodine content in meat, dairy products and eggs.
Iodine in Fruits and Vegetables
The iodine content in fruits and vegetables is variable and low in comparison to seafood and animal sources. Iron deficiency is prevalent among vegetarians and vegans, whose diet consists of plant food sources, no fish or seafood and limited or no dairy products. In general, root vegetables, such as potatoes, yams and carrots, cereal grains like rice, legumes including beans, and fruits have low iodine levels.
Inconsistency Leads to Innovation
The inconsistency of iodine content in natural food sources led to iodine deficiency in the general population. In 1821, a French chemist, Jean Baptiste Boussingault, discovered that iodine-rich salt treated a goiter, which is a swelling in the thyroid gland caused by iodine deficiency. It was not until 1924 that iodized salt was commonly available in the United States. Within a decade, the incidence of iodine deficiency significantly decreased with the use of iodized salt. Even today, iodized salt is the most consistent means of getting iodine in your diet. You do not need to use too much salt as there are 400 mcg of iodine in 1 tsp. of salt. The recommended daily allowance for iodine is 150 mcg a day for adults.
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