Nutrient spotlight: iodine
Iodine deficiency was a problem in North America in the early 1900’s, with low intakes of iodine resulting in high rates of goiter (enlarged thyroid gland). In the 1920’s, manufacturers began voluntarily adding iodine to salt, which significantly reduced the incidence of goiters. This practice continues today.
Lately there has been a lot of attention in the media on sodium intakes. North Americans ingest far more sodium than they need due to the high amount of salt found in processed and restaurant-prepared foods. While adding less salt to our food at home may decrease our risk of hypertension (high blood pressure) from excess sodium, it may also be putting us at risk of iodine deficiency. In addition, many people choose sea salt and kosher salt over iodized due to its culinary popularity, however these salts actually contain very low levels of iodine (unless they are iodized).
Daily requirements of iodine:
Requirements for iodine vary based on age and increase during pregnancy and lactation. The tolerable upper level intake for iodine (for adults) is 1100 mcg/day.
|14 and up||150|
Food sources of iodine:
Naturally occurring iodine in food is rare due to the low levels of iodine found in soil. The richest sources of iodine in our diet are iodized salt and saltwater fish. The iodine content of meat, dairy and eggs varies depending on the iodine in the animal feed. Interestingly, iodine found in dairy products is the result of iodine-based sanitizers that come in contact with the milk. Most processed food items are NOT made with iodized salt (unless it is listed in the ingredients), therefore they are not significant sources of iodine. Note: the recommended daily maximum for sodium (2300 mg) is equal to about 1 tsp of salt.
|Food||Iodine content (mcg)||% DV (adult)|
|Salt, iodized (1/2 tsp)||200||130%|
|Salt, sea (1/2 tsp)||0.19||0.13%|
|Bread, made with iodate dough conditioner, 1 slice||142||95%|
|Bread, made with regular process, 1 slice||35||23%|
|Haddock, 3 oz||104-145||69-97%|
|Cottage cheese (1/2 cup)||26-71||17-47%|
|Cheddar cheese, 1 oz||5-23||3-15%|
|Shrimp, 3 oz||21-37||14-25%|
|Ground beef, 3 oz||8||5%|
DV=Daily Value (based on adult recommended intakes)
Deficiency and toxicity symptoms:
As iodine is required to produce thyroid hormones, iodine deficiency can cause hypothyroidism including goiter (enlargement of the thyroid). Other symptoms of hypothyroidism are: decreased body temperature, sensitivity to cold, weight gain, and fatigue. If a women is deficient during pregnancy, her child is at risk of developing a disorder known as cretinism, which is characterized by low IQ, stunted growth, and sometimes deafness and muteness. Deficiency during pregnancy is also associated with stillbirths, spontaneous abortions, and neonatal death. Moderately low iodine intakes in children has been associated with impaired mental function. Vegetarians and vegans have a greater risk of developing iodine deficiency, especially if they use non-iodized salt in cooking.
Too much iodine (greater than 1100 mcg/day–or about 1 tbsp iodized salt) can block the production of thyroid hormones, also resulting in the formation of a goiter. As you may notice in the table above, some seaweed (such as kelp) contains very high levels of iodine, therefore eating large amounts of seaweed could put one at risk of iodine toxicity.
Teas, J., Pino, S., Critchley, A. & Braverman, L.E. (2004). Variability of iodine content in common commercially available edible seaweed. Thyroid, 14, 836-41.
Thompson, J., Manore, M. & Sheeshka, J. (2010). Nutrition: a functional approach (2nd ed.), Toronto ON, Pearson Education Canada.
Mahan, L.K & Escott-Stump, S. (2004). Krause’s food, nutrition & diet therapy (11th ed.), Philadelphia, Elsevier.