Iodine is a trace element -- an element required in minute amounts for good health. Iodine deficiency is a health concern throughout much of the world as iodine content in the soil varies with region. In older, exposed soil surfaces, large portions of the iodine are often leached away. Most of the earth's iodine is found in oceans. Deficiency is overcome by consuming iodine-rich foods, or supplementing with iodized salt.
Recommendation
The Institute of Medicine recommends that adolescent and adult males and females consume 150 micrograms of iodine daily. Pregnant and breastfeeding mothers should consume 220 and 290 micrograms each day, respectively. Infants up to age 6 months should have an intake of 110 micrograms daily, while babies ages 7 to 12 months need 130 micrograms each day. Children ages 1 to 8 should have an intake of 90 micrograms daily, while those ages 9 to 13 should have an intake of 120 micrograms every day.
Functions
The main function of iodine is as a component of the thyroid hormones triiodothyronine, or T3, and thyroxine, or T4. In the body, T4 is converted to the metabolically active form T3, which regulates gene expression and subsequently regulates metabolism, growth and reproductive function. Thyroid hormones are produced in the thyroid gland and conversion of T4 to T3 is dependent on selenium-containing enzymes. Iodine is also essential for fetal and infant development, especially cognitive development.
Deficiency
The earliest sign of iodine deficiency is goiter, or thyroid enlargement, which is the gland's response to inadequate iodine in the blood. If iodine deficiency is prolonged, hypothyroidism results which is associated with a host of symptoms including fatigue, depression, cold intolerance, muscle cramps, low body temperature and irregular menstrual cycles. Iodine deficiency in the fetal and infant stages can cause mental retardation and growth abnormalities.
Sources
Seafood is the main source of iodine in the diet, particularly fish such as cod and shrimp, and edible seaweed. Dairy is also a source of iodine because it is routinely added to livestock feed. Terrestrial plants, such as beans and potatoes, can be sources of iodine depending on the iodine content of the soil in which they are grown.
References
- "Dietary reference intakes for vitamin A, vitamin K, boron, chromium, copper, iodine, iron, manganese, molybdenum, nickel, silicon, vanadium, and zinc"; Food and Nutrition Board, Institute of Medicine; 2001
- "Oxford Handbook of Clinical Medicine, 5th Edition"; M. Longmore et al.; 2001
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