Iodine
The trace mineral iodine is an integral component of the thyroid hormones. Found primarily in sea life, iodine is absorbed into the body through the consumption of sea vegetables and seafood, such as fish and shellfish, and iodized table salt. Other foods, such as beans, nuts, seeds, and vegetables (peppers, spinach, chard, summer squash, turnip, onion, garlic), are good sources, provided that the soil contains sufficient quantities of iodine. Dairy and eggs will contain appreciable quantities of iodine depending on the dietary sources provided to the animals in question.
Concern about iodine deficiency leading to goiter resulted in the fortification of table salt with iodine in 1924 in the state of Michigan. Today, consumption of one gram of iodized salt provides 76 ug of iodine, while sea salt also contains iodine but in lesser amounts. Some bakers may add iodine to dough as a stabilizing agent, rendering up to 150 ug per slice.
Iodine is absorbed quickly through the skin or intestinal tract. On average, 30% is absorbed by the thyroid gland, depending on need, where it is incorporated into thyroid hormones. Iodine is also found in the salivary glands, breasts, choroid plexus, and gastric mucosa. Excess iodine is excreted in the urine or the sweat, tears, and bile.
There have been no reported cases of iodine toxicity from naturally occurring sources in food or water. The RDA of iodine is 150 ug for an adult male.
Iodine deficiency has been known to cause hypothyroidism. It has been associated with increased cholesterol levels, atherosclerosis, fibrocystic breast disease, and breast cancer. Iodine deficiency can also be devastating to the developing brain, causing a mental retardation known as cretinism. Most developed countries, therefore, screen for hypothyroidism at birth.
Large amounts of concentrated iodine taken orally can cause metallic taste, burning mouth, increased salivation, headache, edema, acne, and gastric upset. Prolonged use can cause thyroid gland hyperplasia, thyroid adenoma, and hypothyroidism. Topically, iodine may stain skin, irritate tissues, and cause iodine burns in concentrations of 7% or more. Elemental iodine in the form of potassium iodide has been prescribe in very high doses such as 50 mg per day, with excellent results in terms of decreasing need of t4 in hypothyroid patients, and decreasing hypothyroid symptoms.2 However doses at this high dose can potentially cause side effects such as skin outbreaks and palpitations and aggravations of thyroid nodules. In one study, potassium iodide, along with T4 therapy, inhibited and prevented the growth of thyroid benign nodes in approximately 66% of patients.3
Selected Clinical Studies and Literature Reviews
For a comprehensive review of iodine deficiency research and thyroid disorders, see Guy E. Abraham , Jorge D. Flechas, and John C. Hakala, “Orthoiodosupplementation: Iodine Sufficiency of the Whole Human Body,” in Selected Clinical Studies and Literature Reviews, pp. xx-xx.
