Functions	Iodine plays a major role in the development and function of the thyroid gland. It is a component of the hormones thyroxine and triiodothyronine. These hormones are thought to have a tremendous effect in the control of cellular metabolism. It also increases motility of the gastrointestinal tract, increases reactivity of the nervous system, and increases the hearts efficiency at utilizing oxygen.
Deficiency can cause:	Hypothyroidism. This is when thyroid secretion becomes abnormally low. Symptoms include lethargy, fatigue, extra sensitivity to cold, and dried out skin. Metabolic rates decline, which in turn stimulates the thyroid to produce more thyroxine. If deficient in iodine, this can't take place, and can result in enlargement of the thyroid, which is known as endemic goiter. In infants a condition known as cretinism can result from an iodine deficiency. It's symptoms include constipation, poor appetite, jaundice, and slowed bone growth. Low basal body temperature and weight gain are also symptoms of iodine deficiency.
Toxicity can cause:	Iodine is generally considered non-toxic under 1,000 micrograms. Too much may cause the synthesis of thyroid hormones to be impaired, may increase thyroid secretions (hyperthyroidism). This is characterized by an increase in heart rate, elevated blood pressure, excessive sweating, weight loss, and an intolerance to heat. Other symptoms could include signs of nervousness, agitated behavior, and problems sleeping.
Food Sources:	Seafood, liver, eggs, dairy, asparagus, garlic, lima beans, mushrooms, sesame seeds, soybeans, summer squash, Swiss chard, turnip greens, and iodized salt.
Herbal Sources:	Black walnut, dulse, kelp
R. D. A.	Infants 0 - 0.5               40 mcg. 0.5 - 1 year       50 mcg. Children 1 - 3 years         70 mcg. 4 - 6 years           ?? 7 - 10 years       120 mcg. Young Adults and Adults 11 + years          150 mcg. Pregnant             +25 mcg. Lactating             +50 mcg.

Comments: Foods such as Brussels sprouts, cabbage, cauliflower, kale, peaches, pears, spinach, and turnips can block the uptake of iodine into the thyroid. If your thyroid is under-active you should avoid these foods.

*The Nutrition Desk Reference by Robert Garrison, Jr., M.A., R.Ph. and Elizabeth Somer, M.A., R.D. (Keats Publishing Company, New Canaan, Connecticut) 1995, pp. 196