Iodine is a good example of a trace mineral whose deficiency creates a disease that is easily corrected by resupplying it in the diet. Goiter, an enlargement of the thyroid gland, develops when this important metabolic gland does not have enough iodine to manufacture hormones. As it increases its cell size to try to trap more iodine, the whole gland increases in size, creating a swelling in the neck. Without supplemental iodine, a hypothyroid condition results, likely leading to fatigue and sluggishness, weight gain, and coldness of the body; at this stage, the condition may be harder to treat with iodine alone and thyroid hormone supplementation may be needed.
Goiter was first noted in the Great Lakes region; the “goiter belt” included that area and the midwestern and Plains states. In the 1930s, approximately 40 percent of the people in Michigan had goiter, due mainly to iodine-deficient soil; glacier melting had washed away the iodine. Areas by oceans or in the vicinity of ocean breezes usually contain enough iodine to prevent goiters. In 1924, iodine was added to table salt, a substance that was already in wide use (our salt problem has been going on for a long time). Iodized salt was first introduced in Michigan; by 1940, it was in general use. Even today, iodine deficiency is still a problem, and many people in the United States have goiter. Cretinism, another condition caused by iodine deficiency, is characterized by mental retardation and other problems. It may be present in iodine-deficient babies or children born to women who are lacking iodine. It is a serious and nonreversible problem that should be avoided by proper iodine intake.
Iodine itself is a poisonous gas, as are the related halogens chlorine, fluorine, and bromine. However, as with chlorine, the salts or negatively charged ions of iodine (iodides) are soluble in water, and iodine is essential to life in trace amounts. Plants do not need iodine, but humans require it for the production of thyroid hormones that regulate the metabolic energy of the body and set the basal metabolic rate (BMR).
The body contains about 25 mg. of iodine. A small percentage of this is in the muscles,
20 percent is in the thyroid, and the rest is in the skin and bones. Only 1 percent is present in the blood. The concentration of iodine in the thyroid gland is very high, more than 1,000 times that in the muscles. Approximately one-fourth of thyroid iodine is in the two main thyroid hormones, T4 (thyroxine) and T3 (triiodothyronine). Thyroxine itself is nearly two-thirds iodine. The remainder is in the precursor molecules of these two important hormones.
Iodine is well absorbed from the stomach into the blood. About 30 percent goes to the thyroid gland, depending on the need. Iodine is eliminated rapidly. Most of the remaining 70 percent is filtered by the kidneys into the urine. Our bodies do not conserve iodine as they do iron, and we must obtain it regularly from the diet. There is recent concern that perhaps iodine is being overconsumed, especially in iodized salt. The incidence of goiter has been rising again, however, so there may be factors other than iodine involved in this problem.
Sources: The life from ocean waters provides the best source of iodine. Fish, shellfish, and sea vegetables (seaweed) are dependably rich sources. Cod, sea bass, haddock, and perch are a few examples of iodine-rich sea animals consumed by humans; kelp is the most common, high-iodine sea vegetable. Kelp in particular is rich in other minerals and low in sodium and thus is a good seasoning substitute for salt.
The use of iodized salt has certainly reduced most iodine deficiency. It contains about 76 mcg. of iodine per gram of salt. The average person consumes at least 3 grams of salt daily, exceeding the RDA for iodine of 150 mcg. Many authorities feel (and I believe) that commercial iodized salt is overused and has other drawbacks. It contains aluminum and other unneeded chemicals and may contribute to other problems. Fast foods may be very high in iodine because of the added salt. Adding iodine to salt is part of the paternalistic thinking of the industrial age, not counting on people to learn or adapt, “just put it in their food or water and save them from their own ignorance.” There are healthier ways to obtain iodine than in table salt; eating fish, especially fresh ocean fish, is probably the best, as it also may help reduce cholesterol and cardiovascular disease risk. Sea salt from the ocean water is a natural source of iodine, although it is not nearly as high in this mineral as “iodized” salt.
Dietary iodine content may vary widely, depending on the iodine content in the soil in which food grows. Plants grown in or animals grazed on iodine-rich soil will contain substantial amounts of iodine. Milk and its products may be sources of iodine when the cows have an iodized salt lick in their pasture. Eggs may also be a good source when iodine is in the chicken feed. Bakers may add iodine to dough, so some may be present in bread. Other foods that may contain iodine, especially when the soil is good, are onions, mushrooms, lettuce, spinach, green peppers, pineapple, peanuts, cheddar cheese, and whole wheat bread. More and more, people are eating wholesome, natural foods, avoiding iodized salt, so they must eat more of the iodine-rich foods, such as the sea vegetables, or obtain iodine from a general vitamin-mineral supplement to make sure they are getting adequate amounts.
Functions: Iodine is an essential nutrient for production of the body’s thyroid hormones and therefore is required for normal thyroid function. The thyroid hormones, particularly thyroxine, which is 65 percent iodine, are responsible for our basal metabolic rate (BMR)-that is, the body’s use of energy. Thyroid is required for cell respiration and the production of energy as ATP and further increases oxygen consumption and general metabolism.
The thyroid hormones, thyroxine and triiodothyronine, are also needed for normal growth and development, protein synthesis, and energy metabolism. As thyroid stimulates the energy production of the cellular mitochondria and affects our BMR, it literally influences all body functions. Nerve and bone formation, reproduction, the condition of the skin, hair, nails, and teeth, and our speech and mental state are all influenced by thyroid as well. Thyroid and, thus, iodine also affect the conversion of carotene to vitamin A and of ribonucleic acids to protein; cholesterol synthesis; and carbohydrate absorption.
Iodine is picked up by the thyroid and combines with the thyroid hormones and amino acid tyrosine to make the thyroid hormone precursors diiodotyrosine, diiodothyronine, and monoiodotyrosine and, then, the hormones T3 and T4. These hormones are then carried through the body by a protein called thyroid binding globulin (TBG).
Uses: Supplemental iodine may be helpful in correcting hypothyroidism and goiter caused by deficient iodine intake, and it may reverse many of the symptoms of cretinism if given soon after birth. Thus, iodine’s main use is really in the prevention or early treatment of its deficiency diseases.
Iodine has also been used to help increase energy level and utilization in cases of fatigue, mental sluggishness, and weight gain caused by hypothyroidism. Iodine itself will not help with weight loss if there is normal thyroid function. If weight gain results from iodine deficiency causing decreased thyroid activity, this hypothyroid condition may be improved with iodine followed by thyroid supplementation.
Iodine solutions, such as iodine tincture or Betadine, are commonly used as antiseptics and can actually kill bacteria and fungi.
Because of the thyroid’s role in fat and cholesterol metabolism, sufficient iodine and thus normal thyroid levels are thought to help reduce atherosclerosis potential. Also, iodine and thyroid may help maintain healthy hair, skin, and nails. It is possible that iodine deficiency increases the risk of certain cancers, such as breast, ovary, and uterus. Iodine levels may be low in people with fibrocystic breast disease; in this case, supplementation may improve this condition.
Potassium iodide has been used medicinally for problems of the skin and as an expectorant for bronchial congestion. Silver iodide has been used to seed clouds to bring rain, but this practice is considered ecologically unsound. Iodine supplements may help prevent uptake of radioactive iodine if that is present in the environment or in medical diagnostic procedures. If the thyroid were saturated with normal iodine, it would eliminate the radioactive molecules more rapidly.
Deficiency and toxicity: There is no significant danger of toxicity of iodine from a natural diet, though some care must be taken when supplementing iodine or using it in drug therapy. High iodine intake, however, may actually reduce thyroxine production and thyroid function. Excessive quantities of iodized salt, taking too many kelp tablets, or overuse of potassium iodide expectorants such as SSKI can cause some problems, but regular elevated intake of iodine is needed to produce toxicity. Some people have allergic reactions, mainly as skin rashes, to iodine products. Iodine supplementation may also worsen acne in some cases.
Deficiencies of iodine have been very common, especially in areas where the soil is depleted, as discussed earlier. Several months of iodine deficiency can lead to goiter and/or hypothyroidism. With decreased iodine, the thyroid cells and gland enlarge, creating a goiter, which may be noticed mainly by the swelling it causes in the base of the neck.
Goiter is usually associated with hypothyroidism, which is decreased thyroid function that leads to slower metabolism, fatigue, weight gain, sluggishness, dry hair, thick skin, poor mental functioning, decreased resistance to infection, a feeling of coldness, and a decrease in sexual energy. More advanced hypothyroidism may worsen these symptoms as well as create a hyperactive, manic state and hypertension, which is paradoxical because this may occur with an overactive thyroid as well. Iodine by itself usually will not cure goiter and hypothyroidism but often will slow their progression.
Goitrogens are substances that can induce goiter, primarily by interfering with the formation and function of thyroglobulin. Some natural goitrogens are soybeans, cabbage, cauliflower, and peanuts, especially when they
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come from iodine-deficient soils. Millet has recently been described as having goitrogenic tendencies. Certain drugs, such as thiouracil and sulfonamides, also act as goitrogens.
Some early studies correlate low iodine levels with an increased risk of breast cancer. These low levels usually correlate with low selenium levels as well, more classically associated with cancer. A higher incidence of breast cancer has been shown to occur in the goiter belt, whereas areas with high soil levels of iodine and selenium show a lower incidence.
Requirements: The RDA for iodine in adults is 150 mcg. The amount necessary to prevent goiter is about 1 mcg./kg.-that is, about 50-75 mcg. for most adults. Average intake from diet ranges from 65 mcg. to about 650 mcg. Much of that may come from iodized salt, which is not highly recommended; however, it is very difficult to avoid salt completely in our culture because it is added to so many prepared foods and by restaurants and mothers everywhere. A 6-ounce portion of ocean fish contains about 500 mcg. of iodine, more than is contained in one teaspoon of salt but without the extra 2 grams of sodium. Ideally, we can meet our iodine requirements by eating seafood, seaweed, and vegetables grown in iodine-rich soil. A typical mineral or complete vitamin supplement will contain the RDA, 150 mcg., of iodine per day. More iodine is needed during pregnancy and lactation. People on low-salt diets may need supplemental iodine.