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Mineral Nutrient :: Iodine

Iodine

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Content Below: What is Iodine · Benefits · Deficiency Signs · Foods · Supplements · RDA · Toxicity



What is Iodine ?
Iodine was one of the first nutrients to be identified as an essential trace mineral.  It is needed in only very small amounts by the body.

The body normally contains about 20 to 30 mg of iodine, of which 70-80% is stored in the thyroid gland, located in the lower front part of the neck. Smaller quantities are found in the salivary glands, stomach lining, blood, and lactating mammary glands.


How Iodine Benefits Health
Iodine is critical to life.  This is because it is needed by the thyroid gland for production of the thyroid hormones thyroxine (T4) and triiodothyronine (T3).  It forms an essential component of the hormones.

These hormones are vital not only for cell metabolism and normal growth, but also play a part in bio-chemical processes in the body.  If there is not enough iodine, then not enough thyroid hormones are produced, leading to damaging effects on the body's health.

The main ways that iodine benefits the body are summarized here.

:: Iodine Benefits & Functions
1. essential for proper functioning of the thyroid gland
2. necessary component for the synthesis of thyroid hormones and to prevent goiter
3. needed in cell metabolism and to convert food to energy
4. helps to metabolize excess fat
5. may help prevent fibrocystic breast disease (painful swelling of the breast) by regulating the effect of estrogen
6. important in physical and mental development
7. improves mental alertness and cognitive function
8. prevents multiple miscarriages


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Iodine Deficiency Symptoms and Causes
The body cannot make iodine but gets it from the diet. This is determined by the amount of iodine in the food which in turn depends on the content of it in soil and water.  Places with iodine-poor soils and snow-fed water or heavy rainfall that lower the level of iodine in water supplies, tend towards a low-iodine diet and greater risk of deficiency.

Iodine deficiency symptoms are rare in industralized countries such as the United States and Canada, where cattle feed and table salt are iodized (with iodine added).  But many other parts of the world have a low iodine diet and iodine deficiency remains a significant problem globally.

Selenium deficiency may also worsen the effect of a low iodine diet.  In such cases, the use of iodized salt or iodine supplements might be helpful.

Iodine deficiency symptoms are more commonly seen in women, especially pregnant women or those over 50, and older children, than in men.

Goitre, characterized by enlargement of the thyroid gland, is often the first sign of iodine deficiency.  It results from over-stimulation of the gland as the body tries to produce thyroid hormones in the absence of iodine.

The other classic symptom of chronic iodine deficiency is hypothyroidism, where the thyroid gland does not produce enough thyroid hormones.  This leads to other problems.  Some can be serious, such as cretinism, a type of mental and physical retardation in children arising from severe iodine deficiency in pregnancy or infancy.  It may be possible to correct cretinism in its initial stages with iodine supplementation, if caught early enough.

There are certain food compounds known as goitrogens, that hinder the absorption and utilization of iodine by the thyroid gland.  Foods that have goitrogens include the cruciferous vegetables like broccoli, Brussel sprouts, cabbage, cauliflower, kale, mustard and turnip.  Also soy and soy products like tofu, and cassava root, millet, peanuts, peaches, and strawberries.

People at risk of deficiency should avoid eating a lot of these foods, or at least cook them.  (Cooking mitigates their goitrogenic ability.)

A number of iodine deficiency symptoms have been identified.

:: Iodine Deficiency Symptoms
1. goitre (goiter) characterized by an enlarged thyroid gland which may cause a choking feeling or difficulty with breathing and swallowing (nodules can also develop within a goitre)
2. hypothyroidism (under-production of thyroid hormones) which can lead to symptoms such as brittle dry hair, hair loss, brittle nails, coarse dry pale skin, anemia, intolerance to cold, fatigue or weakness, depression, irritability, poor memory, weight gain, muscle or joint pain, constipation, decreased libido, infertility, abnormal menstrual cycles or heavy periods, and in more severe cases, hoarseness, decreased sense of taste and smell, mental impairment, skin thickening, and puffy face, hands or feet
3. impaired immune system
4. hearing loss in children
5. severe deficiency during pregnancy, breastfeeding or infancy can lead to neuro-cognitive defects in the baby, and problems with growth, speech and hearing; a particularly severe form of it is cretinism, characterized by brain damage or major mental retardation, speech problems, hearing loss, apathy, spasticity, and stunted growth
6. even mild iodine deficiency during pregnancy can hamper the growth of the child's brain, and has been linked to low intelligence in children
7. congenital hypothyroidism is the most common preventable cause of mental retardation; the National Health and Medical Research Council therefore recommends a higher daily intake of iodine during pregnancy and breastfeeding

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Iodine Foods
The iodine content of most natural foods is typically quite low, but varies with the soil they are grown in, and the water and fertilizers used.  Apart from foods containing iodine, the richest source is actually iodized salt.

Foods high in iodine are · salt-water fish · seafood and shellfish · seaweed like dulse, bladderwrack, kelp, nori · iodized table salt.

Other foods containing iodine include · eggs · dairy products like cow's milk, cheese, yogurt · garlic · lima beans · mushrooms · sea salt (not high in iodine but provides other minerals as well) · sesame seeds · soybeans and soy products · strawberries · some vegetables like asparagus, spinach, summer squash, swiss chard, turnip greens.

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Iodine Supplements
Taking vitamins and minerals in their correct balance is vital to the proper functioning of all vitamins.  They work synergistically, which means that the effectiveness of any one nutrient requires, or is enhanced, sometimes dramatically, by the presence of certain other nutrients.

For this reason, if you are looking to take supplements for maintenance of optimal health, the recommended approach is to take a multi-vitamin that has the proper balance of all the necessary nutrients your body needs.

For a list of reputable top ranked vitamin and mineral supplements chosen in an independent supplement review, see Best Multivitamin Supplements. Many of these are manufactured to pharmaceutical or nutraceutical GMP compliance, which is the highest multivitamin standard possible.

Keep in mind, however, that while mineral supplements are useful to plug nutritional gaps that are almost inevitable in modern diets, and to ensure we get optimal doses of nutrients, they are no substitute for a good diet. Instead, use them to complement a healthy diet and lifestyle.


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Iodine RDA (Recommended Dietary Allowance)
The Food & Nutrition Board of the Institute of Medicine, National Academy of Sciences, in their 1997-2001 collaboration between the US and Canada, set the daily Adequate Intake (AI) of Iodine as follows.

Life Stage | Gender Iodine Dosage | Day
Infants 0-6 mths 110* µg
Infants 7-12 mths 130* µg
Children 1-3 yrs 90 µg
Children 4-8 yrs 90 µg
Girls 9-13 Yrs 120 µg
Boys 9-13 Yrs 120 µg
Females 14-18 Yrs 150 µg
Males 14-18 Yrs 150 µg
Females 19-50 Yrs 150 µg
Males 19-50 Yrs 150 µg
Females older than 50 Yrs 150 µg
Males older than 50 Yrs 150 µg
Pregnant Women 14-18 Yrs 220 µg
Pregnant Women 19-50 Yrs 220 µg
Lactating Mothers 14-18 Yrs 290 µg
Lactating Mothers 19-50 Yrs 290 µg

These dosages are the minimum required per day to ward off deficiency. In therapeutic use of this nutrient, dosage is increased as necessary for the ailment, keeping in mind Iodine toxicity levels.

Legend

1 µg = 1 mcg = 1 microgram = 1/1,000,000 of a gram
1 mg = 1 milligram = 1/1,000 of a gram

* Indicates AI figures based on Dietary Reference Intake (DRI) figures


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Iodine Overdose Symptoms, Toxicity Level & Side Effects
There is normally not enough iodine in food alone to cause toxicity.  People get at most 210 to 300µg (micrograms) of it per day from foods containing iodine.  Even levels slightly higher than that are generally well tolerated by the body.

However, large amounts can be toxic.  Children are especially vulnerable to harm from excessive iodine.  Excess can occur from eating too many foods high in iodine (like dulse and kelp), or from medication or supplementation.

Excessive iodine intake can lead to hyperthyroidism (over-active thyroid), which causes over-production of thyroid hormones.  This accelerates the body's metabolism and results in palpitations, anxiety, irritability, sweating, and weight loss.

Interestingly, under certain circumstances, very high intake of iodine can actually have the opposite effect of inhibiting the production of thyroid hormones. This can result in disorders normally associated with deficiency, like goiter and hypothyroidism.

Other symptoms of iodine toxicity include: metallic taste in the mouth, a painful mouth or throat, thirst, shortness of breath, vomiting, diarrhea, abdominal pain, fever, shock or seizures, stupor, delirium.  Doses in excess of 1g can cause burning in the mouth, weak heartbeat, and even coma.

Certain people, those with an autoimmune thyroid disease (such as Grave's disease or Hashimoto's disease) or who have ever had hyperthyroidism or an iodine deficiency, are more prone to toxicity from excessive iodine, and should be careful with their intake.

The Food and Nutrition Board of the Institute of Medicine has set Tolerable Upper Intake Levels (ULs) for iodine.  These are levels above which there is risk of toxicity, especially when taken over a long time.

Tolerable Upper Intake Levels (UL) for Iodine per Day
Age Male Female Pregnancy Lactation
0 to 12 months *ND *ND    
1 to 3 years 200 µg 200 µg    
4 to 8 years 300 µg 300 µg    
9 to 13 years 600 µg 600 µg    
14 to 18 years 900 µg 900 µg 900 µg 900 µg
19 years & above 1,100 µg 1,100 µg 1,100 µg 1,100 µg
*ND : Not determinable.  Intake should be from food/milk only.

The ULs do not apply to the therapeutic use of iodine for treatment, which should be under the supervision of a healthcare professional.


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References

1. Institute of Medicine, Food and Nutrition Board. Dietary reference intakes for vitamin A, vitamin K, arsenic, boron, chromium, copper, iodine, iron, manganese, molybdenum, nickel, silicon, vanadium, and zinc. Washington, DC: National Academy Press; 2001.

2. U.S. National Libary of Medicine [NLM] & National Institutes of Health [NIH]: MedlinePlus. NLM-NIH home page. <http://www.nlm.nih.gov/medlineplus>. Use the built-in search function to find specific data. Accessed 2009 March – June.

3. American Thyroid Association. Iodine Deficiency. <http://www.thyroid.org/patients/patient_brochures/iodine_deficiency.html>. Accessed 2009 Jul 18.

4. The George Mateljan Foundation: The world's healthiest foods [WHFoods]. WHFoods home page. <http://www.whfoods.com>. Accessed 2009 March – June.

5. Balch JF, Balch PA. Prescription for nutritional healing: A practical A-Z reference to drug-free remedies using vitamins, minerals, herbs & food supplements. Garden City Park, New York: Avery Publishing; 1990.

6. Ulene A. Dr. Art Ulene's complete guide to vitamins, minerals and herbs. New York, NY: Avery Publishing; 2000.

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