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Iodine is an essential micronutrient present in very small amounts in our body. Iodine enters into the composition of the thyroid hormones produced by the thyroid gland. In fetuses and small children, thyroid hormones regulate the growth and development of most organs, especially the brain and cell differentiation. In people of all ages, they also stimulate metabolism and oxygen consumption by tissues. 

Roles

What does iodine do? 

  • Produces thyroid hormones (T3 and T4);
  • Regulates the metabolism of carbohydrates, lipids, and proteins;
  • Develops the nervous system;
  • Promotes normal heart function;
  • Promotes muscle development and function;
  • Promotes skeletal growth and maturation;
  • Stimulates lactation in breastfeeding mothers;
  • Promotes the health of skin, hair, nails, etc.;
  • Promotes gastrointestinal mobility;
  • Regulates basal metabolism: the energy expended at rest (lying down) while awake in a neutral temperature environment.

Used externally, iodine has antiseptic and disinfecting properties and serves as a contrast material in radiology exams.

Needs

A normal diet generally provides all the iodine people need. The body gets the iodine it requires in the form of mineral salts called iodides, and iodide requirements depend on the accumulation and replenishment of iodine in the thyroid gland. 

Recommended Dietary Allowance (RDA) for Iodine: 

Age
Amount (µg/Day) (RDA)
Infants
Birth to 6 months
110 (AI*)
7 to 12 months
130 (AI*)
Children
1 to 3 years
90
4 to 8 years
90
Preteens
9 to 13 years
120
Teens
Age 14 and older
150
Pregnant women
 
220
Nursing women

290

Source: DRI, Dietary Reference Intakes, 2006, p.320.

*(AI) = Adequate intake for those two age groups.

Sources

Most foods contain a small amount of iodine that varies with the iodine content of the soil they were harvested from and the type of irrigation and fertilizers used. Most foods have an iodine content of 3 to 75µg of iodine per portion. Some processed foods contain large amounts of iodine from the addition of iodized salt or additives, such as calcium or potassium iodate and potassium or copper iodide. 

Note: The addition of iodine to table salt is mandatory in Canada. 76 mg of potassium iodide per kilogram of salt is used. Sea salt does not have to be iodine enriched. Make sure the sea salt you choose is. 

 Food Sources for Iodine: 

Foods
Portion size
(Iodine = µg)
Seafood (including seaweed)
 
 
Iodized table salt
1 tsp
134
Dairy products, 2%
250ml
56
Cooked cod
85mg
99
Whole grain bread
2 slices
32
Cooked cornmeal
250ml
68
Cooked shrimp
85mg
35
1 large cooked egg
 
24

Source: DRI, Extenso.

Deficiency

Iodine deficiency is rare in North America because iodized salt is the most common source of iodine consumption. The most serious repercussion of iodine deficiency is the effect on the developing brain. To make thyroid hormones, the thyroid gland needs two other trace elements besides iodine: zinc and selenium. If an body is deficient in any of these three trace elements, thyroid function may slow. 

Signs of iodine deficiency: 

  • Goiter (enlargement of the thyroid gland);
  • Mental delay;
  • Hypothyroidism;
  • Cretinism (neurological problems caused by hypothyroidism in the fetus);
  • Growth and development disorders.

Indications

In healthy individuals, the amount of iodine needed for the body to function properly varies by diet, age, physiological state, physical activity, and medications taken. 

The following groups should monitor their iodine intake: 

  • Pregnant and nursing women;
  • Menopausal women (hormonal changes);
  • Athletes (during heavy sweating);
  • Infantss;
  • Adolescents (hormonal changes);
  • Older adults;
  • People who live far from the sea;
  • People on a salt-free diet;
  • Vegetarians;
  • Smokers (tobacco interferes with the body’s iodine absorption);
  • People who eat large amounts of radishes, cabbage, and broccoli (goitergenic vegetables);
  • People taking certain medications (see list in the interactions section).

Note: In industrialized countries, the blood TSH level of all newborns is checked at the hospital to determine whether or not they suffer from congenital hypothyroidism. 

Adverse effects

A large amount of iodine from foods is well tolerated by most people. 

Signs of excess iodine: 

  • Thyroiditis;
  • Goiter;
  • Hypothyroidism;
  • Hyperthyroidism;
  • Hypersensitivity reactions;
  • Metallic taste;
  • Gum and tooth pain;
  • Thyroid cancer;
  • Symptoms of acute iodine poisoning;
    • Burning feeling in the mouth, throat, and stomach;
    • Abdominal pain;
    • Fever;
    • Nausea, vomiting, diarrhea.

Cons-indications

As a supplement

  • People with auto-immune thyroid diseases;
  • People with iodine deficiencies.

Note: People can be allergic to iodine-containing products but not to the iodine itself. All products capable of triggering an immune response contain iodine, but the induced immunological response is caused by the other molecules, not the trace element. 

Interactions

Natural health products and vitamin supplements: 

  • A number of natural health products to treat the thyroid are rich in iodine, including iodine tincture, seaweed-based iodized supplements, and others;
  • Cruciferous vegetables such as cabbage, turnips, rutabagas, broccoli, radishes, and mustard greens, as well as manioc, millet, peanuts, and soybean seeds contain so-called goitergenic substances that block iodine and prevent its use. Eating large amounts of these raw foods can cause problems; cooking negates their goitergenic effects;
  • Fucus vesiculosis thalle (kelp, a seaweed very rich in iodine).

Drugs: 

  • Drugs for hypothyroidism: their use in conjunction with iodine can cause hyperthyroidism;
  • Lithium: can increase the hypothyroidism effect;
  • Anti-arrhythmia medications (can cause hypothyroidism or hyperthyroidism).

Additional information

Speak with your pharmacist if you plan to take iodine supplements. Your pharmacist can help you choose the solution that’s best for you based on your health and any drugs you take.

Other names

Iode, Iodine, I