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What is iodine?

Iodine is a mineral that is an essential nutrient to human life and health.

The chemical symbol for iodine is I.

Iodine Function

It is a part of the thyroid hormones triiodothyronine (T3) and thyroxine (T4), which are important for organ development, growth, metabolism and reproduction.

How much iodine do you need?

The Recommended Dietary Allowance (RDA) for iodine for adults is 150 mcg/day, for pregnant women 220 and for breastfeeding women 290 mcg/day [1].

Chart 1. List of Foods High in Iodine

PLANT FOODS Iodine (mcg)
Seaweed (1 g) 16-3,000
Potato with skin, baked (1 medium) 60
Bred, white, enriched (2 slices, 50 g) 45
Navy beans (1/2 cup) 32
Macaroni, enriched (1 cup) 27
Corn, cream style (1/2 cup) 14
Cod (3 oz, 85 g) 100
Milk (1 cup, 237 mL) 55
Yogurt, plain (1 container, 170 mL) 55
Fish sticks (3 oz, 85 g) 55
Shrimps (3 oz, 85 g) 35
Turkey breast (3 oz, 85 g) 35
Cheese (2 oz, 57 g) 25
Egg (1 large, 50 g) 25
Tuna (3 oz, 85 g) 15
Salt (iodized) (1 gram) 20-77

Chart 1 sources: Linus Pauling Institute [1], NIH.gov – Office of Dietary Supplements [4]

Human breast milk iodine concentration depends on the maternal iodine intake and may range from 5 to 2,000 mcg iodine per liter [3]. Low breast milk iodine concentration can be quickly improved by iodine supplements taken by mother [3]. The Adequate Intake (AI) for iodine for 0-6 months old infants is 110 mcg/day and for 7-12 months old infants 130 mg/day [1].

Iodized Salt

In many iodine insufficient countries, iodine in the form of potassium iodide (KI) is added to salt (77 mcg of iodine/gram salt in the U.S.; 20-44 mcg in other countries). Sodium iodide (NaI), sodium iodate (NaIO3), potassium iodate (KIO3) or calcium iodate [Ca(IO3)2] can be also used for salt iodization.

Iodine Deficiency: Causes, Symptoms

Iodine deficiency is usually caused by low iodine intake, mostly in areas with low amount of iodine in soil and no iodine added to salt [1]. Countries with moderate risk of iodine deficiency include Afghanistan, Algeria, Belarus, Central Africa, Dominican Republic, Fiji, Gambia, Kyrgyzstan, Senegal and Vietnam [5]. Rarely, and only in susceptible individuals, selenium, iron or vitamin A deficiency, or substances that lower iodine availability in the body (goitrogens) in cassava, soy, cabbage, cauliflower, broccoli or Brussels sprouts may cause iodine deficiency. Iodine deficiency results in decreased synthesis of thyroid hormones thyroxine (T4) and triiodothyronine (T3), followed by an increased secretion of thyroid stimulating hormone (TSH) from the pituitary gland, which results in enlarged thyroid gland (goiter).

Iodine deficiency in infants (or fetuses due to iodine deficiency in their mothers) may result in cretinism with impaired brain development and permanent mental retardation, short stature, deafness and other birth defects [1].

Low thyroid hormone levels (hypothyroidism) in older children and adults cause goiter, fatigue, impaired mental function, low body temperature with cold intolerance, weight gain and constipation. Pregnant women with iodine deficiency are at increased risk to have a miscarriage.

Enlarged thyroid gland may trap more radioactive iodine I133, released during nuclear accidents, thus increasing the risk of developing thyroid cancer [1].

Diagnosis of Iodine Deficiency

In iodine deficiency, blood tests show low T3 and T4 and high TSH levels, and urine tests show lowered iodine excretion [1].

Iodine Supplements

Supplements without prescription (over-the-counter):

  • Potassium iodide is included in certain multivitamin/mineral products.

Supplements by prescription:

  • Potassium iodide

Iodine Benefits

Iodine supplements are LIKELY EFFECTIVE for [1,2]:

  • Prevention or treatment of iodine deficiency
  • Lessening symptoms of fibrocystic breast disease
  • Potassium iodide taken within 48 hours before or 8 hours after the nuclear accident can significantly lower the uptake of radioactive iodine (I133) by the thyroid gland and thus decreases the risk of developing a thyroid gland cancer in the exposed individuals. Iodized salt does not seem to provide enough iodine to protect against (I133).

Iodine supplements are POSSIBLY EFFECTIVE for [2]:

  • Conjunctivitis (pink eye)
  • Breast pain (mastalgia) related to menstrual cycle

There is INSUFFICIENT EVIDENCE of iodine supplements in prevention or treatment of fungal skin condition (Cutaneous sporotrichosis) [2].

Iodine Safety: Side Effects, Toxicity

The Tolerable Upper Intake Level (UL)–the amount that should not cause any side effects–for iodine for adults is 1,100 mcg (1,1 mg) per day [1].

Possible side effects of iodine supplements include nausea, stomach pain, runny nose, headache, metallic taste and diarrhea, worsening of dermatitis herpetiformis [2]. In sensitive people, iodine can cause swelling of the lips and face (angioedema), bleeding, bruising, fever, joint pain, lymph node enlargement, allergic reactions including hives, or death.

Acute iodine poisoning occurs only when several grams of iodine (amount not likely present in food or supplements) are consumed. Symptoms include burning mouth and stomach, fever, diarrhea and, in severe cases, coma [1].

Chronic iodine toxicity. Excessive iodine intake (more than 18,000 mcg/day) may, in long-term, result in hypothyroidism, hyperthyroidism, autoimmune thyroid disease, thyroid papillary cancer, or iodermia (severe skin reaction).

In individuals with iodine deficiency with goiter or cystic fibrosis (but not likely in healthy people), iodine doses as small as 150 micrograms/day may trigger iodine induced hyperthyroidism (IIH) [1].

“Iodine Allergy”

Allergy to iodine or potassium iodide used in supplements probably does not exist. People often have various reactions to iodine-containing contrast dyes used in radiology or in household cleansers, but these are not iodine allergies. In seafood allergies, sensitive people react to proteins in seafood flesh, not to iodine.

Iodine Interactions With Drugs

Drugs that may increase blood iodine levels if taken together with iodine supplements: amiodarone, ACE inhibitors (such as captopril, enalapril), angiotensin receptor blockers, such as losartan and valsartan, or diuretics, such as spironolactone and triamterene [2].

Iodine containing anti-arrhythmic medication amiodarone and a red coloring agent erythrosine (E127) added to certain foods and medications, may disrupt thyroid function [1].

Iodine supplements may increase the effect of medications for overactive thyroid, such as methenamine mandelate or methimazole [2].

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