Iodine

• Thyroid Function
• Metabolic Regulation
• Cognitive Development

• Immune Function
• Breast Health
• Fetal Development
• Detoxification
• Antioxidant Activity

Iodine is an essential trace element that serves as a critical component of the thyroid hormones thyroxine (T4) and triiodothyronine (T3). These hormones regulate metabolic processes throughout the body and are vital for normal growth and development, particularly of the brain and nervous system. When ingested, iodine is rapidly absorbed in the stomach and small intestine, primarily as iodide. The thyroid gland actively concentrates iodide from the bloodstream via the sodium-iodide symporter (NIS), concentrating it 20-40 times higher than plasma levels.

Within the thyroid follicular cells, iodide is oxidized to iodine by thyroid peroxidase (TPO) and incorporated into tyrosine residues on thyroglobulin to form monoiodotyrosine (MIT) and diiodotyrosine (DIT). These iodinated tyrosines couple to form T3 (one MIT + one DIT) and T4 (two DIT molecules). The thyroid hormones are then stored within the thyroid follicle’s colloid until needed, at which point they are released into the bloodstream to regulate metabolism throughout the body. T3, the more active form, primarily forms in peripheral tissues through the deiodination of T4.

Beyond its role in thyroid hormone production, iodine also functions as an antioxidant, particularly in breast tissue and the gastric mucosa, and may have antimicrobial properties. In the immune system, iodine is used by leukocytes in the iodination reaction during the respiratory burst to kill bacteria.

The Recommended Dietary Allowance (RDA) for iodine is 150 micrograms (mcg) per day for most adults. Higher amounts are recommended during pregnancy (220 mcg) and lactation (290 mcg) to support fetal and infant development. The Tolerable Upper Intake Level (UL) is set at 1,100 mcg per day for adults, as excessive iodine can disrupt thyroid function.

Iodine is rapidly and efficiently absorbed in the stomach and small intestine, with approximately 90% of ingested iodine (as iodide) being absorbed under normal conditions. Absorption occurs primarily in the small intestine through sodium-iodide symporters. Once absorbed, iodine circulates in the bloodstream, where it’s primarily taken up by the thyroid gland (about 30% of circulating iodide under normal conditions) or excreted by the kidneys (>90% of what’s not taken up by the thyroid).

Consuming iodine in the form of potassium iodide or sodium iodide (highly bioavailable forms), Ensuring adequate selenium status, as selenium is required for thyroid hormone metabolism, Avoiding excessive consumption of goitrogens (compounds that interfere with iodine uptake) found in raw cruciferous vegetables, soy, and certain other foods, Correcting iron deficiency, which can impair thyroid peroxidase activity, Avoiding excessive calcium intake at the same time as iodine supplements, as calcium may slightly reduce iodine absorption

Iodine supplements can be taken at any time of day, with or without food.

However , for individuals taking levothyroxine (synthetic thyroid hormone), iodine supplements should be taken at least 4 hours apart from thyroid medication to avoid potential interference with absorption. For those concerned about goitrogens in the diet, taking iodine supplements at a different time than consuming goitrogen-rich foods may be beneficial,

although cooking largely inactivates most goitrogens.

When using iodine for radiation protection, timing is critical – potassium iodide should be taken just before or immediately after radiation exposure for maximum effectiveness.

• Metallic taste
• Mouth and throat irritation (with some forms)
• Stomach upset
• Diarrhea
• Nausea
• Headache
• Rash
• Allergic reactions (rare)
• Thyroid dysfunction (with excessive intake)
• Iodism (iodine toxicity) with high doses: salivation, sneezing, headache, fever

• Hypersensitivity to iodine
• Dermatitis herpetiformis
• Thyroid disorders (including Graves’ disease, Hashimoto’s thyroiditis, thyroid nodules, or thyroid cancer) unless under medical supervision
• Hyperkalemia (when using potassium iodide)
• Tuberculosis (high-dose iodine may exacerbate)
• Kidney disease (when using potassium iodide)
• Myotonia congenita
• Hypocomplementemic vasculitis

• Lithium (increased risk of hypothyroidism)
• Antithyroid medications (potentiated effect)
• ACE inhibitors (increased risk of hyperkalemia with potassium iodide)
• Potassium-sparing diuretics (increased risk of hyperkalemia with potassium iodide)
• Amiodarone (contains iodine; additive effects)
• Warfarin (potential altered effectiveness)
• Thyroid hormones (potential interference with treatment)

The Tolerable Upper Intake Level (UL) for iodine is 1,100 mcg (1.1 mg) per day for adults. This limit is based on the potential for higher amounts to cause thyroid dysfunction. Some individuals, particularly those with underlying thyroid conditions or those living in areas with historically low iodine intake, may be sensitive to iodine intakes even below this level. Conversely, certain populations with historically high iodine intake (such as some Japanese populations consuming large amounts of seaweed) may tolerate higher levels without adverse effects.

Acute toxicity is rare but can occur with very high doses (several grams), while chronic excess intake is more commonly associated with thyroid dysfunction, including both hypothyroidism and hyperthyroidism.

Iodine is recognized as Generally Recognized as Safe (GRAS) by the FDA when used as a nutrient supplement within established limits. Potassium iodide (KI) is FDA-approved as an over-the-counter drug for thyroid blocking in radiation emergencies. The FDA has established a Reference Daily Intake (RDI) of 150 mcg for iodine, which is used for nutrition labeling purposes. The FDA requires that products labeled as ‘iodized salt’ contain 45-80 mg of iodine per kg of salt.

Eu: Regulated as a food supplement under Directive 2002/46/EC. The European Food Safety Authority (EFSA) has established a Population Reference Intake (PRI) of 150 mcg/day for adults. Iodization of salt is mandatory in some European countries and voluntary in others.

Canada: Regulated by Health Canada as a Natural Health Product (NHP) ingredient. The recommended daily allowance is 150 mcg for adults. Iodization of salt is mandatory for table salt and salt used in processed foods, with some exceptions.

Australia: Regulated by the Therapeutic Goods Administration (TGA) as a listed medicine ingredient. Mandatory fortification of bread with iodized salt was implemented in 2009 to address iodine deficiency.

Who: The World Health Organization recommends universal salt iodization (USI) as the main strategy for eliminating iodine deficiency disorders globally. WHO defines optimal iodine nutrition as a population median urinary iodine concentration of 100-199 mcg/L.

Low

$0.01-$0.10 per day for iodized salt or basic supplements; $0.10-$0.50 per day for specialty forms like nascent iodine or kelp supplements

Iodized salt provides the most cost-effective source of iodine, costing pennies per day for adequate intake. Standard multivitamin/mineral supplements containing iodine are also economical, typically providing 150 mcg of iodine as part of a comprehensive formula. Potassium iodide supplements are moderately priced and provide a reliable, standardized dose. Kelp and seaweed supplements vary widely in price and iodine content, making their value proposition less consistent.

Specialty forms like nascent iodine or liposomal iodine command premium prices but have limited evidence for superior bioavailability or efficacy compared to standard forms. For most individuals without specific absorption issues, basic iodine supplements or iodized salt provide excellent value. In regions with endemic iodine deficiency, iodized salt represents one of the most cost-effective public health interventions available, with benefit-to-cost ratios estimated at 30:1 or higher. For pregnant women, prenatal vitamins containing iodine offer good value given the critical importance of iodine during pregnancy and the relatively low incremental cost.

Potassium iodide tablets typically have a shelf life of 5-7 years when properly stored. Liquid iodine solutions like Lugol’s have a shorter shelf life of approximately 1-2 years once opened. Kelp and seaweed supplements generally have a shelf life of 2-3 years.

Store iodine supplements in a cool, dry place away from direct light. Liquid iodine preparations should be kept in dark, airtight bottles to prevent degradation and evaporation. Potassium iodide tablets for radiation emergencies should be stored according to specific guidelines from health authorities, typically in original packaging at room temperature. Iodized salt should be kept in a sealed container to prevent moisture absorption, which can cause iodine loss.

Exposure to light (especially for liquid iodine solutions), Heat (accelerates volatilization and degradation), Moisture (can cause degradation of tablets and loss of iodine from salt), Air exposure (iodine can sublimate), Acidic or alkaline conditions (can affect stability), Reducing agents (can convert iodine to iodide), Metal ions (can catalyze oxidation reactions)

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• Urinary iodine concentration (UIC) – measures recent iodine intake; population median of 100-199 mcg/L indicates adequate intake
• 24-hour urinary iodine excretion – more accurate than spot UIC but more difficult to collect
• Thyroid-stimulating hormone (TSH) – elevated in iodine deficiency; normal range typically 0.4-4.0 mIU/L
• Serum thyroxine (T4) and triiodothyronine (T3) – decreased in iodine deficiency
• Thyroglobulin – elevated in iodine deficiency; useful population biomarker
• Thyroid volume by ultrasound – increased in chronic iodine deficiency (goiter)
• Iodine loading test – measures urinary excretion after an oral iodine load; controversial method
• Iodine patch test – topical application with observation of absorption rate; not scientifically validated
• Hair iodine analysis – not widely accepted as reliable

Synthesis Methods

Natural Sources

Quality Considerations

Iodine has a rich history in medicine and public health dating back to ancient times. The use of seaweed and burnt sponge (rich in iodine) to treat goiter was documented in Chinese medical texts from 3600 BCE and later by Hippocrates in ancient Greece. However, the element itself wasn’t discovered until 1811 by French chemist Bernard Courtois, who isolated it from seaweed ash. In 1820, Swiss physician Jean-François Coindet first used iodine tincture to successfully treat goiter, establishing its medical importance.

The connection between iodine deficiency and endemic goiter was firmly established in the early 1900s, leading to the first public health intervention with iodized salt in Switzerland in 1922. The United States began iodizing salt in 1924, dramatically reducing the prevalence of goiter in previously endemic areas like the ‘goiter belt’ around the Great Lakes. In the 1960s, researchers recognized that iodine deficiency caused not only goiter but also cretinism (severe intellectual disability) and other developmental abnormalities, collectively termed ‘iodine deficiency disorders’ (IDD). This understanding led to global iodization programs coordinated by the WHO and UNICEF starting in the 1990s, one of the most successful public health interventions in history.

Beyond thyroid health, iodine has been used as an antiseptic since the 1800s, with iodine tincture and Lugol’s solution becoming standard for wound disinfection. During the Cold War, potassium iodide was stockpiled as a protective measure against nuclear radiation, blocking radioactive iodine uptake by the thyroid. Today, while severe iodine deficiency has been largely eliminated in many countries, mild to moderate deficiency remains a concern in specific populations, including pregnant women and those following restricted diets.

Iodine supplementation during pregnancy and effects on child neurodevelopment in areas of mild-to-moderate iodine deficiency, Impact of iodine supplementation on thyroid function in euthyroid adults with iodine deficiency, Effects of different doses of iodine supplementation on thyroid function in regions with varying baseline iodine status, Iodine supplementation and cognitive function in school-age children, Maternal iodine status and infant outcomes in areas of iodine sufficiency