Iodine

Iodine is an essential mineral — meaning your body cannot make it and must obtain it from food or supplements. Once absorbed in the small intestine, iodine travels through the bloodstream to the thyroid gland, where it is used to produce the hormones thyroxine (T4) and triiodothyronine (T3). These hormones play a central role in regulating energy production, temperature control, protein synthesis, and overall metabolic rate.

The thyroid gland acts as the body’s iodine reservoir, storing enough iodine to sustain hormone production for several weeks. When your body needs more energy or cellular repair, the brain (via the pituitary gland) releases thyroid-stimulating hormone (TSH), signalling the thyroid to release T4 and T3 into the bloodstream.

Iodine’s role extends beyond thyroid health — it supports normal growth and brain development, particularly during pregnancy and early childhood. It also assists with detoxification processes and the maintenance of healthy skin and cognitive function.

Since the body can’t synthesise iodine, dietary intake is key. Major sources include iodised salt, seafood (especially seaweed, cod, and shrimp), dairy products, and eggs. However, both too little and too much iodine can disrupt thyroid function. The body maintains a narrow optimal range — enough to support hormone production but not so high that it triggers inflammation or hormone imbalance.

Iodine directly influences how efficiently your body burns energy, repairs tissue, and maintains temperature balance. It is essential for thyroid hormone synthesis, making it one of the most important nutrients for metabolic and endocrine health.

Deficiency:
When iodine intake is too low, the thyroid gland cannot produce sufficient T4 and T3. This leads to hypothyroidism, where metabolism slows down. Common symptoms include fatigue, weight gain, hair loss, cold intolerance, dry skin, and low mood. Over time, the thyroid enlarges in an attempt to capture more iodine from the bloodstream — forming a goitre (swollen thyroid).

Severe iodine deficiency during pregnancy can cause developmental delays and cognitive impairment in children. Even mild deficiency in adults can affect concentration, energy, and overall vitality.

Excess:
Too much iodine can also disrupt thyroid function. Chronic high intake can overstimulate thyroid hormone production, leading to hyperthyroidism, characterised by rapid heart rate, anxiety, weight loss, and sleep disturbances. It can also trigger autoimmune thyroid disorders, such as Hashimoto’s thyroiditis (autoimmune hypothyroidism) and Graves’ disease (autoimmune hyperthyroidism), in genetically susceptible individuals.

Iodine balance and disease risk:
Iodine deficiency remains one of the most common micronutrient deficiencies globally, especially in populations that consume little seafood or non-iodised salt. Conversely, in countries with widespread salt iodisation or high seaweed consumption, excess iodine exposure is becoming more common.

Maintaining optimal iodine levels supports metabolic efficiency, hormonal balance, cognitive performance, and fertility. Balanced iodine intake is particularly critical for women of reproductive age, pregnant women, and individuals with thyroid disease, as they are most sensitive to iodine fluctuations.

Dietary Factors:

• Low iodine intake: Insufficient dietary iodine from limited seafood, eggs, or iodised salt can lead to deficiency.

• High iodine intake: Overconsumption of iodine-rich foods such as seaweed (kelp, nori, wakame), excessive use of iodised salt, or iodine-containing supplements can cause elevated levels.

• Goitrogens: Certain foods — particularly raw cruciferous vegetables (broccoli, kale, cabbage) and soy — contain compounds that can reduce iodine uptake by the thyroid when eaten in very large amounts. Cooking these foods generally neutralises this effect.
  

Lifestyle Factors:
Smoking and chronic alcohol consumption can impair iodine absorption and thyroid hormone metabolism. Certain medications, such as amiodarone (a heart medication) and anti-septics containing iodine, can alter iodine levels or mimic iodine toxicity.

Related Biomarkers:

• TSH, Free T4, and Free T3: Reflect thyroid hormone synthesis and metabolism.

• Thyroid antibodies (TPOAb, TgAb): Indicate autoimmune thyroid activity, often triggered by excessive iodine intake.

• Selenium: Supports the conversion of T4 to T3; low selenium can worsen the effects of iodine imbalance.
  

Micronutrient Impacts:

• Selenium and Iron: Work synergistically with iodine for thyroid hormone synthesis and conversion.

• Vitamin A and Zinc: Support thyroid hormone receptor activity and regulation. Deficiencies can magnify iodine-related dysfunction.
  

Environmental Influences:
Soil iodine content varies geographically — areas with iodine-depleted soil (e.g., mountainous regions) produce crops with low iodine content, leading to regional deficiencies. Conversely, exposure to iodine-rich disinfectants or sea spray can increase iodine levels.

If Your Results Are High

Excess iodine can overstimulate the thyroid and trigger hyperthyroidism or autoimmune thyroiditis.

Diet:

• Limit iodine-rich foods such as seaweed, iodised salt, shellfish, and dairy until levels normalize.

• Avoid processed foods fortified with iodine.
  .

Lifestyle:

• Avoid iodine-containing supplements, anti-septics, or medications unless prescribed.

• Maintain hydration to assist kidney excretion of excess iodine.
  .

Supplements:

• Discontinue any iodine or kelp-based supplements.

• Support thyroid balance with selenium-rich foods (e.g., Brazil nuts, tuna, eggs) under supervision.
  
  Additional Tests to Consider: Thyroid antibody panel (TPOAb, TgAb) to rule out autoimmune activation.

If Your Results Are Low

Low iodine can impair thyroid hormone production and slow metabolism.

Diet: Include natural iodine sources such as iodised salt, seafood (cod, shrimp), dairy, eggs, and seaweed in moderation.

Lifestyle:

• Ensure adequate caloric and protein intake, as malnutrition can reduce iodine absorption.

• Avoid chronic consumption of raw cruciferous vegetables in very high amounts.
  .

Supplements: Consider an iodine supplement or multivitamin containing iodine under medical supervision, especially if pregnant, breastfeeding, or vegan.

1. Rohner F, Zimmermann M, Jooste P, et al. Biomarkers of Nutrition for Development— Iodine Review. The Journal of Nutrition. 2014;144(8):1322S–1342S. doi:10.3945/jn.113.181974
   

2. Opazo MC, Coronado-Arrázola I, Vallejos OP, et al. The Impact of the Micronutrient Iodine in Health and Diseases. Critical Reviews in Food Science and Nutrition. 2022;62(6):1466–1479. doi:10.1080/10408398.2020.1843398
   

3. Lisco G, De Tullio A, Triggiani D, et al. Iodine Deficiency and Iodine Prophylaxis: An Overview and Update. Nutrients. 2023;15(4):1004. doi:10.3390/nu15041004
   

4. Zimmermann MB, Boelaert K. Iodine Deficiency and Thyroid Disorders. The Lancet Diabetes & Endocrinology. 2015;3(4):286–295. doi:10.1016/S2213-8587(14)70225-6
   

5. Caldwell KL, Pan Y, Mortensen ME, et al. Iodine Status in the United States Population, National Health and Nutrition Examination Survey 2011–2014.Thyroid. 2017;27(9):1179–1187. doi:10.1089/thy.2016.0652