Iodine

Quick summary

Iodine is an essential mineral important for the synthesis of thyroid hormones, which regulate metabolism, growth, and development across the lifespan.

What is it?

Iodine is a trace mineral that the body requires in small amounts to maintain normal physiological function. It is primarily known for its critical role in thyroid hormone production. These hormones are vital regulators of numerous metabolic processes as well as growth and neurological development, particularly during fetal development and early childhood.

Main functions in the body

• Synthesis of thyroid hormones (thyroxine (T4) and triiodothyronine (T3))
• Regulation of metabolic rate and energy production
• Support of normal growth and neurological development, especially during fetal and early childhood stages

Recommended intake and upper limit

Recommended Dietary Allowance (RDA) or Adequate Intake (AI) for iodine varies by age, sex, and life stage, including pregnancy and lactation. Authoritative sources such as the NIH Office of Dietary Supplements provide detailed guidelines. Likewise, Tolerable Upper Intake Levels (UL) exist to avoid excess iodine intake that could disrupt thyroid function.

Because recommended values differ widely based on individual factors, those interested should consult reliable sources or healthcare professionals for precise guidance tailored to their circumstances.

Best food sources

• Seafood (e.g., fish, shellfish, seaweed)
• Dairy products
• Iodized salt
• Eggs
• Some grains and vegetables, depending on the iodine content of the soil where they are grown

Deficiency: causes, symptoms and risk groups

Iodine deficiency remains a significant public health concern in some regions, particularly where iodine-poor soils limit natural dietary intake.

• Risk groups include: Pregnant and lactating women, infants and young children, people living in areas with iodine-deficient soils or limited access to iodized salt, and individuals with restricted diets low in iodine-containing foods.
• Signs and symptoms: Enlarged thyroid gland (goiter), hypothyroid symptoms such as fatigue, weight gain, and cold intolerance, cognitive impairments and developmental delays in children, and in severe cases during pregnancy, increased risk of cretinism (a condition of severe intellectual disability and growth retardation).

Globally, iodine deficiency is recognized as a leading preventable cause of intellectual disability and impaired development, underscoring the importance of adequate iodine intake during pregnancy and early life.

Supplement forms

No detailed information on specific iodine supplement forms was provided in the supplied data. Common supplemental forms generally include potassium iodide and sodium iodide, but evidence comparing these or others was not included here.

Absorption and bioavailability

Iodine is well absorbed from the gastrointestinal tract, primarily in the form of iodide. However, the supplied data did not provide detailed insights into factors that may enhance or inhibit iodine absorption, nor did it describe differences between various supplemental forms regarding bioavailability.

Potential benefits: what does the evidence say?

Thyroid hormone production and prevention of iodine deficiency disorders

The evidence supporting iodine’s essential role in the synthesis of thyroid hormones and prevention of iodine deficiency disorders is strong and well established in human populations. Adequate iodine supply is critical for maintaining normal thyroid function and preventing disorders such as goiter and hypothyroidism.

However, clinical benefits of iodine supplementation beyond correcting deficiency states are not confirmed in the supplied data. Thus, supplementation in individuals without deficiency should be approached cautiously and under professional advice.

Side effects and toxicity

Excessive iodine intake may lead to thyroid dysfunction, including the development of hyperthyroidism (overactive thyroid) or hypothyroidism (underactive thyroid). Intakes exceeding the established Tolerable Upper Intake Level (UL) may increase the risk of such adverse effects.

Therefore, adherence to recommended intake limits is advisable to avoid potential thyroid-related complications.

Special considerations:

• Individuals with pre-existing thyroid disorders should monitor iodine intake carefully and consult healthcare professionals for personalized guidance.
• Pregnant and lactating women require balanced iodine intake to meet their increased needs without exceeding safety thresholds.

Drug and nutrient interactions

No specific data on iodine-drug or iodine-nutrient interactions were provided in the supplied information.

Who should be careful?

• Individuals with thyroid disorders, including autoimmune thyroid disease, should consult healthcare professionals about their iodine intake.
• Pregnant and breastfeeding women should seek professional advice to ensure adequate but safe iodine consumption.
• People with medical conditions, kidney disease, or iron overload disorders, or those taking medications affecting thyroid function or iodine metabolism, should discuss iodine intake with their healthcare provider.

Frequently asked questions

• Q: Why is iodine important during pregnancy?
  A: Iodine supports the production of thyroid hormones critical for fetal brain development and growth. Severe deficiency during pregnancy can cause serious developmental issues.
• Q: Can I get enough iodine from diet alone?
  A: In many regions, iodized salt and iodine-rich foods like seafood and dairy products provide sufficient iodine. However, dietary sufficiency depends on local iodine levels in food and soil.
• Q: Is taking iodine supplements safe for everyone?
  A: While supplements can help correct deficiency, excess intake may cause thyroid problems. Those without deficiency should avoid high-dose supplements unless advised by a healthcare professional.
• Q: What symptoms suggest iodine deficiency?
  A: Signs may include fatigue, enlarged thyroid gland (goiter), weight gain, cold intolerance, and in children, impaired cognitive development.

Evidence limitations

• Limited data supplied on supplement forms, absorption enhancers/inhibitors, and detailed dosing guidelines.
• No explicit EU-authorized health claims related to iodine were provided in the source data.
• Safety profile details and contraindications beyond general toxicity risks are not comprehensively addressed in the supplied information.

References

• NIH Office of Dietary Supplements: Iodine – Health Professional Fact Sheet

Disclaimer: This information is intended for educational purposes only and does not constitute medical advice. Consult a qualified healthcare professional before making changes to your diet, supplement routine, or if you have medical conditions.

Last reviewed

June 2024