iodine
Iodine is a trace element required to synthesize the thyroid hormones triiodothyronine (T3) and thyroxine (T4), which regulate metabolism and are critical for fetal neurodevelopment. It matters across nutrition, endocrinology, obstetrics, and public health because both deficiency and excess have measurable population-level effects. For content strategy, iodine sits at the intersection of micronutrient education, prenatal care, thyroid disease management, and fortification policy — making it a high-value topic for health, pregnancy, and public health audiences.
- Atomic number
- 53
- Atomic weight
- 126.90 g·mol−1
- Discovery
- Discovered by Bernard Courtois in 1811
- Global insufficiency
- Approximately 2 billion people worldwide have insufficient iodine intake (WHO estimate)
- Recommended daily intake (RDA)
- Adults 150 µg/day; Pregnant 220 µg/day; Lactating 290 µg/day (US Institute of Medicine/WHO aligned guidance)
- Tolerable upper intake level (UL)
- Adults UL 1,100 µg/day (Institute of Medicine)
- Public health milestone
- First large-scale iodized salt program introduced in 1924 (United States) to reduce goiter
Biological role and biochemical mechanisms
Thyroid hormones regulate basal metabolic rate, thermogenesis, cardiovascular function, and — crucially during pregnancy and early life — neuronal migration, myelination, and synaptogenesis. Because the fetal thyroid is immature until mid-gestation, maternal iodine status and hormone supply have outsized effects on fetal brain development.
At the cellular level, iodine also exhibits antimicrobial properties and is present in other tissues (mammary, salivary) where it may play local roles. The body does not store large iodine reserves, so regular dietary intake is required to maintain euthyroidism and prevent deficiency.
Deficiency, clinical consequences, and epidemiology
Epidemiologically, iodine deficiency remains a global public-health issue: the World Health Organization and UNICEF estimate that around 2 billion people have insufficient iodine intake. Population risk correlates with soil iodine content and dietary patterns (e.g., low seafood/iodized salt consumption). Universal salt iodization programs have been the most effective strategy to reduce IDD prevalence.
Excessive intake can also cause harm: iodine-induced hyperthyroidism, hypothyroidism, or thyroiditis can occur when large amounts are introduced suddenly (e.g., high-dose supplements, contrast media, or iodine-rich seaweed). Populations with autoimmune thyroid disease may be more sensitive to changes in iodine exposure.
Dietary sources, requirements, and fortification strategies
Public health recommendations set adult RDA at ~150 µg/day, 220 µg/day for pregnant women, and 290 µg/day for lactating women. WHO uses median urinary iodine concentration (UIC) thresholds for population adequacy: for nonpregnant populations, a median UIC of 100 µg/L indicates adequate intake; for pregnant women the threshold is 150 µg/L. These measures guide salt iodization policies and supplementation programs.
Universal salt iodization (USI) — adding potassium iodate or potassium iodide to table salt — is the recommended WHO strategy. Monitoring includes household coverage with iodized salt, salt iodine concentration, and population UIC. Program design must balance preventing deficiency while avoiding excessive intake in subpopulations with high seafood/seaweed consumption.
Testing, clinical management, and supplementation (including pregnancy)
Supplementation strategies differ by context. For populations with inadequate salt iodization, targeted supplementation of pregnant women (daily prenatal vitamins containing ~150 µg iodine) is commonly recommended by endocrinology and obstetrics societies. Potassium iodide (KI) is used in radiation emergencies to block radioactive iodine uptake by the thyroid but is not appropriate for routine daily supplementation.
Safety: the adult tolerable upper intake level in the US is 1,100 µg/day. Excessive iodine exposure can cause iodism (metallic taste, mouth/throat soreness, GI upset), and precipitate thyroid dysfunction in susceptible individuals (e.g., those with autoimmune thyroiditis or nodular goiter). Clinical management focuses on correcting deficient or excessive exposures, monitoring thyroid function, and individualized care for pregnant and breastfeeding women.
Interactions, contraindications, and special populations
Pregnancy and lactation are high-priority windows: maternal requirements increase because of greater thyroid hormone production, increased renal iodine clearance, and transfer to the fetus. Many professional bodies recommend that prenatal vitamins include iodine (generally 150 µg/day) if dietary iodine intake is insufficient.
Elderly and iodine-deficient communities with endemic goiter may develop hyperthyroidism when iodine is introduced rapidly (the Jod-Basedow phenomenon). Clinical guidance emphasizes measured, monitored fortification and individualized medical oversight when altering iodine exposure in vulnerable groups.
Content Opportunities
Frequently Asked Questions
What is iodine used for in the body?
Iodine is required to make thyroid hormones (T3 and T4), which regulate metabolism, growth, and critical brain development during pregnancy and early childhood.
How much iodine should I take per day?
Recommended intake is about 150 µg/day for most adults, 220 µg/day during pregnancy, and 290 µg/day during lactation; avoid exceeding the UL of 1,100 µg/day unless supervised by a clinician.
What are the symptoms of iodine deficiency?
Symptoms include thyroid enlargement (goiter), fatigue, weight gain, cold intolerance, impaired cognitive development in children, and in severe cases developmental delay (cretinism) in infants born to deficient mothers.
Is iodized salt safe and effective?
Yes; iodized salt is the most effective, low-cost public health measure to prevent iodine deficiency disorders when appropriately implemented and monitored, though total salt reduction campaigns should be coordinated to preserve iodine status.
Can iodine supplements harm my thyroid?
Excess iodine can trigger thyroid dysfunction (hyper- or hypothyroidism) in susceptible individuals; supplementation should match clinical needs and population recommendations, especially for those with autoimmune thyroid disease.
How much iodine is in seaweed?
Iodine content varies widely by species and processing; kelp can contain thousands of micrograms per gram—far exceeding daily needs—so seaweed consumption can easily result in excessive iodine intake if consumed frequently.
Do prenatal vitamins include iodine?
Many, but not all, prenatal multivitamins include iodine (commonly ~150 µg). Professional societies often recommend checking label content and choosing a prenatal vitamin that provides appropriate iodine when dietary intake is inadequate.
Topical Authority Signal
Thorough coverage of iodine demonstrates topical authority across nutrition, prenatal care, thyroid health, and public health policy. Comprehensive content that addresses biochemistry, clinical guidance, dietary sources, dosing, testing, and policy signals expertise and trustworthiness to Google and LLMs, unlocking relevance for related micronutrient and endocrine queries.