Iodine
trace-mineral
Key Takeaways
- FDA daily value is 150 mcg; RDA for adults is 150 mcg/day
- Deficiency is the most common cause of preventable intellectual disability worldwide (NIH)
- Essential for thyroid hormones T4 and T3
- Salt iodization dramatically reduced global deficiency
- Both deficiency and excess can cause thyroid dysfunction
13
Studies Reviewed
110 mcg
RDA (Birth to 6 months)
1100 mcg/day
Upper Limit
water-soluble
Solubility
Role in the Body
Iodine is essential for thyroid hormones T4 and T3, which regulate protein synthesis, enzymatic activity, and metabolic rate. These hormones are also required for fetal and infant CNS and skeletal development. TSH regulates thyroid function. Insufficient iodine causes elevated TSH and potentially goiter. The interaction between iodine, selenium, and iron is important for thyroid health.
- Thyroid hormone synthesis (T4, T3)
- Metabolic rate regulation
- Fetal/infant neurodevelopment
- Skeletal development
- Immune function (possible)
Supplement Forms
Iodized salt
RecommendedBioavailability: 95%
Most effective public health intervention
Potassium iodide (KI)
RecommendedBioavailability: 95%
Common supplement; radiation protection
Kelp/seaweed supplements
Bioavailability: 0%
Highly variable; can be excessive. Acne risk at high doses (pmid:32941710)
Molecular iodine (I2)
Bioavailability: 0%
Less common; some fibrocystic breast research
Food Sources
Iodized salt
Seaweed (variable)
Fish and shellfish
Dairy products
Eggs
Enriched bread/grains
Deficiency
Prevalence: Global public health concern in regions without salt iodization. Common in parts of Europe, Africa, Southeast Asia.
Symptoms:
- Goiter (earliest sign)
- Hypothyroidism
- Cretinism (severe maternal deficiency)
- Intellectual disability in children
- Miscarriage/stillbirth
- Fetal growth retardation
Risk Factors:
- Iodine-poor soils
- No iodized salt
- Vegan/vegetarian diets (pmid:33341313, pmid:33801269)
- Pregnancy/lactation
- Selenium deficiency
- Goitrogen consumption
Safety & Interactions
Possible Side Effects:
- • Thyroid dysfunction from excess
- • Iodine-induced thyroiditis
- • Acne from kelp (pmid:32941710)
- • Metallic taste/nausea at high doses
Drug Interactions:
- • Antithyroid medications (may counteract)
- • Lithium (additive hypothyroid)
- • ACE inhibitors (KI forms)
Contraindications:
- • Dermatitis herpetiformis
- • Pre-existing thyroid disease
- • True iodine allergy (rare)
Frequently Asked Questions
How much iodine daily?
150 mcg for adults; 220 mcg in pregnancy; 290 mcg during lactation.
Is iodized salt sufficient?
Usually yes with a varied diet. Vegans, salt-restricted dieters, and pregnant women should monitor.
Can too much iodine be harmful?
Yes. Upper limit is 1,100 mcg/day. Excess causes thyroid dysfunction.
Research Sources
15 peer-reviewed studies analyzed from PubMed. 7 directly cited in this review.