Iodine Deficiency: Symptoms, Tests, Intake, Foods

Iodine is essential for the synthesis of thyroid hormones (T3, T4), which regulate metabolism, growth, and neurological development. Prolonged deficiency leads to hypothyroidism, goiter, and in severe cases during pregnancy, cretinism in the newborn. Recommended intake and safety guidelines are detailed in the NIH ODS professional fact sheet and the EFSA DRV synthesis.

Symptoms (mild deficit → severe deficiency)

Fatigue, weight gain, cold intolerance (hypothyroidism)
Goiter (visible thyroid enlargement in the neck)
Dry skin, brittle hair, constipation
Cognitive difficulties (concentration, memory), mood changes
Pregnancy: severe deficiency = risk of cretinism (severe intellectual disability, growth retardation) in the newborn
Children: growth and developmental delays

For a clear clinical overview, see the iodine deficiency disorders (WHO).

Pregnancy and early childhood

Iodine is critical during pregnancy and the first years of life for brain development. Ensure adequate intake before conception and throughout pregnancy/breastfeeding.

Tests and benchmarks

Urinary iodine concentration (UIC): the gold standard for population assessment; reflects recent intake.
- < 100 µg/L: insufficient (population level)
- 100–199 µg/L: adequate
- 200–299 µg/L: above requirements (acceptable)
- ≥ 300 µg/L: excessive (risk of thyroid dysfunction) Benchmarks from WHO/UNICEF/ICCIDD guidelines.
TSH (thyroid-stimulating hormone): elevated TSH suggests hypothyroidism; low TSH may indicate hyperthyroidism or excess iodine.
Free T4 and T3: assess thyroid hormone levels.
Thyroid ultrasound: detects goiter and structural changes.
Thyroglobulin: a marker of thyroid function; elevated in iodine deficiency.

Population vs individual assessment

UIC is best for population surveillance (median values); for individual diagnosis, combine UIC with clinical symptoms and thyroid function tests (TSH, T4).

Iodine-rich foods (and variability)

Seaweed/kelp (kombu, wakame, nori): extremely rich, high variability (use sparingly)
Fish and seafood (cod, haddock, shrimp, oysters, mussels)
Eggs, dairy products (milk, yogurt, cheese)
Iodized salt: a practical and economical source (check label for iodine content)
Potatoes (with skin), cranberries, strawberries, prunes
Fortified bread/cereals (varies by country)

Iodine content is highly variable depending on soil, water, and fortification practices. For precise values: USDA FoodData Central, Ciqual table.

Doses and tolerance

Recommended daily intakes

EFSA (PRI): ~150 µg/day (adults), ~200 µg/day (pregnancy), ~200 µg/day (breastfeeding). See the EFSA DRV synthesis.
NIH ODS (RDA): 150 µg/day (adults), 220 µg/day (pregnancy), 290 µg/day (breastfeeding) — detailed guidelines.

Upper limit (UL)

UL (adults): 600 µg/day (from all sources, including supplements), according to the NIH ODS fact sheet. EFSA aligns broadly with this order of magnitude in its DRV opinions.
Why: limit the risk of thyroid dysfunction (both hypo- and hyperthyroidism) at very high doses.

Interactions and precautions

Thyroid medications (levothyroxine, anti-thyroid drugs): discuss iodine intake with your healthcare provider.
Goitrogens (raw cruciferous vegetables in very large amounts): can interfere with iodine utilization; normal dietary intake is not a concern.
Selenium: adequate selenium status supports thyroid function; balance is important.

Practical advice

Anchor intake through diet (fish, seafood, eggs, dairy, iodized salt). If needed, a moderate supplement (e.g., 150 µg/day equivalent) can be discussed, especially peri-conceptionally (target 220–290 µg/day total during pregnancy/breastfeeding). Evaluate thyroid function if symptoms arise.

FAQ

Is urinary iodine testing sufficient? Useful for population surveillance, but influenced by recent intake. For individual diagnosis, combine with clinical symptoms and thyroid function tests.

Iodized salt vs supplements? Iodized salt is practical and economical for most people. Supplements are useful if dietary intake is insufficient or during pregnancy/breastfeeding.

Can you over-supplement? Avoid exceeding 600 µg/day (UL). In some individuals, high doses can cause thyroid dysfunction (both hypo- and hyperthyroidism).

Who is most at risk? Pregnancy/breastfeeding, regions with iodine-poor soil, vegan diets (if not using iodized salt or seaweed), people avoiding dairy/fish.