Iodine
Also known as: Urinary Iodine
What Does Iodine Measure?
Iodine is an essential trace mineral measured primarily through urinary iodine concentration (UIC), which reflects recent dietary iodine intake. Since the body excretes approximately 90% of ingested iodine through urine, a spot urine sample or 24-hour urine collection provides a reliable snapshot of iodine status. Blood serum iodine tests are less commonly used but can also assess circulating iodine levels. The test is typically expressed in micrograms per liter (µg/L) for urine or micrograms per deciliter (µg/dL) for serum.
Why Does Iodine Matter?
Iodine is critical for the production of thyroid hormones—thyroxine (T4) and triiodothyronine (T3)—which regulate metabolism, growth, brain development, and virtually every organ system in the body. Iodine deficiency is one of the most preventable causes of intellectual disability worldwide and can lead to goiter, hypothyroidism, and serious developmental problems in fetuses and infants. Conversely, excess iodine can trigger or worsen thyroid dysfunction, including hyperthyroidism or autoimmune thyroid disease. Monitoring iodine status is especially important during pregnancy, infancy, and in populations with restricted seafood or dairy intake.
Normal Ranges
Males
100–199 µg/L (urinary iodine concentration; sufficient range)
Females
100–199 µg/L (urinary iodine concentration; 150–249 µg/L recommended during pregnancy)
Children
100–199 µg/L (school-age children); 100–299 µg/L acceptable range varies by age
Causes of High Levels
- Excessive consumption of iodine-rich foods such as seaweed, kelp, or seafood
- Overuse of iodine-containing supplements or multivitamins
- Exposure to iodine-based contrast agents used in CT scans or X-ray procedures
- Use of iodine-containing medications such as amiodarone (a heart drug)
- Topical application of iodine antiseptics (e.g., Betadine) absorbed through skin
- Excessive intake of iodized salt or fortified foods beyond daily requirements
Causes of Low Levels
- Low dietary intake of iodine-rich foods such as seafood, dairy, and eggs
- Use of non-iodized salt or sea salt, which contains little to no iodine
- Strict vegan or plant-based diets that exclude seafood and dairy
How to Improve Your Iodine
Diet
- Eat iodine-rich seafood such as cod, shrimp, tuna, and seaweed 2–3 times per week
- Include dairy products like milk (approximately 56 µg per cup), yogurt, and cheese regularly
- Use iodized table salt in moderation (about 1/4 teaspoon provides ~95 µg of iodine)
- Consume eggs regularly, as one large egg provides approximately 24 µg of iodine
- Limit excessive consumption of raw goitrogenic foods (kale, broccoli, soy) if iodine levels are low
Supplements
- Potassium iodide supplements at 150 µg/day for adults to meet the RDA; 220 µg/day for pregnant women
- Prenatal vitamins containing iodine (look for at least 150 µg per serving) for women who are pregnant or breastfeeding
- Kelp or seaweed-based iodine supplements (use cautiously—dosage varies widely and excess is possible)
- Multivitamins with iodine (typically 100–150 µg per dose) as a convenient option for those with dietary restrictions
- Avoid high-dose iodine supplements exceeding 1,100 µg/day (the tolerable upper limit for adults) without medical supervision
Related Biomarkers
Frequently Asked Questions
What is the difference between a urine iodine test and a blood iodine test?
A urine iodine test (urinary iodine concentration) is the most common and practical way to assess iodine status because the body excretes most ingested iodine in urine, making it a reliable indicator of recent intake. A blood (serum) iodine test measures circulating iodine but is less commonly ordered and can be influenced by acute fluctuations. For population studies and most clinical purposes, the urine test is preferred.
Can low iodine cause weight gain?
Yes, indirectly. Iodine deficiency can lead to hypothyroidism—a condition where the thyroid gland doesn't produce enough thyroid hormones. Since thyroid hormones regulate metabolism, insufficient levels can slow metabolic rate, leading to symptoms such as weight gain, fatigue, cold intolerance, and sluggishness. Correcting iodine deficiency can help restore thyroid function and, over time, support a healthier metabolism.
Is iodine especially important during pregnancy?
Absolutely. Iodine requirements increase significantly during pregnancy and breastfeeding because the developing fetus and newborn depend entirely on maternal iodine supply for thyroid hormone production. Adequate thyroid hormones are essential for normal fetal brain development and neurological function. Severe iodine deficiency during pregnancy can lead to cretinism, intellectual disability, and stunted growth. The WHO recommends 250 µg/day for pregnant and breastfeeding women, compared to 150 µg/day for non-pregnant adults.