Why essential
Iodine atoms are physically incorporated into thyroid hormone molecules. Without iodine, the thyroid can't produce hormones.
Deficiency
- Goiter (compensatory thyroid enlargement)
- Hypothyroidism
- Cretinism in offspring (severe deficiency in pregnancy)
- Cognitive issues
Less common in US due to salt iodization but still possible in those avoiding iodized salt.
Excess
Counterintuitively, very high iodine can produce thyroid problems:
- Trigger autoimmune thyroid disease in susceptible individuals
- Iodine-induced hyperthyroidism (Wolff-Chaikoff effect failure)
- Hypothyroidism in some patterns
Very high doses (kelp supplements with thousands of µg) are problematic.
Optimal range
- Daily intake: 150 µg (RDA), up to 1,100 µg upper limit
- Urinary iodine: 100-300 µg/L (population marker)
- Pregnant: higher needs (220-250 µg/day)
Sources and supplementation
- Iodized salt (primary source)
- Seaweed/kelp (concentrated; can be too much)
- Dairy
- Eggs
- Saltwater fish
- Multivitamins typically contain 150 µg
The clinical pearl: Don't aggressively supplement iodine without testing. Most adults get adequate intake. Excessive iodine can trigger thyroid problems in susceptible individuals.
Bottom line
Iodine is essential for thyroid hormone production. Both deficiency and excess produce problems. Most adults get adequate intake from diet. Test if concerns; supplement modestly if needed.
150 µg
RDA for adults
220-250
µg/day pregnancy
Both
deficiency and excess problematic