How much iodine per day, and why the usable window is only sevenfold wide

1. 01

   The usable window runs 150 to 1,100 mcg, a factor of about 7

   The adult Recommended Dietary Allowance is 150 mcg per day and the Tolerable Upper Intake Level is 1,100 mcg per day, so the whole safe range spans roughly sevenfold (NIH Office of Dietary Supplements). Most water-soluble vitamins have windows measured in tens or hundreds, which is why a doubled dose is uneventful there and is not here. The tightness of this window is the organising fact of the subject, and it is the reason a single concentrated source can push intake out of range in one serving.

2. 02

   The requirement by life stage, and the two figures that change

   Infants have Adequate Intakes of 110 mcg from birth to 6 months and 130 mcg from 7 to 12 months. Children 1 to 8 years need 90 mcg per day, 9 to 13 years 120 mcg, and from 14 years the adult 150 mcg applies. Pregnancy raises the requirement to 220 mcg and lactation to 290 mcg (NIH Office of Dietary Supplements). Only two of these numbers move a household decision: the adult 150 mcg baseline and the near 50 percent uplift in pregnancy, which is the one point where a measured supplement is routinely warranted.

3. 03

   The Upper Limit tightens steeply with age

   The Tolerable Upper Intake Level is 1,100 mcg per day for adults, 900 mcg at 14 to 18 years, 600 mcg at 9 to 13, 300 mcg at 4 to 8 and 200 mcg at 1 to 3 (NIH Office of Dietary Supplements). The pediatric column is the one people overlook. A seaweed snack that is a rounding error for an adult is a different exposure for a 3-year-old whose ceiling is 200 mcg, and it takes well under a gram of some dried kelp to reach that figure.

4. 04

   The thyroid is effectively the only consumer of dietary iodine

   Iodine is required to synthesise the thyroid hormones thyroxine (T4) and triiodothyronine (T3), which regulate protein synthesis, enzyme activity and metabolic rate (NIH Office of Dietary Supplements). There is no large storage pool elsewhere and no alternative sink of consequence. That single-consumer structure is why both ends of the intake range produce the same clinical category of problem, and why the margin between adequate and excessive is narrower than for nutrients with several destinations.

5. 05

   The Daily Value is 150 mcg, so label percentages convert in your head

   The Daily Value used on Nutrition and Supplement Facts labels is 150 mcg for iodine, identical to the adult RDA, so a percentage translates directly (FDA; NIH Office of Dietary Supplements). A product listing 100 percent DV supplies 150 mcg. A kelp tablet listing 1,000 percent DV supplies 1,500 mcg, which exceeds the adult Upper Limit of 1,100 mcg on its own before any food is counted. Checking that one percentage is the fastest useful test of a supplement in this category.

6. 06

   Where the iodine actually is: white fish, dairy, eggs, iodized salt

   Baked cod supplies 158 mcg per 3 oz serving, more than the full adult RDA in one portion. Plain low-fat Greek yogurt gives 116 mcg per cup, milk 85 mcg per cup, a quarter teaspoon of iodized salt 76 mcg and one large egg 26 mcg (NIH Office of Dietary Supplements). Dairy and white fish carry most of a typical intake. Other seafood contributes as well, so wild salmon adds to the total, though far less per serving than cod does, and the dairy line is the one that moves most when a diet changes.

7. 07

   One gram of dried kelp spans the entire safe range

   Seaweed is among the best food sources of iodine and the least predictable: a single 1 gram sheet of dried kelp can contain roughly 16 to 2,984 mcg (NIH Office of Dietary Supplements). The low end is a tenth of the RDA, the high end is 2.7 times the adult Upper Limit of 1,100 mcg, from the same nominal food in the same nominal quantity. Species, harvest site, season and processing all move the figure and none of it appears on the package. This is the most important practical number in the topic.

8. 08

   Iodized salt is the predictable source, at about 45 mcg per gram

   Iodized salt in the United States contains approximately 45 mcg of iodine per gram of salt, which is where the figure of 76 mcg per quarter teaspoon comes from (NIH Office of Dietary Supplements). Two quarter-teaspoons across a day of home cooking cover the adult RDA of 150 mcg on their own. It is a modest, consistent and cheap source, and its consistency is the point: unlike seaweed, the dose per gram does not vary by a factor of 180.

9. 09

   Processed food uses non-iodized salt, so intake falls invisibly

   Processed foods almost always use non-iodized salt, and specialty salts such as sea salt, kosher salt and pink salts are generally not iodized either (NIH Office of Dietary Supplements). A household that puts away the shaker while eating more packaged and restaurant food therefore lowers iodine intake with sodium intake unchanged, and nothing on any label reports it. This is the most common silent cause of a declining iodine intake in a diet that otherwise reads as an improvement.

10. 10

    Pregnancy at 220 mcg and lactation at 290 mcg justify a stated dose

    The requirement rises to 220 mcg in pregnancy and 290 mcg in lactation, an increase of nearly 50 percent over the adult 150 mcg, at the point where the consequences of a shortfall are least reversible (NIH Office of Dietary Supplements). This is the one population in which a routine supplement is easy to justify, and a prenatal multivitamin that prints a specific iodine figure is the least error-prone route, because a printed microgram number is verifiable and a portion of seaweed is not.

11. 11

    US median urinary iodine fell from 135.0 to 103.5 mcg/L across two decades

    Across nine NHANES cycles from 2001 to 2020 covering 6,828 women aged 14 to 45, median urinary iodine concentration declined from 135.0 mcg/L in 2001 to 2002 to 103.5 mcg/L in 2017 to 2020, and the proportion below 100 mcg/L rose from 37.6 percent to 47.7 percent; medians for pregnant and lactating women fell below the adequate range in 2007 to 2014 at 138.6 and 70.6 mcg/L (Cheng et al. 2025). A parallel review attributed the drift primarily to reduced milk consumption (Daniel and Mangano 2025).

12. 12

    Status is assessed by urinary iodine, not by the blood test people expect

    A median urinary iodine concentration of 100 to 199 mcg/L in children and non-pregnant adults, and 150 to 249 mcg/L in pregnancy, indicates adequate intake (NIH Office of Dietary Supplements). Median urinary iodine reflects total intake from all sources and accurately identifies populations with excessive intake, with thyroglobulin as the complementary marker (Farebrother et al. 2019); other population measures include neonatal thyrotropin and thyroid volume (Sohn et al. 2024). One urine sample characterises a population well and one person poorly, because daily intake swings.

13. 13

    Excess causes the same thyroid dysfunction as deficiency

    An acute iodine load can produce hypothyroidism through failure to escape the Wolff-Chaikoff effect, or hyperthyroidism through the Jod-Basedow phenomenon, in susceptible people (Sohn et al. 2024). High intakes are well tolerated by most healthy individuals, but those with preexisting thyroid disease or prior iodine deficiency may react at intakes only slightly above physiological needs; the dysfunction is usually mild and transient, though iodine-induced hyperthyroidism can be life-threatening in some individuals (Farebrother et al. 2019).

14. 14

    Who is actually at risk, and where goitrogens fit

    The identifiable higher-risk groups are people who do not use iodized salt, people who eat no dairy and no seafood, people following restrictive plant-based patterns, and pregnant or lactating women, with prevalence of inadequate status in pregnancy running from 23 percent to 59 percent across studies (Daniel and Mangano 2025). Goitrogens in cruciferous vegetables and soy interfere with iodine uptake mainly when intake is already marginal (NIH Office of Dietary Supplements), so the correction is to fix the iodine rather than to drop the vegetables.

What people ask us next.

Q01

How much iodine do you need per day?

The Recommended Dietary Allowance for adults is 150 mcg per day, rising to 220 mcg in pregnancy and 290 mcg during lactation. Children need 90 mcg from 1 to 8 years and 120 mcg from 9 to 13, and infants have Adequate Intakes of 110 and 130 mcg (NIH Office of Dietary Supplements). One 3 oz portion of baked cod at 158 mcg covers the adult figure by itself, as does a cup of Greek yogurt at 116 mcg plus a large egg at 26 mcg, so the requirement is reachable from ordinary food without any supplement.

Q02

Can you get too much iodine?

Yes, and the margin is smaller than for most nutrients. The Tolerable Upper Intake Level is 1,100 mcg per day for adults and only 200 mcg at 1 to 3 years (NIH Office of Dietary Supplements). An acute load can cause hypothyroidism through failure to escape the Wolff-Chaikoff effect or hyperthyroidism through the Jod-Basedow phenomenon in susceptible people (Sohn et al. 2024), and those with existing thyroid disease or prior deficiency may react at intakes only slightly above physiological needs (Farebrother et al. 2019).

Q03

Is a kelp or seaweed supplement a good way to get iodine?

It is the least controllable way. A 1 gram sheet of dried kelp can contain anywhere from about 16 to 2,984 mcg, which runs from a tenth of the RDA to 2.7 times the adult Upper Limit of 1,100 mcg (NIH Office of Dietary Supplements). Nothing on the package resolves which end you have. Seaweed as an occasional food is not the issue; a daily kelp capsule with no stated microgram figure is, and if a supplement is wanted the sensible choice is one that prints an exact amount.

Q04

Does sea salt or pink salt contain iodine?

Generally not in any useful quantity. Iodized salt in the United States contains approximately 45 mcg per gram, which gives 76 mcg per quarter teaspoon, while sea salt, kosher salt and pink salts are usually not iodized (NIH Office of Dietary Supplements). Switching to a specialty salt therefore removes a predictable 150 mcg per day source without changing sodium intake at all, which is one of the more common unintentional ways to move iodine intake in the wrong direction.

Q05

How much iodized salt covers the daily requirement?

About half a teaspoon of iodized salt across a day of home cooking, since a quarter teaspoon supplies 76 mcg and the adult RDA is 150 mcg (NIH Office of Dietary Supplements). That is not a recommendation to add salt; it is a description of what the salt already in home-cooked food is contributing. The relevant risk is the reverse case, where home cooking falls and packaged food rises, because processed foods almost always use non-iodized salt.

Q06

Do pregnant women need an iodine supplement?

This is the one population where a routine supplement is straightforward to justify. The requirement rises from 150 to 220 mcg in pregnancy and 290 mcg in lactation (NIH Office of Dietary Supplements), and US population data has moved the wrong way, with median urinary iodine among women of childbearing age falling from 135.0 mcg/L to 103.5 mcg/L across 2001 to 2020 and inadequate status in pregnancy reported at 23 percent to 59 percent (Cheng et al. 2025; Daniel and Mangano 2025). A prenatal multivitamin with a stated iodine figure is the simplest route.

Q07

How is iodine status actually tested?

By urinary iodine concentration rather than by a blood iodine test. A median of 100 to 199 mcg/L in children and non-pregnant adults, and 150 to 249 mcg/L in pregnancy, indicates adequate intake (NIH Office of Dietary Supplements). Median urinary iodine reflects total intake from all sources and identifies populations with excess accurately, with thyroglobulin as a complementary marker (Farebrother et al. 2019). One sample describes a group well and an individual poorly, because intake varies day to day.

Q08

Do broccoli, cabbage or soy block iodine?

Only to a degree that matters when intake is already marginal. Goitrogens in cruciferous vegetables and soy interfere with iodine uptake, and the interference becomes clinically relevant mainly against a background of low intake (NIH Office of Dietary Supplements). Since the adult RDA is 150 mcg and a single 3 oz portion of cod supplies 158 mcg, the practical answer is to secure the iodine rather than to remove the vegetables. Note that fish oil capsules are a fat source, not an iodine source, and contribute nothing here.