Iodine was supposed to be a solved problem. After universal salt iodization rolled out across the United States in the 1920s, goiter rates collapsed and the trace mineral disappeared from public-health worry lists. Nearly a century later, it is creeping back. A growing body of research suggests that quiet shifts in how Americans season food, what they drink, and how they shop are nudging iodine intake closer to the deficiency line — particularly for women of reproductive age.
Why iodine matters
Iodine is the raw material the thyroid gland uses to make thyroid hormone, which sets the pace of metabolism in nearly every cell. The National Institutes of Health Office of Dietary Supplements notes that even mild deficiency during pregnancy can affect fetal brain development, while moderate-to-severe deficiency causes goiter, hypothyroidism, and the lower IQ scores historically seen in iodine-poor regions.
Iodine deficiency is still the most common preventable cause of brain impairment worldwide, according to the World Health Organization. In the United States, urinary iodine surveys from the Centers for Disease Control and Prevention show that overall intake remains adequate at the population level, but subgroups — pregnant women, vegans, and people who avoid both seafood and dairy — are drifting toward what researchers call “mild” insufficiency.
Why deficiency is making a comeback
Less iodized salt at the table
Most dietary iodine in the American food supply was never required by law to be iodized — only the salt sold in standard table shakers. Today, roughly 70 percent of the sodium people consume comes from packaged and restaurant foods, and food manufacturers typically use non-iodized salt. A 2024 review in the journal Thyroid found that the share of US table salt that is iodized has been declining for two decades, even as consumers cut back on shaking salt at home.
The rise of trendy salts
Pink Himalayan, kosher, fleur de sel, and gourmet sea salts have replaced iodized salt in many kitchens. They look more natural — and may contain trace minerals — but research published in the American Journal of Clinical Nutrition shows their iodine content is negligible. Shoppers who switched believing all salts were nutritionally similar are quietly losing a key source.
Plant-based diet shifts
Vegan and vegetarian diets remove two of the largest contributors to iodine intake in Western diets: dairy and seafood. A 2023 analysis in Nutrients reported that vegans had urinary iodine concentrations roughly half those of omnivores, putting many below the WHO adequacy threshold unless they used iodized salt or seaweed regularly.
Changes in dairy and bread
Dairy is a major and often unintentional source of iodine because cows are fed iodine-fortified supplements and farms use iodine-based teat disinfectants. Both practices have grown less consistent. Bread once delivered iodine through dough conditioners, but most commercial bakeries have switched to bromine-based alternatives.
Who is most at risk
Researchers have identified several groups where mild deficiency is most likely to matter clinically:
- Pregnant and breastfeeding women. The American Thyroid Association recommends 150 micrograms of supplemental iodine daily during pregnancy and lactation, yet surveys suggest fewer than half of US prenatal vitamins consistently contain it.
- Vegans and strict vegetarians who skip iodized salt and seaweed.
- People on low-sodium diets for blood pressure who replace salt without finding another iodine source.
- Adolescent girls and young women, who studies in the UK and US have flagged as having borderline urinary iodine levels.
Signs research links to low iodine
Mild deficiency rarely causes obvious symptoms. As it deepens, the thyroid can enlarge into a goiter, metabolism slows, and people may experience fatigue, cold intolerance, dry skin, brain fog, weight gain, or constipation — all overlapping symptoms of hypothyroidism. In pregnancy, even modest deficiency has been associated with lower verbal IQ scores in children, according to a landmark UK study published in The Lancet.
Best food sources
The NIH lists the following as the most reliable dietary sources:
- Seaweed (kelp, nori, wakame) — by far the richest source, though kelp can deliver enormous doses, so moderation matters.
- Cod, shrimp, tuna, and other seafood.
- Dairy products like milk, yogurt, and cheese.
- Eggs, especially the yolks.
- Iodized table salt — about 76 micrograms in a quarter teaspoon.
Plant-only eaters can meet needs with a small, controlled portion of nori or a daily iodine supplement that supplies about 150 micrograms.
How much you need
The Recommended Dietary Allowance for adults is 150 micrograms per day, rising to 220 micrograms during pregnancy and 290 micrograms during breastfeeding. Children and infants need less, with values scaled by age.
Can you get too much
Yes. Iodine has a relatively narrow safe range. The tolerable upper limit for adults is 1,100 micrograms per day. Sudden high doses — particularly from kelp supplements, which can range from a few hundred to several thousand micrograms per serving — can paradoxically trigger thyroid dysfunction in susceptible people, including those with autoimmune thyroid disease. Anyone with a thyroid condition should talk with their clinician before adding supplemental iodine.
The bottom line
Iodine illustrates how an old public-health victory can quietly unwind when food culture changes faster than nutrition policy. Most Americans still get enough, but a meaningful slice of the population — especially women planning a pregnancy or eating plant-only — may be running closer to the line than they realize. Keeping a small canister of iodized salt in the pantry, eating eggs or dairy when you choose to, including occasional seaweed, or asking your clinician about a prenatal that contains iodine are all simple ways to keep an ancient mineral doing its quiet, essential work.
Disclosure: This content is for informational purposes only and is not medical advice. Always consult a qualified healthcare provider before making changes to your health regimen.