Does Iodized Salt Make You Smarter?

Food culture loves to clown on table salt.

It is plain, cheap, old-school, and totally lacking in romance. Next to kosher salt, flaky sea salt, and pink Himalayan salt, iodized table salt feels like the least glamorous thing in the pantry. But it is doing a job those prettier salts usually are not. The nutrient involved is iodine, which in fortified salt is commonly present in forms such as iodide or iodate, and your body needs it to make thyroid hormones.

So can iodized salt make you smarter?

Not in the way a clickbait headline makes it sound. Iodized salt is not a nootropic. It does not turn a healthy adult into a genius because they shook a little extra onto dinner. The stronger, more accurate claim is that iodized salt helps prevent iodine deficiency, and iodine deficiency can impair brain development and cognitive function. NIH calls iodine deficiency the most common cause of preventable intellectual disability in the world, and WHO says even less severe deficiency can reduce intellectual capacity.

Why iodine matters to the brain

Iodine matters because it is essential for thyroid hormones, especially T3 and T4. Those hormones help regulate metabolism, but they also play a critical role in growth and development, including development of the central nervous system before birth and in early life. During pregnancy and early infancy, iodine deficiency can cause irreversible harm. In children, even less severe deficiency has been associated with lower-than-average intelligence and other neurodevelopmental problems.

That is why this story is bigger than “table salt versus fancy salt.” At its core, this is a story about one of the cheapest pantry ingredients quietly supporting normal brain development on a population level. WHO’s wording is blunt: severe iodine deficiency can cause brain damage, and less severe deficiency may still cause mental impairment that reduces intellectual capacity.

Where the IQ claim comes from

The “iodized salt made people smarter” line mostly comes from a striking U.S. natural experiment.

Researchers looked at geographic data on iodine deficiency from the World War I era and then compared men born before and after salt iodization using World War II military records. In the lowest-iodine regions, birth after iodized salt became available was associated with about a one-standard-deviation increase in average cognitive test performance. On a standard IQ scale, that is roughly equivalent to about 15 points. The overall U.S. effect was smaller, but in the most deficient places it was big.

That finding is important, but it needs to be read the right way. It does not mean iodized salt acts like a mental performance enhancer for people who already get enough iodine. It means that correcting a widespread nutrient deficiency can lift average cognitive outcomes in populations that were being held back by that deficiency in the first place.

NIH says the broader research points in the same direction. Chronic moderate to severe iodine deficiency, particularly in children, reduces IQ by about 12 to 13.5 points, and a placebo-controlled New Zealand study in mildly deficient children found improvements in perceptual reasoning and overall cognitive score after iodine supplementation corrected their deficiency. That is still a deficiency story, not a magic-brain-powder story.

Why this still matters in American kitchens

It would be easy to think this is all ancient public-health history, but the U.S. kitchen reality is messier than most people realize.

Salt iodization in the United States is voluntary. A peer-reviewed NIH/FDA/USDA review reported that only 53% of table salt sold in U.S. retail outlets was iodized. NIH also notes that most salt intake in the United States comes from processed foods, and food manufacturers almost always use noniodized salt in those foods. On top of that, specialty salts such as sea salt, kosher salt, Himalayan salt, and fleur de sel are not usually iodized. So a diet can be very salty without being especially rich in iodine.

The good news is that NIH says the general U.S. population appears to have adequate iodine intake overall. The caution flag is that some pregnant women may be at risk for iodine deficiency, and pregnancy is exactly when iodine matters most because fetal development depends heavily on maternal thyroid hormone. NIH lists the adult iodine recommendation at 150 micrograms per day, rising to 220 micrograms during pregnancy and 290 micrograms during lactation.

No, more iodine is not always better

This is the part the internet usually leaves out.

The evidence supports preventing deficiency. It does not support megadosing iodine in the hope of becoming sharper, faster, or more focused. NIH sets the adult tolerable upper intake level at 1,100 micrograms per day, and high intakes can cause thyroid problems too. In pregnancy, the story is even more nuanced: NIH’s pregnancy fact sheet says iodine supplements can help ensure adequate status, but the effects of supplementation on infant and child neurodevelopment are not fully understood, and both low and high iodine intakes during pregnancy have been associated with neurodevelopmental deficits in children.

So no, this is not a reason to start pounding kelp tablets or chasing high-dose iodine drops. The takeaway is steadier and less dramatic: get enough, not too little and not too much.

What home cooks should actually do

For most people, the practical answer is wonderfully boring: keep iodized salt in the kitchen.

That does not mean giving up kosher salt. Kosher salt is still great for seasoning meat and controlling how salt falls through your fingers. Flaky finishing salt is still great for texture. But ordinary iodized table salt deserves a place in the pantry because it covers a nutritional base that many specialty salts do not. If your household leans hard on kosher salt, sea salt, plant milks, and processed foods, iodized salt becomes even more worth keeping around.

Pregnancy is the one stage where this becomes especially important. NIH’s pregnancy guidance summarizes recommendations from groups including the American Thyroid Association and the American Academy of Pediatrics that women who are pregnant or planning pregnancy take 150 micrograms of iodine per day, alongside the use of iodized salt.

The bottom line

Did iodized salt make people smarter?

The best answer is: not directly. Iodized salt helped prevent iodine deficiency, and that likely improved cognitive outcomes in people and places where too little iodine was quietly impairing normal thyroid function and brain development. That is less flashy than a miracle-brain-food headline, but it is also more true.

And for a pantry staple that usually gets treated like culinary dead weight, that is a pretty extraordinary legacy.

Do you still keep iodized salt at home, or has it been replaced by kosher salt, sea salt, or Himalayan salt in your kitchen?

Sources

• National Institutes of Health, Office of Dietary Supplements. Iodine — Fact Sheet for Health Professionals.
• World Health Organization. Iodine deficiency.
• National Institutes of Health, Office of Dietary Supplements. Dietary Supplements and Life Stages: Pregnancy — Health Professional Fact Sheet.
• Feyrer, Politi, and Weil. The Cognitive Effects of Micronutrient Deficiency: Evidence from Salt Iodization in the United States.
• Maalouf et al. Iodized Salt Sales in the United States.
• Pehrsson et al. Iodine in Foods and Dietary Supplements: A Collaborative Database Developed by NIH, FDA and USDA.
• National Institutes of Health, Office of Dietary Supplements. The Scoop — Winter 2021.