The easiest way to make the world smarter

The salt I buy is never just salt. It’s always iodized salt. But iodine is a poisonous element. So growing up, I was always confused by this weird combo.

Until I learned it was doing something big. By big, I mean iodized salt has saved hundreds of millions of IQ points in the US alone. And that's not even its original purpose!

Worldwide, it's considered one of the most successful public health programs ever. Now you'd expect all table salt is iodized, we get extra iodine from meat and seafood, and iodine levels are rising nicely.

Except. Only 53% of US table salt is iodized. Our main iodine sources are not meat or seafood. And this graph of real iodine levels in the US -

is backwards. There's a lot to clear up. People don't remember what life was like before salt iodization. So I got doctors, researchers, taste scientists, and even America's Test Kitchen to help.

Let's start with the basics. I. The 53rd element on the periodic table, the 60th most abundant element on Earth, and $17.99 on Amazon.

Iodine turns any starch blue or black immediately, like this bread or even the 5% of starch that's in paper. That's why it's in those pens

cashiers use to tell real money from counterfeit money. Now, this is only a 2% solution of iodine. That's because pure iodine is poisonous and reactive.

I mean, it looks like it. Instead, it's usually diluted like this. Or it's bonded with another element by getting an electron from it. Whenever iodine has that extra electron, which is also

its most common form, we call it iodide. Now this is still powerful stuff. It used to be a common antiseptic in first aid kits, and it's still used in hospitals today. But here's the twist.

We mostly interact with iodine by eating it. Not like this. Though it does sanitize water in emergencies. Following the directions from the US EPA website,

mix in five drops per liter, wait 30 minutes, and drink away. Even if it does not look pretty... or taste good. Why are we eating this again?

Well, our first clue is in the ocean, where there's 90 billion tons of it. But we don't get our iodine from there. Instead, over half the world's iodine is extracted in Chile from caliche, giant layers of mineral rock.

That's because the ocean has so much water that even 90 billion tons is still nothing. Just 0.06 parts per million. And that's also kind of the key to iodine - getting an extremely small amount,

but a critical one. In fact, it's the opposite of poison. It's the heaviest element required for biological life. But there is one place in the ocean where iodine does concentrate really well.

80,000 times as well. Iodine was first discovered because French chemist Bernard Courtois was using seaweed to manufacture saltpeter, the main ingredient in gunpowder. Very in demand in 1811, Napoleon was actively conquering Europe.

Now Courtois regularly cleaned his seaweed containers with sulfuric acid. One day he added a little too much and a wave of purple fumes billowed up, condensing on his lab surfaces into these dark crystals.

A new element. Iodine was named for its signature color. The Ancient Greek word for violet-colored is ioeides. i-ioeyedes. Yoeides. Iyoeyides.

Ioei- Doctors at the time quickly realized one thing iodine was great at was treating goiters. A goiter is a lump that forms on the side of the neck, and it can range up to the size of a watermelon.

These mysterious lumps often appeared out of nowhere with no other symptoms. Now, as a very visible condition, people have been treating these since ancient times. They just didn't know why it happened.

And, that it was just a symptom of a much bigger problem. A few years after iodine’s discovery, Swiss doctor Jean-Francois Coindet proposed

that iodine was the active ingredient in a common goiter remedy, burnt sea sponges. Yum. So he tried giving diluted iodine solutions directly to his patients to unbelievable success.

The goiters vanished in as fast as eight days. Then other scientists realized that goiters coincided with low iodine levels in soil and water, then they discovered iodine in the human thyroid,

which happened to be right where goiters popped up, and so by the 1900s, people had started to suspect that maybe, just maybe, something about the thyroid and iodine was because of goiters.

So what is this wild thing doing in our thyroids? Well, the purpose of the thyroid, which sits right here, is mainly just to produce two hormones:

T3 and T4. These go into your blood to control cell metabolism, basically setting the pace for how all energy is used in your body to grow and develop. And the key element in these hormones is iodine.

The 3 and 4 actually stand for how many iodine atoms they each have. Now the thyroid is governed by something else. The pituitary gland makes it produce T3 and 4

by releasing its own thyroid stimulating hormone, or TSH. When your blood has too much T3 and T4, it's the pituitary gland that gets the signal to release less TSH and slow the thyroid down.

But it's a tough boss. If you don't have the iodine to make enough T3 and T4, the pituitary gland never gets the signal to release less TSH, so the thyroid is left

running constantly, trying to pull any iodine it can to make the hormones, and it starts to grow. Into a goiter. Now thyroid hormones are most critical in the womb, since they help grow

all your tissues and organs from scratch, especially your brain. But fetuses don't have active thyroids until about halfway through pregnancy. So to start, the only source of these hormones is from the mother.

And if there isn't enough T3 and T4 to go around, these babies can be born with a lifelong condition called cretinism. At its most severe, cretinism means physical stunting, muteness, deafness, and intellectual disability.

Goiters now seem like nothing in comparison. But perhaps the biggest mystery around all of this was that towns across the world, from mountain hamlets to river valleys to inland cities, were filled

with cases of cretinism and goiter, while other areas had none. And nowhere had it like Switzerland.

When Mark Twain visited the country, he wrote. Well, I am satisfied. I have seen the principal features of Swiss scenery - Mont Blanc and the goiter - now for home! In some remote areas, 94% of men had goiters.

As many as 10% of babies showed signs of cretinism. But 100 years after iodine was first identified, a family doctor, Heinrich Hunziker, proposed a complete theory of goiters.

Maybe the environment caused iodine deficiency in the thyroid, and it was expanding so it could get more. I mean, he basically got it! He suggests adding iodine to the national diet.

But other doctors question him. This is a poison in high amounts. How can you ensure the same tiny portion for everyone? And Hunziker asks, what about salt?

Salt is genius for a few reasons. One: it's always available. NaCl is a rock. It's not seasonal and it does not spoil. Two: there's a lot of it for cheap.

World production is over 300 million tons a year, and the oceans contain about 5 times 10^16 tons more. Three: we generally eat the same amount.

Humans need a baseline of sodium to keep our blood flowing and muscles moving, while our taste buds set a loose upper limit. One of Hunziker’s fellow doctors, Otto Bayard, decides to test this salt idea for himself. Just before the winter of 1918,

he travels to a remote, goiter-affected village and uses a snow shovel to mix potassium iodide into salt for five families. Soon, the train to this village closes for the winter.

When he returns in the spring, no one is harmed and everyone's goiters are gone. He quickly expands this experiment to over 1000 people for six months, all with the same results.

In 1922, our humble family doctors Hunziker and Bayard, as well as 14 Swiss health leaders, form a commission to implement iodized salt nationally. They taught locals in every region of the country about iodine,

and within a year, their new salt was being sold in over half the country. The iodization of Switzerland was underway. Meanwhile, the state of Michigan had a separate issue.

The men they wanted to draft for World War I couldn't button up their uniforms. In 1917, more than 20,000 men in northern Michigan were ineligible for military service because of goiters.

It was the biggest reason for medical disqualification in the area. Things were even worse for children. School surveys revealed goiter rates of 70 to 100%. For decades, this entire northern band across the US was nicknamed the Goiter belt.

But after the war, reports of a new iodized salt reached the chair of the Michigan Medical Society, Dr. David Cowie. And the moment he heard it could fully eliminate goiter,

he got to work. For two years, he organized almost 200 statewide lectures to 26,000 people. He convinced Michigan's local salt producers they could transform the state's health without changing costs or taste.

In May 1924, all five rolled out iodized salt on the shelves. The only holdout was Morton Salt. As the biggest brand in the US, they just couldn't separate out iodized salt destined for Michigan

from all their other salt. But after May, everyone watched as iodized salt rose to 90% of salt sales in Michigan within months. Cowie success changed Morton's plans. They would simply offer it to every state in the US.

That year, they proudly announced the first nationwide iodized salt. While still no one knew why these places had goiters to begin with, the results of these twin initiatives in the 1920s were immediate.

In only a few years, goiters disappeared from Switzerland. The national rate of deaf-mute births fell from 1 in 600 to 1 in 3000, matching worldwide levels for the first time.

And since 1930, there have been zero documented cases of a Swiss child born with cretinism. In the US, without any regulation iodized salt continued to make up 90 to 95% of salt sales in Michigan.

Within ten years. less than 2% of children in the Detroit area had goiters - down over 90% from their peak. But iodization’s biggest, yet most invisible effect

wasn't discovered until 2013. Thanks to a timeline quirk, researchers were able to study 2 million men born before and after salt iodization in the US. Because exactly 18 years later were the American drafts for World War II.

Now in the draft data, they found that in the 25% most iodine deficient areas of the country, later recruits born after iodization scored one standard deviation higher on military cognitive exams.

That's the same as 15 IQ points. This averages out to a total of 3.5 IQ points for every American born at the time. If we take all the U.S. births from salt iodization up through World War II, we get a total of

180 million added IQ points. And that's only an estimate for those 20 years. Other studies in China, Albania, and New Zealand have found a similar correlation between even moderate iodine deficiency

and that subtle symptom of weakened cognition. So today, doctors don't only crown iodine deficiency as the most preventable cause of intellectual disability, but iodine sufficiency as the best thing we can do

for global general intelligence. All for 5 cents per person per year. After all, it's a tiny processing step. To make edible salt, you evaporate seawater in open-air ponds

or vacuum-sealed pans until you get the salt grains. Clean minerals off those until you're left with 97% pure NaCl, then crush it all up and send it along for packaging.

Did you catch it? Those little nozzles at the end? That's the iodine. In the US, this is just water and potassium iodide, and it's added to salt at a tiny concentration of 0.01%.

The process is so much simpler than I thought it'd be. And contrary to some claims, there is also no chemical reaction. It's just exactly what you expect. The spray just sits with the salt.

The only regional difference in this process is while colder countries tend to use potassium iodide, or KI, warmer countries use potassium iodate, or KIO3. That's because KI tends to evaporate in humidity, while KIO3 is more stable.

But they're essentially the same. KIO3 just becomes KI during cooking or in your body. The US only allows KI, but I couldn't find any rigorous reason for that. Most countries allow both.

But if you have to use KI, one way to stabilize it is with dextrose. So that's added together with it. And another ingredient often in table salt is an anti-caking agent, like calcium silicate, to keep the salt from solidifying.

Fun fact. Morton built their whole brand on this idea of keeping salt pourable even during humidity. That's why they use the Rain Girl logo and that famous slogan: when it rains, it pours.

Yeah, that's them. And it's talking about pouring salt. And now you know every ingredient in your salt. The simple change of adding just a few nozzles and an iodine compound

quickly spread around the world, and countries started enshrining iodized salt in law. Today, almost 90% of the world has access to iodized salt. This has prevented an estimated 720 million iodine deficiency disorders

in the past 30 years. Out of 196 countries in the world, 128 legally require table salt to be iodized. And once a country enacts iodization, even war or famine won't stop it

because of how available, cheap, and necessary salt is. The US never mandated iodized salt. The only legal sign of all of Cowie's work is this declaration on

every salt can, required by the FDA. Now, I would say congrats to humanity on pulling off the most successful public health initiative ever. But I can't, just yet. Because

1 billion people still don't have access to iodized salt. Over 200 million people still have goiters. An estimated 5 million babies are still born with iodine deficiency disorders each year.

And the scary part is the numbers are going up. A lot of countries started to become a little bit blasé, maybe. That's Dr. Elizabeth Pearce, one of the world experts on this subject.

All the funding sometimes gets pulled away, all the attention gets pulled away, and there have been a number of places where we've seen some backsliding. The thing is, so many chefs say we don't need iodized salt anymore.

These days, we can get sufficient amounts of iodine from natural sources. As long as your diet is diverse and full of iodine-rich foods such as seafood and dairy.

But a lot of people say, Bobby, where am I supposed to get my iodine from? Not from this salt, there's way better alternatives. That has iodine in it, however, you get iodine from plenty of other natural foods. - The history of iodized salt - It was necessary

- It was necessary for 1920s Michigan. Simply put, the modern American diet no longer needs it. Let me blow some minds. The iodine in this ham versus the salmon versus the celery versus these olives is all about the same.

Almost nothing. Like one hundredth of what you need in a day. But people survived before iodized salt. So where do we get our iodine? Back to the ocean for a second. Ideally,

when this evaporates and comes down as rain, some of its iodine gets into our soil. It's an even tinier amount than before, but if all your food comes from the soil, you're getting iodine. Unfortunately, many areas don't have soil like this

because they're far inland or they get flooded out. But you're truly hard hit if you used to have glaciers. During the ice age, glaciers tore away soil layers hundreds of meters deep, completely stripping them of nutrients.

This happened most in places where they were actively retreating. Places like Switzerland and the American Midwest. Glaciers! But if you have any iodine in your environment, what matters most is how different foods concentrate it.

Luckily, I found a national survey of iodine levels in every food in the US, and I imagine it's similar for other countries. Recommended iodine intake is at least 150 micrograms a day.

And all of these following amounts are for 100g of food, like all of these are. Most plants - like fruits, vegetables, and grains, only have 1 to 3 micrograms.

Most meat is under 5 micrograms. Fish isn’t reliable. Saltwater white fish and shellfish have a lot, but others don't even have a tenth of that. And the two class standouts are of course, seaweed and iodized salt.

At 2,100 and 5,200 micrograms. You should only be getting about a teaspoon of salt per day, so the iodine is calibrated to that. Note you can eat too much iodine, but it's hard to do on a normal diet.

You'd probably tap out on the salt before you did on the iodine. But the primary source of iodine in the US is none of the above. Almost half of our iodine intake is just... dairy.

Sure, we eat it a lot more than other high iodine foods. But why does dairy have so much iodine? Maybe unsurprisingly, some iodine is put in cow feed to prevent their own thyroid issues.

That's part of it. But remember from the very beginning of this story how iodine is an antiseptic? Well, it's used to clean cows and milking equipment, so a little bit just mixes into the milk.

I can't believe I'm talking about milking cows two videos in a row. I'm going to say it again because it's so wild. Iodine may primarily enter our diet because it's in the cleaner they use to sanitize farm equipment.

So Australia historically was very iodine deficient. In the 1980s, they did some small studies that suggested that the iodine deficiency had been fixed. And then there was this big outcry about contaminants in the milk supply.

And they removed all of the use of these iodine containing cleansers from the dairy industry. And effectively overnight, the whole country became iodine deficient. But relying on this is risky for many reasons.

Actually, one big factor in falling iodine levels, down 50% in the US over the last 50 years, is the rise of plant based milks. These have no iodine. And one group this especially impacts

is Asian women from 15 to 44 years old, the group with the lowest median iodine levels in the US.

(Yes, I really drank that milk.) (In less than 60 seconds.) (I felt strange immediately.)

(A sigh of disappointment, not refreshment.) To be clear, all those factors are totally fine if you also eat iodized salt. But this is what's holding back iodine levels today - pure sentiment. Iodized salt is almost never added

to processed food because companies worry it’ll affect taste or color, or that the name potassium iodide looks scary. And then people don't buy it at the grocery store because they don't know how important it is. The reality is, people don't remember why we iodized

salt in the first place, but it was for really important reasons. Look at how trusted chefs talk about iodized salt. I don't recommend using iodized salt as it makes everything taste slightly metallic.

This is one of the few times I'll insist on anything in this book. If you've got only table salt at home, go get yourself some kosher or sea salt right away. This is iodized table salt.

This is trash. Table salt is going to be great for the trash. You may also sometimes notice a slight bitter aftertaste. Table salt honestly, is good for nothing. But every expert I asked said, there really is not good evidence,

as far as I'm aware, that you can really taste the difference. None of our testers could tell the difference. On average, people cannot tell the difference. Online, this is the biggest debate I see around iodized salt.

Does it actually taste worse or not? So let's just do it. While speaking to Dr. Gary Beauchamp for this video, a leading scientist on both salt and taste, I learned how to run a proper taste test.

And then I called up the best food experts out there to do it with me. So I emailed America's Test Kitchen kind of on a whim. I was like, hey, I swear I've done a lot of really cool research into iodized salt

and we should do a really cool experiment. And they agreed to do it, somehow. We'll see how it goes. It is such a cool setup you guys have here. - It feels cool, doesn’t it? So you guys have this whole spirit of rigor. I mean, that's why I reached out. You guys are famous for this.

How do you guys make sure that all your tests are rigorous, what's the process? We really want to question the things that I think most people hold as axiomatic. Things that you just believe are true because they're true.

You know, things like searing a steak seals in the juices, or you know - - Is that not true? - That's definitely not true. - Whaaat? Sometimes we've got a pressing question, and the only way to really know the answer to it is to test it with actual testers.

- So we're doing this double blinded. - Yes. And mostly it’s single blinded, so the tasters don't know which sample is which, they don't know which one's different, but the double blind test means that we don't even know what,

who's getting which sample. - We've got about, how many people? - We've got ten people. - Ten people. I spoke to an expert about this, and he told me the triangle test was the way to go. And even more than that, he told me to do a double triangle test.

So one where the odd one out is iodized and the other two are non-iodized, and then one where the odd one out is the non- iodized and the other two are iodized. This feels like we're getting extra rigorous today.

Yeah. This is very challenging. I think it's B but I'm not confident whatsoever.

I feel like the third one was the different one. I think A stands out to me. I think C is the one that tasted the most different. Those all taste exactly the same to me.

So A... That is really pleasantly salty. This one tastes different. Like I don't know if these are the right words, but to me

A tastes lighter and B and C taste heavier. Okay so I'm gonna say the one that's different here is A. Also you guys have good water. Can I just say that?

Tastes mildly salty. I'm not super confident in this, but my sense is that these two were the most intense. And this one I just perceived as being slightly milder.

You know what's weird? This doesn't taste like anything I drank last time. Oh no. Last time I was sooo confident. Oh no.

Oh nooo. But okay, when I drank A I didn't feel like it was a new one. I'm gonna coin flip on C, I think.

Less intense, less intense. Okay. Less intense, more intense, more intense. I'm going to go for A is the odd one out. Okay. I’m very excited to share these results with you.

So we had ten tasters and only three out of the ten got it right. - Okay. - And neither were you. It wasn't A?

No, in the first round B was the iodized sample. That was the odd sample out. Interestingly, when you tasted B, you both had a reaction

that this one was really different. But then you, with the third sample, I think you got a little bit mixed up. In round two, there were two iodized and one non-iodized sample.

- Yep. - The test was flipped. In that test, A was the non-iodized. Oh my god I completely failed. Joe you got that one right. Four out of ten people got that one correct.

Okay, so this is pretty close to random. It's pretty close to random. We're at about 35% overall and there were ten tasters, three samples each.

- This doesn't feel like a significant result - It really doesn’t, yeah. We did our best to be rigorous, but it's a small group. So I also have the results of 34 studies on iodized salt in food. I told you this is a heated debate.

No changes, no changes, no changes except mortadella had a tiny color shift. No changes. No changes. No changes, except a single lemon flavoring got less sweet. No changes with KI but KIO3 occasionally had minor effects.

No changes, no changes, no changes. Food manufacturers. I'm looking at you. It was also good for me to remember that this isn't a yes or no question. Everything has a taste, including iodine,

it's just how noticeable is 0.01% of it in salt? So don't take our word for it. Test yourself at home and please discuss your results. The popular view on iodized salt just shouldn't be oh,

this optional thing tastes bad if it doesn't taste bad and isn't optional. Iodine deficiency can appear anywhere. 23 countries are still deficient today from Finland to Nicaragua to Vietnam to Germany.

And several more, including the US, are trending down. And the hidden story through all of this is iodine deficiency’s impact on women. In pre-iodized Michigan, women had twice as many goiters as men the whole time.

In Switzerland, they had triple. Today we know pregnant and breastfeeding women need iodine more than any other group, and they're also the most likely to not get enough. My graph from the intro is of iodine levels in pregnant women in the US,

which have fallen from a median of 327 micrograms per liter in 1971 to just 144 in 2014. That's officially iodine deficient.

Now, not to fearmonger. To be clear, mild deficiency is far from guaranteeing cretinism or goiter. And while many people are still iodine deficient today, a famous statistic of 2 billion people is out of date.

I know because I asked the study's lead author, Dr. Maria Andersson. In fact, both her and Dr. Pearce told me that you can't estimate the prevalence of iodine deficiency anymore. This is an important point.

Iodine levels fluctuate so much in a person that you can't measure it at a checkup. You can only do it across a large group and take the median, like we did for pregnant women, which levels out those fluctuations.

That's helpful to tell if the group is deficient or not, but we have no details on their actual distribution. That's why all of my stats in the video have been either for medians or for deficiency symptoms, but never for just iodine deficiency itself.

I was getting concerned I need to get my iodine tested. So you can't actually test it. - Oh you can’t test it. - It’s not like cholesterol, you can't walk into the doctor's office, there's no test you can do for it reliably. So as a consumer,

I shouldn't really be worrying about what numbers my iodine levels are at. I should just be worrying about getting - You shouldn't be measuring what number your iodine is. I shouldn't even be measuring, I shouldn’t even know - That should not be measured. I should have no idea what it is, but I should just be making sure I'm eating enough iodine.

Correct. We've come so far since the 1900s. The vast majority of people today are sufficient. Cretinism is considered almost eradicated. Humanity has pulled off a public health miracle for 100 years,

from the 1920s to the 2020s. We just need to keep it. So some last tips to make the most of your own iodized salt. When you season, you should season high and you should season dry.

Putting my fingers right over the surface of the meat and trying to sort of get it even. It's kind of hard to get it even, right? Because I'm sort of, I'm getting these - These different areas. - Right, you have these pockets.

Exactly. Whereas if I take my salt and I hold it up here and I go like this, you just get a much more even coating.

And then the other thing is that you want to season dry. You wash your hands. You come in here, you grab your salt, you start seasoning and then all the salt just ends up on your fingers.

We've got kosher salt here, which does never contain iodine. The one used for kosher salt that's so useful is for seasoning meat evenly. You want to disperse as much of the salt as evenly as possible,

and it's harder to do it with table salt. You can actually use any of these salts almost interchangeably. The biggest issue is the density of the crystals.

So this is kosher salt. But you know, kosher salt from Diamond Crystal is much fluffier and less dense than kosher salt from Morton's. Whereas table salt tends to be very generic, very tiny little uniform crystals.

So a teaspoon of table salt, is equivalent to two teaspoons of Diamond Crystal kosher salt, which is equivalent to one and a half teaspoons of Morton's. - Okay. Right. - kosher salt.

This one for your health. - And also because it's a good basic salt. - Yep. And then this one, for all the other purposes, it's nice to grab, - Exactly. - especially for seasoning meat. I really feel like the biggest determinant of salt isn't so much its flavor,

but actually its shape, its texture. It’s the same chemical structure, it's just the texture that I'm perceiving as good. - Exactly. - Perfect.

Well, that was awesome. Big thanks to my friends at America's Test Kitchen for taking the time to do this taste test with me. That was incredible. So you should definitely check out their YouTube channel below.

If you're like me, at some point in this video you started thinking, gosh, I really need more dairy. I gotta cut processed food. I should do that. I'm craving seaweed. Should I get an iodine supplement?

If you're pregnant, you really should do that. Women who are planning pregnancy, pregnant, or breastfeeding should take a daily supplement containing 150 micrograms of iodine. But for everyone else, the message is simple.

If they are adding salt to food at the table or in the kitchen, should make sure it’s iodized salt. Don't forget, the beauty of this whole public health measure is you don't have to pay for it. You don't even have to think about it.

By using your brilliant, genius, boring, regular, old iodized salt, you can get all the iodine you need in what you already eat every day.