What's the deal with fluoride?

21:33Emily Oster:Those are all to kill bacteria. People don't complain about chlorination of water very often. Orthophosphates and polyphosphates to prevent pipe corrosion. Sodium hydroxide in acidic water. Sulfuric acid in alkaline water. You got to get the pH right. aluminum sulfate as a flocculent to get all the little pieces of dirt and things to precipitate out potassium permanganate to precipitate out iron oxides so you don't get rust colored water. So there is a lot and nobody is going to town halls demanding that we no longer chlorinate the water supply because if we stopped doing that, everyone would get bacterial infections and die.

22:09Yeah. I think what does differentiate fluoride from these other things is that fluoride is not there to clean the water and to make it so you don't get poop diseases from it. It is added because we think it is good for people's teeth, basically. I mean, we can get more into that, but it's added as a kind of this is something to benefit you as opposed to without this, your water will make you ill.

22:35Emily Oster:Yes, that's a great distinction. It seems more optional. No one is interested in fighting about chlorine because if you took that out, we'd all be really sick. It seems more optional. And also there's the psychological, like something is being done to me. Even though you're ingesting the chlorine from the water and the potassium permanganate from the water, like the intention isn't there, I think is what you're saying. And there's something about the intentionality of fluoride that gets people's hackles up more. Yeah. That's my feeling. Although it's hard to get inside people's head. And, you know, could we generate a bunch of panic about something called orthophosphate?

23:14Like, probably. That doesn't sound good. So maybe that'll be our next episode. Yeah. What about the children being exposed to orthophosphate? What about the children and the pipe corrosion or whatever? Okay. So before we get into the details of this, let's talk about how we know that fluoride is good and where this initially came from.

23:38Emily Oster:It's such an interesting story. So the history of fluoride in medicine goes back to 1901 and Dr. Frederick McKay, who was looking at a condition which was called Colorado brown stain from Colorado Springs, Colorado. These were people that had brown stains on their teeth, but McKay made the insight that they actually had a really low rate of cavities. The teeth kind of were ugly and had these brown stains on it, but they just didn't get cavities. It was not entirely clear what was protecting them until 1931 when H.V. Churchill at Alcoa used spectrographic analysis to determine what was in the water at Colorado Springs and discovered it was fluoride.

24:20Emily Oster:And the levels of naturally occurring fluoride there were very, very high, about 13.2 parts per million in the brown stain affected areas. We're going to talk a lot about the dosage of fluoride in the water. So it might be worth just like, let's just set the stage now. And I'll try to give round numbers, but like 10 parts per million, this sort of Colorado brown stain is a lot. The target in fluoridated water is 0.7 parts per million. So like a 10th of that. And one of the key insights is that fluoride will protect teeth without causing stains at low doses. And then it can cause white stains, fluorosis at about three to four parts per million.

25:04Emily Oster:And then really excessive fluoride can cause these brown stains once you get up to 10 parts per million or so. Okay. So in 1942, that's when they did the dose finding study to figure out that low doses of fluoride would be protective of teeth. And then 1945, the first community water fluoridation happened in Grand Rapids, Michigan. And I just want to pause. I want to pause you on the, because I think one thing that's worth saying is, well, how did you know, how do they know about the dosing here? And the answer is that there is a fair amount of naturally occurring variation in how much fluoride there is in water across space.

25:42There are parts of the world, China, India, where actually the fluoride levels in water are very high. Obviously, Colorado Springs is very high. There's also variation in other places. So many people live in areas where the naturally occurring water fluoride in the water is higher. They use that to figure out basically how that relates to teeth health.

26:01Emily Oster:It's such a good point. And when community water fluoridation happens, they're not adding just like a random amount. They're getting the level up to 0.7 basically. 1945, Grand Rapids, Michigan is the first community water fluoridation at one part per million, a little higher than we do today. Muskegon was sort of a control community nearby. And compared to Muskegon, cavities went down by 50 % in Grand Rapids, Michigan over the next 15 years. So pretty effective public health intervention. It was 1950 when the United States Public Health Service endorsed fluoridation. I remember when we used to have a public health service.

26:39I still have it. It's just...

26:41Emily Oster:And 1955, when the first fluoride toothpaste was introduced to the market. Do you know what brand got there first? Crest. Crest. Crest toothpaste. By 1975, fluoride toothpaste was sort of everywhere. The more interesting history is probably recent. So in 2024, a federal court found, quote, unreasonable risk of fluoridation under the Toxic Substances Control Act and ordered EPA action. That ruling was subsequently vacated by a higher court. But in the interim, both Florida and Utah enacted statewide fluoridation bans in 2025. And so what you see over the past century and plus is a burgeoning understanding of the protective power of fluoride, a broad public scale adoption, and a much more recent backlash and sort of reducing of fluoride.

27:41Yeah. And I think in the current moment, it's kind of hard to overstate how much anxiety people have about this and how much you hear about this on certain corners of the internet. You know, it does have the flavor of, you know, they're adding the water to, fluoride to the water to poison us. And also just the general flavor of like, this is something to be very worried about. Like your children may be damaged by this fluoridated water in some very meaningful way. And people are afraid. And that is then what drives some of these court decisions.

28:17Emily Oster:It absolutely is what drives it. I mean, no one's saying like we love cavities. This is all about neurodevelopment and IQ. And it's a place where you can put photos that totally freak people out. So like fluoride is added to your municipal water by adding small amounts of, I don't know, like it's a mineral. So like rock crushed up rock mineral fluoride rocks, they cut and they come in bags and you can't just like eat bags of fluoride. You know, they're dangerous. It's a dangerous toxic chemical at high doses. And so those bags have, you know, skull and crossbones on them or whatever is marked for poison.

28:53People are like, look at this, they're adding poison to your water. It's like, well,

28:57Emily Oster:like, yeah, so does the potassium permanganate and the chlorine. Yeah, exactly. Like don't eat that out of the bag. Not a nerd dummy cluster. That is a disingenuous argument. But I think it's - But a very, very compelling one. Very compelling. Yeah. The dose makes the poison, as the toxicologist will tell you. And we're going to get to the IQ studies. I think it's important that we actually go through them with a little more depth. And here's a picture of the big bag of fluoride with a skull and crossbones on it. But first, because we love science so much, I think I always want to leave people out of these with an understanding of how science is cool.

29:34And if you understand the science, you can appreciate why you would do something. So fluoride helps your teeth by improving the enamel, basically.

29:46Emily Oster:It's really fascinating. So enamel, which is the protective covering on your teeth, has a crystal in it, a crystal structure called hydroxyapatite. And fluoride integrates into the hydroxyapatite crystal just through regular chemistry. That makes it fluoroapatite when the fluoride is integrated there. And fluoroapatite is a little denser than hydroxyapatite. It's less soluble. But the critical part is that enamel can dissolve at a low pH. Anyone ever dissolve a tooth in Coke for Science Fair project? Yep. No, but I totally could because my son apparently is saving all of his teeth in a small container that I found the other day because he's away at sleepaway camp.

30:30There's just like a little container in his bathroom of all of his baby teeth.

30:33Emily Oster:Oh, he's saving his teeth. Yeah, I don't even know where – like I thought I was supposed to take them, but we moved away from the tooth fairy when he figured out it wasn't real. I just Venmo him. And so I guess he's keeping the teeth. I don't know. I love it. Do you use the fairy emoji though on Venmo? I just sometimes I leave them a note that's like I added some money to your... Oh my God. So yeah, so enamel dissolves at a low pH and bacteria in your mouth release acid. And after you eat and the bacteria is sort of growing and stuff like that, the pH gets around to five in your mouth. Now, hydroxyapatite will start to dissolve around 5.5 pH, but fluoroapatite doesn't start to dissolve until a pH of about 4.5.

31:25Emily Oster:So that's one pH unit. That's actually a tenfold difference in acid concentration because it's a log scale. So it makes it much more resistant to acid. There's also some thought that there's some antibacterial properties of fluoride as well. But bottom line, this is well described. we know how this works. So the question is no longer like, does fluoride truly protect teeth? Like we know it does. The question, and I think the question more people have now is, okay, I believe you that in 1945, maybe it was important to add fluoride to the water because that was the only way people were getting fluoride and et cetera.

32:03Emily Oster:But now we have crest and other forms of toothpaste. And so, you know, do we still need to be fluoridating the water supply? I think this is, I think, genuinely an interesting question, because, of course, an intervention like dumping fluoride into the water supply is in some very, very effective, but in some ways a somewhat coarse intervention. And over time, you could imagine saying, you know, well, everybody's got fluoride in their toothpaste now. And so we don't need to be using this other mechanism. And if there's no purpose in this, then we shouldn't be doing it, which of course is generally true.

32:42For me, this is an interesting skeptical case. It's probably the most interesting of the skeptical cases. You know, not so much is this harmful, but literally just is it necessary? And I think the honest answer you're hearing, I'll go through some studies. I think that the honest answer is there is not an airtight case as airtight a case now as there was in 1945. So we have some suggestive evidence. So for example, there's a paper in the Journal of Dental Research from 2018. It takes the NHANES, which is a large nationally representative study that's used for many things, and it compares kids who live in counties with higher fluoridation versus lower, and the kids in the high fluoridation counties have fewer cavities, about 30 % fewer cavities than the others.

33:36The issue is that these counties are really very different. They tend to be different in sort of how rural versus urban they are in their income and all kinds of other things that are also potentially driving cavities.

33:47Emily Oster:And hey, flag that thought because it's going to come back when we talk about IQ differences and things like that. This entire literature on both sides is rife with residual confounding, our favorite topic. One of the things that the sort of anti-fluoride groups talk about a lot is the Cochrane Review on water fluoridation. So Cochrane, for those of you who don't know, is really the gold standard of the meta-analysis world. They're a very rigorous group that puts together meta-analyses, so combining multiple studies into one overall analysis to make big, important statements about all sorts of healthcare stuff.

34:27Emily Oster:And there is a Cochrane review on fluoridation that gets cited a lot, where they say that there is no evidence that the fluoridation of water supply after 1975 had a meaningful effect on cavities. So 1975 is the sort of arbitrary-ish marker in time when like, okay, now there's fluoride toothpaste everywhere. Everyone has access to fluoride toothpaste if they want it. So people trot that out and like, okay, there it goes. After 1975, there's no effect, so we're done. However, it's really important to know - There's no data. There's almost no data after 1975. There's almost no data. The Cochrane Review focuses on the initiation of fluoridation in a water supply.

35:07Emily Oster:And the truth is that very few places both initiated fluoridation after 1975, most had already done it, and also studied it and published it in a paper form that Cochrane could use. And so there were only two studies that actually met their criteria for a post-1975 fluoride initiation. The confidence intervals around the effect size are incredibly wide. So this is one of those, like, we just, like, the evidence just isn't there one way or another, as opposed to it doesn't really work. And you don't get that nuance when people talk about on Instagram. Yeah. I mean, just to be clear, we have randomized trials of toothpaste and tooth varnishes and things on your teeth for fluoride.

35:49So it's very clear that that reduces cavities. This is really a sort of more epidemiological question. And a big piece of the problem with these studies is that when everybody has fluoride in the water, then there is no introduction of them and then you can't evaluate. But what you can do a little bit and where I think the evidence is potentially more helpful for the value of fluoridation of your water is the places that stopped doing this. Yeah.

36:18Emily Oster:Like Florida and Utah are about to be. Yeah. Like Florida and Utah are are about to. And so I think that you can imagine, you know, on the beginning side, we have this very good evidence from what happened when you first introduced fluoride to the water from zero. Now everybody has it. So the only way you're really going to figure out if it works from this point is if you turn it off. Yeah. And there are some places that have done that. So So Calgary stopped fluoridating their water in 2011, and they saw, compared to Edmonton, these are places in Canada, apparently. Very nice places. Love you, Canada.

36:57They saw their cavities increase. Not enormously, but somewhat. And we see sort of similar things in some places in Alaska and in Israel. So Israel banned community fluoridation in 2014. And they actually saw about a doubling of child dental visits afterwards based on a time trend analysis. And so again, time trends, you know, people can always quibble. But I feel this is much stronger evidence than, say, comparing kids within fluorided versus not fluorided areas.

37:30Emily Oster:And it also answers the public policy question better, which is, you know, if people are talking about if your municipality is debating whether or not to stop fluoridation, well, we have evidence of what happens when you stop fluoridation and broadly the rate of cavities goes up, even in the modern era. There's one other thing before we move on from this, does toothpaste do the job well enough that I want to talk about that I think maybe doesn't get brought up enough, which is that there are substantial disparities in dental care in the United States in particular. Insurance coverage for dental procedures is poor, even at the best of times, and for many people, they essentially have no dental coverage.

38:15Emily Oster:I think we take it for granted sometimes that everyone has access to fluoride toothpaste and has a home environment that is encouraging and has the ability to get people to brush teeth frequently. And parents are around to make sure their kids can brush their teeth before they go to bed, as opposed to being off at work and leaving kids with a sitter and all these kinds of things. And so I think that if fluoridation stopped in my area, my kids would be fine because they have their fluoride toothpaste and they go to the dentist every six months and they get cleanings and they can get their fluoride varnishes.

38:55Emily Oster:And even if they have a cavity, we'll pick it up quickly and it'll get filled quickly and everything will be fine and they'll probably be fine. And that's just not the case for all kids. And one of the, I'm going back to my sort of concern about this pushback against public health is that hyper individualism when it comes to healthcare decisions tends to leave people behind that don't have the same privileges that other people do. Totally. I mean, I think, yeah, I was, I was, my brain was in the same place on the thinking about vaccines that, you know, when we limit the access to basic public health interventions, the people who lose are disproportionately people who are, have fewer or other resources to make up for those losses.

39:38And this is a very, very clear place where there is a huge, huge relationship between your socioeconomic status, your parental education, your parental income, and aspects of your dental health. Yeah. Where fluoride can fill in when some other things are not there. Absolutely.

39:56Emily Oster:Safety net fluoride, basically. Safety net fluoride. You know, I just said, oh, hey, I can deal with a cavity. To be fair, my kids are not psyched about having a cavity at the dentist and getting, you know, Novocaine and getting a tooth drilled. But I have certainly heard people say, look, cavities are fine. We can deal with that. There's no, it's not that bad, essentially. And Emily, we have some data, you know, it's probably, obviously we're not randomizing kids to cavity versus no cavity, but there are some adverse downstream effects of dental health. There are some correlations between. Okay.

40:32Emily Oster:Talk to me about correlations. Yeah, there are some correlations between dental problems and poor academic performance and school absenteeism. These are correlations. They aren't causal. I think the strongest arguments in favor of better fluoride, better dental care are that it improves people's teeth and experience of being in the world with their teeth. and there's actually some long-term illness things that relate to bacteria in your teeth. So there's definitely a strong correlation with academic performance. I read that as a reflection of who has access to dental care rather than a reflection of your cavities directly impacting your test scores.

41:13Emily Oster:Fair enough. That's really the benefit of fluoride. Boy, it's good for your teeth. It's really good for your teeth. I don't think that's what people want to talk about. Nope. No. People want to talk about the brain. They want to talk about the concern. And this is the core issue here is the concern that fluoride exposure, especially during pregnancy and in early childhood, is associated with lower IQ. That is the core thing that people are talking about. That's what people hear, and that is where we want to spend some time and give a fair hearing to after the break. We all miss the 90s, the music, the shows, the outfits, and without a doubt, the snacks.

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44:02Emily Oster:That's this according to Oculus Speed Test Intelligence. Date a second half of 2025. All rates reserved for T-Mobile. Money back guarantee within 30 days of cancellation. All right, we're back talking about fluoridation and IQ. And there are a lot of studies out there. There are a lot of problems with studies on both sides of this issue. But I think to give all the data a fair hearing, it's worth talking about the studies that get sort of trotted out the most often so that we can dig into them a little bit. And I want to start with the quote unquote Harvard study. You'll hear this referred to as the Harvard study.

44:38Emily Oster:This is a study that appeared in environmental health perspectives in 2012. And just a little bit of an aside, a little bit of inside baseball here, just because an author works at Harvard doesn't make it a Harvard study. Like when I publish a study, it's not the Yale study. It's like, it's my own work. Okay, so this is not like an official Harvard. What would make it the Harvard study? I mean, I feel like if Harvard commissioned like a study and they, you know, but no, this is just a lab at Harvard. It's just a study. It's just a study. Yeah. Okay. And as a Yale guy, I just take issue with it.

45:15Emily Oster:And a former Harvard guy. All right. The Harvard study is a meta-analysis of 27 studies looking at fluoride exposure and IQ in children. And the big take-home that people will say about this study is that kids with a high exposure to fluoride had a roughly 7-point lower IQ than kids with a lower exposure to fluoride. So we've got similar to what we talked about before, you know, looking at places in the world and differences in IQ, a correlation, not a causation. But, hey, it's the Harvard study. Fluoride reduces IQ. Emily, tell me a bit more about the issues of the Harvard study. So I think the important thing to understand about this study is where most of these, the studies that make up the meta-analysis come from and what the water levels look like.

46:16So, you know, we're talking, we talk about fluoridation in the U.S. We're talking about 0.7 parts per million. And that's kind of where people are aiming. this meta-analysis, mostly combining studies that are run in parts of rural China that actually have very high levels of groundwater fluoride. So this is not places where they're adding fluoride to the water. It is places where the underlying rock is full of fluoride. Actually, the underlying rock is also often in these cases also full of arsenic and lead. These are places with some iodine deficiency. There's other kind of mineral differences.

46:49Emily Oster:Which often go together, by the way. Which often go together. Yeah. Groundwater fluoride and groundwater arsenic and groundwater lead are correlated, particularly because of industrial runoff. But the fluoride levels in this water are very high. And so when they're estimating these impacts, they're effectively saying, how many IQ points, what's the effect on IQ of increasing fluoride from an already high level to an even higher level? And that is not really necessarily the relevant question for what would happen if we have small amounts of fluoride. And like with many things, and this is the core underlying point, like with many things, the dose makes the poison and very high levels of fluoride could be dangerous or could be problematic for development, while lower levels might not be.

47:39And this study is really largely focused on these higher levels, even putting aside the arsenic-led correlations.

47:47Emily Oster:Very well said. These ecological studies, the broad term here is an ecological study where you're looking at an area, really a geographic area. You have an estimate of fluoride exposure in the area. You have an estimate of IQ in the area. You're correlating those two things. It's lower quality evidence, but we do have some, I think, slightly higher quality evidence. There are studies that try to measure fluoride exposure more directly, often with urinary fluoride. And so I want to talk to you about this study that appeared in JAMA Pediatrics in 2019. This is one of the more recent studies that used urinary fluoride.

48:24Emily Oster:It was called the Murex study, 601 mother-child pairs across six Canadian cities. And what they found was that an additional one milligram per liter of fluoride was associated with a 4.5 lower IQ points in boys, although no association in girls. It's a little hard to understand why there'd be an effect in one group, not another. Emily, how do you interpret the MIRX study? I find the patterns in this study pretty problematic for reasons that this is a kind of study where I read it and I can see like 50 different problems. And it's not just one problem. Sometimes you look at a study, you're like, oh, here's the one issue.

49:13This study has many issues. So the exposures here are mostly low. There are a few very high exposure areas that kind of seem to drive all the results. The estimates are very, very sensitive to adjustments for other family differences, which suggests that there's other stuff going on. There's really no reason to think that any kinds of effects here would appear in boys and not for girls. So that's just like feels a bit like what we call P hacking, just trying a bunch of different subgroups or cherry picking your results. And it's a very small paper. You know, it's a few hundred subjects. I don't find this to be a very compelling paper for a lot of reasons.

49:52Emily Oster:But it does get – it gets brought out all the time. It's got a lot of traction. So a couple of things. First, urinary fluoride because I'm a kidney doctor. It's about urine. Guys, buckle up. Perry's got feelings about the kidneys. Just fast forward 10 minutes if you want to skip this part. No, no. It's not going to take that long. No, urinary fluoride is actually not, in my opinion, the best measure of fluoride exposure. sure. When you measure anything in the urine, you have to account for urinary concentration. So the concentration of urine can vary from roughly 100 milliosms per liter to 1 ,000 milliosms per liter.

50:27Emily Oster:So that's a factor of 10, just based on how concentrated your urine is. Many of these studies will adjust for some other proxy of urine concentration, like specific gravity. I'll just tell you as a nephrologist, specific gravity is not a great concentration marker in the urine. Some use osmolarity, which is a little bit better, but at least they think about this. Fine. What no one ever thinks about is urinary pH. So urine fluoride excretion is pH dependent, how acidic your urine is. And the way it works is that in a acidic urine, 95 % of the filtered fluoride is reabsorbed before it gets into the pee that comes out of your body.

51:14Emily Oster:Okay. So, so if your urine is acidic, you're absorbing a ton of fluoride. In alkaline urine, only 45 % is reabsorbed, which is a dramatic difference. And so that means that the pH of your urine can really drive any finding in urinary fluoride that you want. And I literally never seen a paper that adjusts for urinary pH. I don't know if the researchers are aware of it, But okay, guys, FYI, you've got to adjust for urinary pH. And a lot of things affect urinary pH, including diet, right? Like when you last ate and what kind of food, and if you have more vegetables or meats or all kinds of things that could be salient here.

51:53Emily Oster:So okay, everyone can come back now. I'm done talking about pee. I think what's, okay, so what's interesting about this, and I like very much, I don't ever think about urinary pH. It's totally right. I've never, literally never even heard of it until right now. But I think what this illustrates that I think is useful in many of these studies is they can seem, by saying we measured the fluoride in the urine, it seems better. Like it seems a lot better than saying, you know, we looked at it in the water. Estimated it based on - Estimated. It's like, oh, it's a bite. It's like when people do brain scans.

52:28It's like, ooh, we looked at the brain. Like so fancy. It's like a fancy metric. But actually all of those metrics in this particular case have some of the same problems that any measure would have. You know, it's correlated with diet. It's correlated with other characteristics. So just because something seems like a more sciency measure doesn't actually mean it's a better measure or a more accurate measure or less subject to bias. Thank you for coming to Perry's TED Talk about urine. So I think this literature, you can sort of tell from some of this discussion, is actually a bit confusing to people because we're saying, okay, there's this one study, but the things are kind of big.

53:08And there's another study, but we don't like urine. And also I have some vague complaints. For me, there is one kind of very nice paper that helps me organize this, which is a meta-analysis from 2023, which took many of these studies of water fluoride and just did this kind of quite simple thing, but separated the studies into two groups. One was studies that were in high fluoride areas. So these are areas where the underlying level is high, and then they estimate what happens when you increase from there. And then -

53:48Emily Oster:Like the India and Chinas of the world, where there's just a lot of fluoride around. Yeah. And then also sort of separately looked at the set of studies that were comparing, they were looking at the impacts of moving fluoride from a low level, many of these in Canada and Mexico. And what happens in the data, you see this, is that the high areas, it looks like when you add more fluoride, it's bad for IQ in particular for development because you're already at this high level. But at these low levels, at lower levels, the variation does not seem to relate to IQ, which is exactly what you would expect if this is bad for you at very high doses, but not at lower doses.

54:32Emily Oster:Once again, the dose makes the poison. How are we doing in the US? What percent of our fluoride is high? It's very, very low. The CDC had a report in the kind of 2016 to 2021 period. And they looked at, you know, what share of the time was the water level above two milligrams per liter? And that is pretty high. And so you would want to bring it down. But they found that happened in 0.01 % of the cases that they looked at. And just to be clear, even in those cases, it's not that the water is always at this too high a level. These waters get fixed when they are too high. That's part of why you monitor a municipal water system.

55:17So it's really unlikely that people in the US are being consistently exposed to fluoride at levels that are consistently too high. Actually, if anything, the CDC found sort of systematic errors in the other direction.

55:31Emily Oster:Too low based on targeting. A lot of the studies that show these effects are cross-sectional. So they're measuring urinary fluoride and IQ at the same time. or maybe just once over at a certain age. I just wanted to call attention to the Broadbent study, which appeared in the American Journal of Public Health, just a really elegant piece of epidemiology, which you often don't see, where they followed everyone born in Dunedin, New Zealand, between April 1972 and March 1973. Every single person who was born that year got enrolled in this study in this town, which is so cool. And they followed them for 38 years, longitudinally, like big part of their lives.

56:14Emily Oster:And they were measuring prospectively fluoride exposure, and they had repeated IQ testing. And in that broadband study, there were no differences in IQ based on fluoride exposure. So repeated high quality measurements over time. Again, you can find studies on both sides of this issue, but I just wanted to make sure there's some balance that It's not like every study, even though they're bad, finds a finding. Yeah. I mean, I think just my big general takeaway from this is it is true that high fluoride in water, like endemically high fluoride, seems to have some negative impacts on IQ. The levels that we have in American tap water do not seem to have those effects.

56:57And quoting the first one doesn't make the second one true.

57:01Emily Oster:I certainly agree. But I will say I'm not even sure that the high fluoride levels affect IQ. Honestly, I don't have a great mechanism for that. Like I don't know why that would be. And secondly, there's just so much confounding when, you know, you're living next to an industrial runoff site. So your groundwater fluoride levels are spiking. Yeah, that is a very fair point. I also, let's talk about kids' IQ because this is how this always gets framed. And Emily, this is firmly in your wheelhouse. If we really care about IQ in our children, is fluoride the only lever we have to pull? Or have there been other studies, ideally randomized studies, that would suggest that we can move the needle on IQ in kids, broadly speaking?

57:48There are many studies that suggest that we can move the needle on children's IQ and children's development. They range from, in low resource environments, some very basic stuff. like micronutrient supplementation, like improved iodine. Like, let's talk about other metals that we enjoy. You know, iodine supplementation can be helpful if people are truly deficient. And then all kinds of evidence on, you know, early childhood education, better preschool access, Head Start, you know, support for parents. Like, there's so much that we could be doing overall to improve IQ that would have potentially much larger impacts than not giving people fluoride, which is like a crazy...

58:40Yeah.

58:40Emily Oster:The only difference is that stopping fluoridation costs nothing. At least it doesn't cost the government anything. It might cost us in terms of public health, whereas all of these other interventions, you have to have an item in the budget, right? But this is high quality data. We have randomized controlled data that suggests nutritional supplementation for kids at high risk will improve IQ in the long term. Look, we have randomized data that reading to kids improves their IQ. That is a well-documented fact. And you know who helps with that? Dolly Parton. Do you know that Dolly Parton has a program where every kid in Tennessee gets – she has a whole thing where you can get free books by Dolly Parton.

59:25Like Dolly Parton is doing more for kids IQ, like by a billion margins than any even potential a floor eye thing. It's like, why aren't we more focused on Dolly Parton?

59:35Emily Oster:I think anyone can get a free book from Dolly Parton. Not just in Tennessee. Anyone. You can get a free book from her and you can read it to your kids. And that would be amazing because she's the best. She's the best. She's so great. Thank you for saving our children. It's like the greatest thing. Okay. This is now a Dolly Parton fan. There we go. So let's just touch on the little bit wackier stuff that I've seen from the influencers, which is that fluoride will calcify your pineal gland, which is actually the third eye, which gives you your psychic powers. And really the reason for fluoridation is that it's to tamp down our psychic abilities.

1:00:10Emily Oster:Now, I will admit that I have no psychic abilities. And so maybe that's why. I have some. I have some. But that's – it's because my tooth hygiene is kind of limited. How would one show that psychic abilities, which are made up, are affected by fluoride? Oh, Emily, boy, did I look. I was like, there's got to be some wackadoo journal. There's got to be some wackadoo journal. And I literally – I couldn't find anything on psychic abilities. I did find – yes, your pineal gland – I should say. The pineal gland secretes melatonin, which is the like sleepy chemicals. That's good. And it does calcify as you get older.

1:00:50Emily Oster:It is a part of the brain that is particularly prone to this. About 60 % of people based on autopsy studies will have a calcified pineal gland, and it can contribute to sleep difficulties in people in their later life. There is no evidence that fluoride accelerates this process. It's just other aging stuff that does it. However, the crystal that forms in your pineal gland is hydroxyapatite. Same thing for the tooth enamel. And fluoride binds to hydroxyapatite. So if you test it, you'll find fluoride there, but it's the same reason that you find fluoride wherever hydroxyapatite is. It's not affecting your psychic ability.

1:01:30Emily Oster:Obviously, everyone knows that psychic ability lives in the suprachiasmatic nucleus. What is that a reference? I can't even, I'm not even going to get into it. From the sleep episode. That is the central control of circadian rhythm. I thought we were like back to Star Trek. Oh, no. What is psychic ability in Star Trek? I don't even know. Okay, moving on. Okay. I want to put this all together in a way, like I want to give respect to the people that study the impact of fluoridine kits. I don't want to dismiss it. I think there's a tendency in science circles to be like, that study was bad or had a flaw or wasn't perfect or wasn't how I would do it.

1:02:08Emily Oster:And therefore I can disregard it totally. And I don't think that's fair. The way we need to interpret science is based both on the effect that is posited, right? The estimate of impact of the thing and the quality of the research. And I think the problem that people have here is that when the effect posited is bad or concerning or makes you uncomfortable, like affecting the brain of a developing child, right? There's a real ick factor there. that we tend to ignore that we should interpret that in the context of the quality of research. We're willing to accept a worse study with a bigger effect or a worse seeming effect than we would a better designed study with no effect or a not gross or icky effect.

1:03:02And I think that's a

1:03:04Emily Oster:problem and I bet there's an economics term for it, but I'm not sure what it is. Not exactly. I mean, I think it is a problem and it encompasses a bunch of issues that people have with cognition. I think one of them is just the idea of sort of salience. So once you tell people, you know, there's like this might affect your kid's brain, like it's kind of living in there and I can't sort of take it out. It just makes that fear very salient and real to me and then hard to subject to a basic rational risk-benefit calculation. I also think this is a place where it's difficult to see either the risks or benefits for real.

1:03:47Let's say something did lower your kid's IQ by one point. You would never know. That's not a meaningful amount. Yeah.

1:03:52Emily Oster:This is something you can only, even if it's real, you can only detect across thousands of kids, not one kid. Yeah. And also, your kid's going to get some cavities, And you're not going to know whether it's gud's fluoride or not. So we're all kind of arguing in a sort of diffuse, ambiguous space. And that gives a lot of value to just, I don't know, stuff that lives in. What is living in your head more aggressively at the moment? And fear is more salient than reassurance. That's, yes. Yeah, this is driven by fear. It doesn't mean that there's nothing to worry about. But we do have to acknowledge that the studies are generally of poor quality.

1:04:30Emily Oster:and you shouldn't live your life based on fear of poor quality studies. And you should be happy that our kids are not dying of cholera and dysentery, which is a real possibility for kids all around the world just to bring it back to the other stuff we add to water. All right, Perry, fluoride in the water, smash or pass? I am a smash. I think the fluoride benefits people with the least access, which is generally what I'm for from a public health standpoint. And I think you should also read to your children. Emily, smash or pass? I'm a smash on fluoride. And I hope that we keep it in our municipal water supply.

1:05:13That's what I would like.

1:05:15Emily Oster:All right, Florida. We'll see what happens. That's it for fluoride. Your mailbag question of the week after the break. We all miss the 90s, the music, the shows, the outfits, and without a doubt, the snacks. Simple Mills is bringing back the golden age of snacking. They taste delicious like the snacks you grew up with, only they're made with real ingredients like watermelon seed flour, almonds, cashews, flaxseed, and organic coconut sugar. Fancy. You'll love the throwback taste of cheddar pop-ums, the nostalgic flavor of mini crunchy chocolate chip cookies and the familiar crunch of honey cinnamon sweet thins.

1:05:54Available in snack packs that are easy to toss into lunch boxes, backpacks, or your own bag. Simple Mills snack packs are simply the coolest.

1:06:02Emily Oster:Simple Mills. Throwback taste. Grown-up ingredients. I thought I looked so cute. I pieced together a cute outfit and this girl comes up to me, just sits next to me telling me, oh hey girl, I see your skin. I know what you're suffering with. I just remember feeling so just like distraught and like robbed of my time. When I finally freed myself of that conversation, the lights were coming on and the party was over. It felt like I had a sticker on my forehead that said, she has eczema. We've all been there, wanting to go out, feeling cute, forgetting about all your problems, and just existing in the present with joy.

1:06:45Emily Oster:But when you live with a visible skin condition, that can be a lot harder than it needs to be. This is Skin Queries. Listen on the iHeartRadio app, Apple Podcasts, or wherever you get the stories that make you feel understood. How's the new place? Get your Wi-Fi figured out? I got T-Mobile 5G home internet and I'm loving it. It's the fastest 5G home internet. My old provider was so slow. Mine is slow. And only 35 bucks a month. Do I need to try this? Try it for 15 days. Love it or get your money back. I love it already. There are over 250 reasons to join T-Mobile. Find yours and check availability at t-mobile.com slash home internet.

1:07:24Emily Oster:This is according to Oculus B test intelligence data second half of 2025 all rates reserved for T-Mobile. Guarantee within 30 days of cancellation. Hi Emily and Perry. This is Natasha from Massachusetts. My question came from your episode last week on gluten sensitivity and it's about MSG. A lot of older people in my life, especially ones I go to Chinese restaurants with, are convinced that MSG is responsible for headaches, brain fog, everything that's wrong in the world. I've even heard it called Chinese restaurant syndrome. Is this actually a real thing? MSG tastes so good. It would be such a bummer to cut it out if you don't have to.

1:08:03Emily Oster:Thanks so much. Emily, do you have MSG powder in your house? No, I do not. Do you? Is it next to your mac and cheese cheese that you use on everything? I have a lot of powders. It's in my spice rack. I'm a big fan of MSG. So before we answer the question of whether you can be allergic to MSG, I have to say the science here is fascinating. Um, MSG monosodium glutamate is a chemical that binds to certain receptors on your tongue. Uh, they're called T1, R1 and T1, R3, which are the specific umami taste receptors. So this, the umami flavor, uh, which is, um, that sort of like meaty, robust, uh, type of flavor comes from food that has glutamate in it.

1:09:00Emily Oster:It's an umptious flavor, absolutely. And whenever you taste something umami, like whether it's like mushrooms or things like that, it is the glutamate. It's not from monosodium glutamate, but it is glutamate binding to those receptors that gives you that flavor. So we all kind of like that flavor, truffles, like that kind of stuff. That's all glutamate. Monosodium glutamate, it's just a sodium attached to the glutamate and sodium is salt, you know. And so - So it's just like a salty umami deliciousness. It's just umami. As much as like sucrose is the sweet and citric acid is kind of a prototypical sour, monosomium glutamate is umami.

1:09:38Emily Oster:And it's quite delicious. But Emily, you tell me, can you be allergic? Or maybe I should say sensitive. There's really no evidence that people can be sensitive to this. And in fact, it would be surprising given that you also have sodium and you also have glutamate as you have outlined. And so the idea that together they would cause something that would be different from separate doesn't have a lot of mechanistic. I think people just eat too much from the restaurant and then they feel tired. Yes, 100%. This is a classic example of MSG being used in cooking. And there's a lot of other stuff that gets used in cooking.

1:10:22Emily Oster:You know, Chinese restaurants do. Asian cooking in general does add MSG sometimes as a spice, much like I do sometimes, just like adding salt or adding sugar or adding citric acid or whatever. But it is in all the other foods you eat, too, that have that bit of flavor profile. And, yeah, you just really can't be allergic to it. But there's a lot of salt and other stuff in that type of cooking, which can make you a little feel dehydrated and gross. And it's also really delicious. So you get full and sleepy and tired. Definitely. Yeah. It'll be a mistake. Don't blame the MSG, but just drink some extra water.

1:11:01All right. That's it for us today. Stick with us next week when we'll ask, what's the deal with ticks?

1:11:07Emily Oster:The bugs, not the Tourette's syndrome thing. With bugs. Ticks the bug. Wellness Actually is produced in association with iHeartMedia. Our senior producer is Tamar Abishai. Our executive producer at iHeart is Jennifer Bassett. Our theme music is by Eric Deutsch. And our content is for educational purposes only. If you like the show, help other people find us. Leave a rating and review on Apple Podcasts or your podcatcher of choice. And help us spread the word about the show. You can follow us on Instagram at wellnessactuallypod. And don't forget, we want to hear from you. Head over to wellnessactually.fm and leave us a question for our mailbag or suggest a topic for a future show.

1:11:49We'll let the influencers have the last word.

1:11:52Emily Oster:I'm going to expose some things about fluoride. Why have we been told we have fluoride in the drinking water? Prevent tooth decay. Prevent tooth decay. You were told that too, right? Yes. So was I.

1:12:17Emily Oster:We all miss the 90s. the music, the shows, the outfits, and without a doubt, the snacks. Simple Mills is bringing back the golden age of snacking. They taste delicious like the snacks you grew up with, only they're made with real ingredients like watermelon seed flour, almonds, cashews, flaxseed, and organic coconut sugar. Fancy. You'll love the throwback taste of cheddar pop-ums, the nostalgic flavor of mini crunchy chocolate chip cookies, and the familiar crunch of honey cinnamon sweet thins. Available in snack packs that are easy to toss into lunchboxes, backpacks, or your own bag. Simple Mills snack packs are simply the coolest.

1:12:56Emily Oster:Simple Mills. Throwback taste. Grown-up ingredients. I have been with Rasmussen University since 2013. All virtual. All of my professors throughout the entire journey have been nothing but supportive of making me reach my dreams. Rasmussen professors, they want to see you grow so that you can be what you went to school to be. I'm so thankful for Rasmussen University for being able to make it so easy and seamless. Rasmussen University. Find your seat and start now at rasmussen.edu. Across America, money is being abandoned. By taking a few seconds to check lift before your next ride, you can give money a better home inside your wallet.

1:13:41Emily Oster:Save the money. Check lift. This is an iHeart Podcast. Guaranteed Human.