Fluoride: Is Your Water Safe?

Summary

Science Vs: Fluoride – Is Your Water Safe?
Hosted by Wendy Zuckerman, Produced by Meryl Horne
Release Date: April 10, 2025

In this compelling episode of Science Vs, host Wendy Zuckerman delves into the contentious debate surrounding water fluoridation. Together with senior producer Meryl Horne, they navigate through the historical origins, celebrated benefits, and emerging controversies of adding fluoride to public water supplies. This summary captures the key discussions, insights, and conclusions drawn from interviews with experts and analysis of scientific studies.

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1. The Origins of Water Fluoridation

Meryl Horne sets the stage by recounting the historical detective story that led to the introduction of fluoride in drinking water:

[00:26] Meryl Horne: "There's so much controversy right now around water fluoridation."

The journey begins in 1901 with Frederick McKay, a young dentist in Colorado Springs, who notices an alarming pattern among his patients:

[00:49] Meryl Horne: "A lot of his patients have dark brown stains on their teeth. He writes that the color was sometimes dirty or an almost ebony black."

McKay's quest to uncover the cause of these stains leads him to suspect the local water supply. After decades of investigation, he identifies fluoride as the culprit responsible for both staining teeth and preventing cavities.

In 1945, Grand Rapids, Michigan, becomes the first U.S. city to add fluoride to its water, resulting in a 70% reduction in tooth decay among children:

[04:19] Wendy Zuckerman: "The children in Grand Rapids have less tooth decay than they did six years ago. It's working."

The Centers for Disease Control and Prevention (CDC) lauds water fluoridation as one of the greatest public health achievements of the century, alongside vaccines and tobacco control.

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2. Rising Controversy and Claims Against Fluoridation

Fast forward to 2025, and fluoride is no longer universally celebrated. Opposition has been growing, with notable figures like Robert F. Kennedy Jr., head of the Department of Health and Human Services, vocally declaring fluoride a poison:

[05:32] Meryl Horne: "Robert F. Kennedy, Jr. Who leads the Department of Health and Human Services, he thinks that fluoride is dangerous."

Critics argue that fluoride is a neurotoxin linked to a range of health issues:

[05:44] Wendy Zuckerman: "Fluoride, it's a neurotoxin, and it's found in rat poison."

Other alarming claims include:

• Lower IQ in children
• Increased risk of ADHD
• Brittle bones and higher hip fracture rates
• Increased risk of thyroid disease

Additionally, skeptics question the efficacy of fluoride in preventing cavities in the modern era of advanced dental care:

[06:02] Meryl Horne: "Water fluoridation, scientifically proven not to work."

These concerns have led some regions, including parts of Australia and Utah, to remove fluoride from their water supplies.

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3. Examining the Science: Neurodevelopmental Risks

The heart of the controversy lies in the potential neurodevelopmental risks associated with fluoride exposure, particularly during pregnancy. Meryl introduces Ashley Mallon, an epidemiologist from the University of Florida, who shares her journey from skepticism to concern after encountering studies suggesting a link between fluoride and lower IQ in children.

[10:24] Ashley Mallon: "We found that higher levels of fluoride in pregnant women's urine was associated with more neurobehavioral problems in their children by age three."

Mallon’s study, along with seven additional studies, predominantly found negative effects of prenatal fluoride exposure on children's brain development. However, two studies did not corroborate these findings, highlighting the inconsistent evidence.

Meryl emphasizes the complexity of isolating fluoride as the sole factor, given its presence in various sources like black tea, pesticides, and fluoridated toothpaste. Moreover, the lack of a clear biological mechanism linking fluoride to neurodevelopmental issues adds to the scientific uncertainty.

Noteworthy Points:

• Prenatal Exposure vs. Childhood Exposure: Most studies indicating risks focus on in utero exposure, whereas studies on postnatal exposure show mixed results.
• IQ Trends: Population-wide IQ scores have generally been increasing, complicating the narrative that fluoride significantly lowers IQ on a broad scale.
• Magnitude of Impact: Some researchers estimate that any IQ reduction due to fluoride is minimal (e.g., 2.5 points), questioning its practical significance.

Despite these findings, scientists remain divided, with many calling for more rigorous research to establish causality and understand underlying mechanisms.

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4. Community Impact: Calgary vs. Edmonton

To assess the real-world impact of fluoridation on dental health, the episode highlights Lindsey McLaren, a professor at the University of Calgary. Her research compares Calgary, which ceased fluoridation in 2011, with Edmonton, which continued to fluoridate its water.

McLaren’s study involved 5,000 second graders and revealed that:

• Calgary (No Fluoride): 65% of children had cavities in their baby teeth.
• Edmonton (Fluoridated): 55% of children had cavities.

This 10-percentage-point difference underscores the continued benefits of fluoride in preventing dental caries, particularly in vulnerable populations:

[32:32] Wendy Zuckerman: "Lindsey's study does seem to be, like, one of the best ones."

Furthermore, McLaren found that the removal of fluoride disproportionately widened the dental health gap between richer and poorer children, highlighting fluoride's role in reducing health disparities.

When Calgary revisited the issue, the community overwhelmingly voted to reinstate fluoride, with 62% in favor:

[34:12] Lindsey McLaren: "This was by far the largest majority in our history."

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5. Balancing Benefits and Risks

The debate hinges on weighing the proven dental benefits against the emerging and contested health risks. While fluoride’s role in reducing cavities, especially in children, is well-documented, concerns about its potential impact on brain development and thyroid function cannot be dismissed.

Key Considerations:

• Children's Oral Health: Fluoride remains a critical tool in preventing tooth decay, which can have long-term consequences for dental and overall health.
• Potential Neurotoxicity: Although some studies suggest risks, the evidence is not yet conclusive, and more comprehensive research is needed.
• Thyroid Health: Some studies indicate a possible association between fluoride and hypothyroidism, particularly in populations with iodine deficiency.
• Public Health Policy: Policymakers must consider both the benefits of dental health and the unknowns regarding neurological and endocrine health when making decisions about fluoridation.

Meryl and the experts interviewed in the episode express caution, advocating for continued research and transparent scientific dialogue to inform public health decisions.

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6. Expert Insights and Personal Perspectives

Throughout the episode, experts like Ashley Mallon and Lindsey McLaren provide nuanced views:

[35:39] Meryl Horne: "I just keep turning this over in my brain."

Meryl candidly shares her personal ambivalence, recognizing the validity of both sides of the argument. She acknowledges the significant benefits fluoride provides for dental health but remains concerned about the potential for unknown neurological effects.

[36:25] Meryl Horne: "I don't know. I am right there with him because, like, I can really see it from both sides."

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7. Conclusion: A Call for Further Research

The episode concludes with a clear message: the debate over water fluoridation remains unresolved due to mixed scientific findings and evolving public perceptions. Experts agree on the importance of ongoing research to fully understand fluoride's health implications.

[27:40] Lindsey McLaren: "Yes, at recommended optimal concentrations and keep the research going. So, so don't cut research funding."

Ultimately, Science Vs emphasizes the need for balanced, evidence-based decisions in public health, urging both policymakers and the public to stay informed as new research emerges.

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Notable Quotes with Timestamps

• Meryl Horne
  [00:42]: "It starts in 1901. So picture a young dentist, Frederick McKay, moves to Colorado Springs..."
  [13:18]: "It's really hard, right? Because in theory, like, you could try bottled water..."
  [36:21]: "I just keep turning this over in my brain."

• Wendy Zuckerman
  [04:19]: "Wow. That's big. That's in the biggies."
  [14:05]: "Wendy Zuckerman: Okay. It's intriguing. I'm not..."
  [31:02]: "Yeah, it's like, it's kind of hard to tell how much it matters."

• Ashley Mallon
  [10:51]: "I said, there's no way that something would be added to the drinking water that could potentially lower IQ."
  [14:17]: "We found that higher levels of fluoride in pregnant women's urine was associated with more neurobehavioral problems in their children by age three."

• Lindsey McLaren
  [31:24]: "So the prevalence of dental caries in Calgary kids in their baby teeth was about 65%."
  [34:12]: "This was by far the largest majority in our history."

---

Final Thoughts

"Fluoride: Is Your Water Safe?" presents a balanced exploration of a complex public health issue. While fluoride's dental benefits are clear, the potential neurodevelopmental and endocrine risks warrant further investigation. As communities continue to navigate this debate, the episode underscores the importance of ongoing scientific research and informed public discourse.

For listeners seeking a deeper understanding, the episode provides 105 citations available in the show notes, encouraging audiences to explore the extensive research backing the discussions.

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Listen to Science Vs for more insightful explorations of science vs. myth on pressing contemporary issues.

Transcript

[Wendy Zuckerman]

Hi, I'm Wendy Zuckerman, and you're listening to Science versus Today. On the show, we are pitting facts against fluoride. Should we put it in the water? To tell us all about it, senior producer Meryl Horne. Hello.

[Meryl Horne]

Hi. Okay. There's so much controversy right now around water fluoridation.

[Wendy Zuckerman]

I know.

[Meryl Horne]

Which we'll get to.

[Wendy Zuckerman]

Okay.

[Meryl Horne]

But first, I have to tell you the, like, wild and surprising story about why we started putting fluoride in the water in the first place. Because it is kind of weird that we do this, right? I guess.

[Wendy Zuckerman]

So how did it all start?

[Meryl Horne]

Well, it's actually a detective story.

[Wendy Zuckerman]

Ooh.

[Meryl Horne]

It starts in 1901. So picture a young dentist, Frederick McKay, moves to Colorado Springs, and he starts seeing patients and immediately notices that there's something weird going on. A lot of his patients have dark brown stains on their teeth. He writes that the color was sometimes dirty or an almost ebony black.

[Wendy Zuckerman]

Mm.

[Meryl Horne]

Do you wanna see pictures?

[Wendy Zuckerman]

Of course I do.

[Meryl Horne]

All right.

[Wendy Zuckerman]

Oh, it's a real black line, thick line across their teeth. That is unsightly.

[Meryl Horne]

Yeah. So McKay starts to obsess over this, searching for an explanation. He writes to a friend at one point who responded, quote, I have never seen a stain that penetrated the enamel so deeply before. And this guy guessed that maybe the stains came from dead organisms. So, like, they had no idea at first, like, what was going on here.

[Wendy Zuckerman]

I mean, you could say it looks like mold on their teeth. I can understand why they went for the dead organisms.

[Meryl Horne]

Yeah. It must have been pretty startling, right?

[Wendy Zuckerman]

Yes.

[Meryl Horne]

So McKay starts traveling around the US looking at other places which also have this staining, and he starts suspecting that it's coming from, quote, something in the drinking water, but he doesn't really know for sure. But then he goes to this town in Arkansas where people only started getting stains in their teeth if they were born after 1909. And apparently that's when the town switched water supplies. So now they just have to see what is in the new water supply.

[Wendy Zuckerman]

Yes. What's different?

[Meryl Horne]

And so someone does this analysis, and McKay finally gets an answer after three decades of searching. It was the fluoride.

[Wendy Zuckerman]

Right. This new water in Arkansas had higher fluoride levels.

[Meryl Horne]

Yeah. Yeah. It had really high fluoride in that water. They weren't adding it, but these places just happened to naturally have a lot of fluoride seeping into the water from the earth's crust. And now we know that when you drink water with high levels of fluoride, it can mess with the crystal structure of your teeth, and that can lead to staining.

[Wendy Zuckerman]

Right.

[Meryl Horne]

But then McKay also noticed something else that was weird about these people with the stained teeth. They basically weren't getting cavities. So, like, even though the fluoride was turning teeth brown, it was also, like, protecting them.

[Wendy Zuckerman]

That's cool. What a Dr. Jekyll, Mr. Hyde moment.

[Meryl Horne]

Yeah. And so they figured, like, okay, what if we could, like, add fluoride to the water in places that don't already have it, like, just a little bit, so that we can get this, like, protection from cavities, but not so much that it turns the teeth brown.

[Wendy Zuckerman]

So this was the beginning.

[Meryl Horne]

Yeah. This is, like, the birth story of water fluoridation. So in 1945, Grand Rapids, Michigan, was the first city in the US to add fluoride to the water. And people were really excited. The government released a PSA about it.

[Wendy Zuckerman]

The children in Grand Rapids have less tooth decay than they did six years ago. It's working.

[Meryl Horne]

Yeah. They found that it slashed rates of tooth decay by as much as 70%.

[Wendy Zuckerman]

Wow. Now our children can have better health through fluoridated water. They can drink away tomorrow's tooth decay.

[Meryl Horne]

And after that, we started fluoridating water in most of the U.S. australia, Ireland, and a lot of places in Brazil and Canada. And the CDC lists this as one of our greatest public health achievements of the past century, along with vaccines and figuring out that tobacco is bad.

[Wendy Zuckerman]

Yeah. Wow, that's big. That's. That's in the biggies. But then Fast forward to 2025, and people are not excited about drinking away tomorrow's tooth decay.

[Meryl Horne]

Well, there's actually been some opposition to this from the start, but recently, things are really heating up, even at, like, the highest levels. So Robert F. Kennedy, Jr. Who leads the Department of Health and Human Services, he thinks that fluoride is dangerous.

[Wendy Zuckerman]

I think fluoride is a poison.

[Meryl Horne]

But he's not alone. There's a whole kind of chorus of people saying that adding fluoride to the water has been a huge mistake, because fluoride is actually really bad for us.

[Wendy Zuckerman]

Fluoride, it's a neurotoxin, and it's found in rat poison.

[Meryl Horne]

It literally drops IQ in children. It helps cause adhd. It makes our bones brittle and increases hip fractures.

[Wendy Zuckerman]

Fluoride in drinking water absolutely increases the risk of thyroid disease.

[Meryl Horne]

And on top of all the, like, dangers of fluoride, people are also saying now that it doesn't even work to prevent cavities anymore, now that we have, like, better dental Care not only ineffectual, but harmful because of all the science that's emerging. Water fluoridation, scientifically proven not to work.

[Wendy Zuckerman]

Is fluoride really the hero that we.

[Meryl Horne]

Once thought it was? And so now fluoride is being taken out of the water in some places in Australia and now Utah in the.

[Wendy Zuckerman]

U.S. so who's right? Is fluoride the hero that we thought it was, or is it the nemesis that people now say it is?

[Meryl Horne]

Yeah, that's the question. And just to say that the research on this was not at all what I was expecting it to be.

[Wendy Zuckerman]

All right. The science of fluoride is covered up just after the break. This episode of Science Versus is presented by Amazon. The last thing you want to do when you're sick is go to the pharmacy to pick up a prescription, because then you're standing in a long line with a whole bunch of sick people and everyone is sick of being sick around other people who are sick. Amazon Pharmacy will deliver right to you fast. So you can get meds without congregating amongst the contagious. Healthcare just got less painful. Amazon Pharmacy PayPal lets you pay all.

[Meryl Horne]

Your pals like your dinner dates. How are we splitting the bill?

[Wendy Zuckerman]

Um, evenly.

[Lindsey McLaren]

Well, I only got soup.

[Meryl Horne]

Let's Split it on PayPal based on what people ate.

[Wendy Zuckerman]

Get started in the PayPal app, a PayPal account is required to send and receive money. Welcome back. Today we're looking at whether fluoride should be in our water or not. Is it safe or not? Meryl Hawn, Ph.D. is here with us.

[Meryl Horne]

Hi, Wendy.

[Wendy Zuckerman]

Meryl, where do we begin? Is fluoride a poison now?

[Meryl Horne]

Well, I mean, like a lot of stuff at really high levels, fluoride can kill you. So the most dramatic example that I found of this was in the 90s, there was a town in Alaska that accidentally dumped like way too much fluoride into the water supply. And like dozens of people got really sick. Someone even died. The case study said that quote, After 24 hours of intractable vomiting, a 41 year old man was found dead at home.

[Wendy Zuckerman]

Oh, God. How much fluoride did they dump in, in the water?

[Meryl Horne]

In that case, it was way more than we normally put in. So, like, that water that that guy drank had roughly like 350 times more than what we aim for when we fluoridate water.

[Wendy Zuckerman]

Wow. Right?

[Meryl Horne]

And at really high levels, it can stop your heart.

[Wendy Zuckerman]

Okay, Right. But there's, there's a lot of things that if you have too much of them, can kill you, including water that is not fluoridated. The question obviously becomes, are the levels of fluoride that we're putting in the water safe?

[Meryl Horne]

Yeah, that's the thing that everybody's fighting about with, you know, some people saying that it's not safe, some people saying that it is. But there is one downside that kind of everyone agrees is happening even at these low levels of fluoride that we're putting in the water. And that's the thing that we mentioned at the top of the show, where fluoride can stain your teeth, and that can happen even at lower levels, too. And at that case, it's not like the photos that I showed you of, like, these brown teeth. It's just kind of like a whitish stain. But, like, 10 years ago, we checked to see how many kids in the US have this, and it was 70%. And so the government took that seriously enough that they changed the recommendation for how much fluoride should go into the water. It was lowered 10 years ago.

[Wendy Zuckerman]

Okay, what about the big thing I hear about now, and I've seen headlines saying this and that and the other is around fluoride affecting our brains, some saying it's damaging, others saying it's not. What's going on here?

[Meryl Horne]

Yeah, let's dive into that one, since people are really worried about that. And it's also where a lot of the research has been. So to walk us through this, I called up epidemiologist Ashley Mallon, an assistant professor at the University of Florida.

[Wendy Zuckerman]

Florida. Got it.

[Meryl Horne]

Yep. So Ashley first remembers when she heard about this idea that fluoride might be bad for us. She was with a family member.

[Ashley Mallon]

I was drinking a bottled water, and they said, don't drink that. There's fluoride in it. And I said, yeah, well, it's good for my teeth. And they said, no, fluoride lowers iq. And I said, there's no way that something would be added to the drinking water that could potentially lower iq.

[Meryl Horne]

And what about it felt kind of implausible?

[Ashley Mallon]

Yeah, I was skeptical because this is a widely used public health intervention that's supposed to be protecting our teeth, and it's supposed to be something that's good for us. So I just said they wouldn't add that to the drinking water if it was harmful in any way. Like, I couldn't even fathom that that was a possibility.

[Wendy Zuckerman]

Mm. Yeah. I hate that.

[Meryl Horne]

But, like, she was intrigued enough that Ashley started looking into the research. And at the time, there was a little bit there. Like, there was a study in the 90s that looked at over 500 rats and found that giving them fluoride could change their behavior. Like it made some of them hyperactive. And then she also found some studies in people like in China. There are a lot of places with these really high levels of fluoride in the water naturally. Yeah. And some of those studies had been finding that people who lived in these areas had lower IQs.

[Wendy Zuckerman]

So at high doses. Yes. But the question is, what about the low doses?

[Meryl Horne]

Yeah. So that's what Ashley started looking into herself.

[Ashley Mallon]

But there were no studies on lower exposures. Really, at that time, I was like, huh.

[Meryl Horne]

And so she decided to do her own research on this. She wanted to find out if being exposed to fluoride in the womb could affect brain development.

[Wendy Zuckerman]

Mm.

[Meryl Horne]

So she got involved in this big study in California. Here's how it worked. So they started following a couple hundred pregnant people, and they were taking pee samples from them. And this way they could look at how much fluoride was in their pee.

[Wendy Zuckerman]

Okay.

[Meryl Horne]

And that kind of roughly maps out to how much fluoride you're taking in. But by the way, this isn't just looking at like, fluoride from the water. Cause we actually do get fluoride from a bunch of different sources. Something like 60% of it comes from the water, but we also get it from, you know, stuff like black tea apparently has a lot of fluoride in it. Pesticides can have it, or if we swallow little bits of fluoridated toothpaste. So, yeah, the researchers here are looking at kind of like overall fluoride exposure.

[Wendy Zuckerman]

Okay.

[Meryl Horne]

And then they. They followed up with these moms three years later. So by now their kids are three, and they had them fill out a survey about their kids where they asked them about all sorts of stuff.

[Ashley Mallon]

It'll ask symptoms of autism, anxiety, depression, attention deficit hyperactivity disorder, physical symptoms. So stomach aches, headaches, temper tantrums.

[Meryl Horne]

Like people will say, like, oh, my kid has temper tantrums all the time. Or like, oh, that's really rare. Like that kind of a thing.

[Ashley Mallon]

Yeah. So it's rated from 0 to 2. And it'll capture whether the behavior is either typical or kind of over and above what would be considered typical for that developmental stage.

[Wendy Zuckerman]

Okay.

[Meryl Horne]

So yeah, they're like casting a wide net here to see if people who had more fluoride in their bodies when they were pregnant went on to have kids with more of any kind of like, neural behavioral issue when they were three.

[Wendy Zuckerman]

Uh huh. And so what did they find?

[Meryl Horne]

So Ashley was working from home, looking at her data on her laptop, when she saw the results.

[Ashley Mallon]

I'm like, oh, my gosh. Someone. I want someone to check this to make sure this is real. Yeah.

[Meryl Horne]

Cause what did you see?

[Ashley Mallon]

We found that higher levels of fluoride in pregnant women's urine was associated with more neurobehavioral problems in their children by age three.

[Wendy Zuckerman]

Mm. What kinds of problems?

[Meryl Horne]

They did have more temper tantrums. They had more anxiety and symptoms linked to autism.

[Wendy Zuckerman]

Uh huh. And can you put some numbers around this? I mean, when you say more tantrums, more anxiety, I mean, by how much?

[Meryl Horne]

Well, it wasn't like, you know, every kid who had some fluoride in the water got anxiety.

[Wendy Zuckerman]

Right.

[Meryl Horne]

But what she did is she kind of took the kids who were kind of near the bottom end of getting exposed to fluoride and compared them to the kids who are more towards the higher end of fluoride exposure. And here's what she saw.

[Ashley Mallon]

Their children had nearly double the odds of exhibiting the clinically relevant neurobehavioral problems by age three.

[Meryl Horne]

Whoa, double the odds?

[Ashley Mallon]

Nearly double? It was almost double. Yeah.

[Wendy Zuckerman]

Okay. It's intriguing. I'm not. It's not a huge study. 200 people. Um, yeah.

[Meryl Horne]

It's funny, I thought that you would be way more, like, surprised and alarmed at this study. Like, that's how I felt when I. When I saw this. There was like a turning point for me where I was like, what? Like fluoride might actually be doing something bad here.

[Wendy Zuckerman]

Yeah. I guess if I'm going to be honest about my biases here, I sort of wear. Ashley was before she did the study and she was drinking the water and her family member said, this causes brain damage. And she's like, absolutely not. And because I know the scientific status quo for so long has said, no, it's safe. So I can see myself looking for holes in this paper. It's not a randomized controlled trial, so we can't say that the fluoride caused these differences. There might have been other differences between the groups. So I. But what do other studies show here?

[Meryl Horne]

Okay, so I found eight studies altogether that basically did what Ashley did. So they looked at prenatal fluoride exposure.

[Wendy Zuckerman]

Right. Look. Pregnant women following pregnant women. Yeah, yeah, yeah. And looking at places with like, not huge amounts of fluoride in the water, but kind of relatively low levels. The amount you'd find in a city in Australia or the US that fluoridates their water.

[Meryl Horne]

Yeah, yeah. And then they followed their kids and looked for behavioral issues or sometimes lower iq. So okay, so out of those eight studies, Right. Six of them found bad stuff and two of them didn't find anything bad. So six out of eight studies did find some sort of like negative effect on the brain from prenatal exposure to fluoride.

[Wendy Zuckerman]

Yeah. Huh.

[Meryl Horne]

But the thing is, that's all just one group of studies. So other scientists tackle this in a completely different way and they'll zoom in on water fluoridation specifically and ask if you grew up with fluoridated water, do you have a lower IQ later in life?

[Wendy Zuckerman]

Mm. Right.

[Meryl Horne]

And a lot of those studies don't find any differences.

[Wendy Zuckerman]

Oh, that's so confusing. Suggesting what? That in Ashley's studies, in those prenatal studies, it's not from drinking the water that's the problem, but from swallowing toothpaste.

[Meryl Horne]

I mean, it could be these other sources. Yeah, it could be like that. Maybe it's not the fluoride in the water. It could be they're all drinking a lot of black tea or something. It could also be the difference in when the kids are getting exposed. Because a lot of the studies finding effects, they're looking at kids who are exposed in utero and they're fetuses and a lot of the ones that aren't are looking after they were born. Another thing that we haven't talked about yet here is that we don't really know what the mechanism would be yet. Like, there are some ideas, but the researchers aren't really like coalescing around one thing that is happening.

[Wendy Zuckerman]

Okay, interesting. I mean, it's because it's such a huge call to say so basically that in all of the places that have added fluoride to the water in the us, Australia, Canada, Ireland, is there any evidence that on a population wide level that those populations are dumber than places that have not fluoridated the water?

[Meryl Horne]

No. And in general, IQs have been going up, like in places like the U.S.

[Wendy Zuckerman]

Hard to say that now, but.

[Meryl Horne]

And like even one researcher who thinks that there is something here estimated that the difference between like growing up in a community with fluoridated water and not is only the difference of like two and a half IQ points. So that feels like not that big a deal.

[Wendy Zuckerman]

And so where are you at with this now?

[Meryl Horne]

Well, I live in New York City and we do have fluoridated water here.

[Wendy Zuckerman]

Right.

[Meryl Horne]

But like I haven't stopped drinking it. Like I'm not worried about it for my brain or my kids brains. Like I just don't think the evidence is there yet. But I do think that if I were pregnant, like, if I had known all this when I was pregnant, then I would have avoided drinking fluoridated water then.

[Wendy Zuckerman]

Really?

[Meryl Horne]

I don't know. I've talked to enough researchers on this pregnancy thing specifically, that say, you know, they would not do it. They would not drink fluoridated water. That. It freaks me out now. Yeah.

[Wendy Zuckerman]

So then what are you supposed to do if you're pregnant? Get a new water supply.

[Meryl Horne]

I mean, it's really hard, right? Because in theory, like, you could try bottled water, but we don't actually know a lot of the time how much fluoride is in bottled water. Some of it might have fluoride in it, too.

[Wendy Zuckerman]

Yeah. And then you got to worry about the bloody microplastics with the hormone disruptors that we talked about last season.

[Meryl Horne]

I know. Like, I think it's not perfect, but, like, I would. Would probably look into a filter. There's some filters that get fluoride out of the water. Or honestly, if it was just for a limited period of time, like, if I were pregnant, maybe I would just buy distilled water that didn't have any fluoride in it and, like, try to drink that. But, like, this is all probably being super cautious since tons of kids are exposed to fluoride in the uterus and don't have these behavioral issues, and there are just still some big unknowns.

[Wendy Zuckerman]

Okay, so where we're at with the brain stuff and fluoride is that there is some emerging evidence that if you're pregnant, this could be doing something to the fetus. The science is still unclear, but based on where it's at, you think it's worth thinking about?

[Meryl Horne]

Yeah.

[Wendy Zuckerman]

For us big kids come out of the vagina making podcasts. Is there other stuff that we need to worry about?

[Meryl Horne]

Well, it's not just about the brain here. Like, some people are worrying that fluoride might be making our bones weaker or increasing our risk of thyroid disease. Like hypothyroidism.

[Wendy Zuckerman]

Yeah.

[Meryl Horne]

And there is some evidence that that stuff is real, too, even at relatively low levels.

[Wendy Zuckerman]

Really?

[Meryl Horne]

Yeah. Yeah. So, like, for. For the thyroid, like, we know that the thyroid needs iodine. Right. If you don't get enough iodine, then you can get a goiter. So fluoride can sort of outcompete iodine. So in the past, we've actually given fluoride as a treatment for people who have overactive thyroids. And there was a study that found that people who lived in an area with fluoridated water were twice as likely to have hypothyroidism than people who didn't. But like, other studies haven't found those associations, or like Juan found that it was only significant if you also had an iodine deficiency to begin with.

[Wendy Zuckerman]

So what do we make of that as well? What do you make of it?

[Meryl Horne]

Yeah, I mean, it's not like I looked at the evidence and was like, oh, this is real for sure. Like fluoride is giving us all hypothyroidism. And then for other stuff it's even less convincing. Like for bone health. There were some studies that say that drinking fluoridated water can increase your risk for bone fractures. But there was a meta analysis that looked at everything together and said that there was no increased risk.

[Wendy Zuckerman]

Uh huh. Reassuring.

[Meryl Horne]

But then like, I don't know, for me, even if there are just a few studies saying that some of these risks could be real, it doesn't make me feel great because, like, I mean, the stakes are so high. We're doing this at such a big scale that ideally you'd want to see like a mountain of rock solid evidence of studies all saying this is totally safe. Like this is okay to be basically forcing this many people to be having this chemical.

[Wendy Zuckerman]

Right.

[Meryl Horne]

And we don't have that. I talked to Ashley about why we don't have a more definitive consensus on this. I mean, why, why has it taken so long? Is this kind of a failure of science?

[Ashley Mallon]

I think a big part of it is that it wasn't acceptable to ask these questions up until recently. To even ask the question, you'd be considered a tinfoil hat wearing conspiracy theorist probably up until 10 years.

[Meryl Horne]

Wow, that recent?

[Ashley Mallon]

Yeah.

[Wendy Zuckerman]

All right, well, this episode has taken quite the turn.

[Meryl Horne]

Yeah.

[Wendy Zuckerman]

I mean, clearly fluoride is not the devil or poison, as some people are claiming at the levels we put in our water. But it really is frustrating that we don't have more science on this. And the science that we have is muddy. I guess that's why you see these big fights online with people some saying it's safe, some saying it's not, because you really can cherry pick the data on all these fronts. You can pick your it's bad for the thyroid study and you can pick it's bad for the brain study or, or you can pick a study that's saying the opposite, I guess. But what it does tell us though, the fact that for, for a lot of this stuff it is muddy and that you do see, studies showing both sides tells us that whatever fluoride is doing in the water, it's not super dramatic because then you would see the same results in, you know, basically all studies.

[Meryl Horne]

Yeah, that seems true.

[Wendy Zuckerman]

Okay, so we've talked a lot about the potential risks. Now we need to talk about the potential benefits. The reason that we have been doing this in the first place is to protect our teeth. So is fluoride still doing that?

[Meryl Horne]

That's after the break.

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[Wendy Zuckerman]

Welcome back. Today, we're talking about fluoride. Maryl, any benefits to putting it in the water?

[Meryl Horne]

Well, scientists all agree that back in the 1940s, when we first started doing this, there was this huge benefit. But lots of people today are saying that things are different now. And, like, I think it. It does kind of make sense because when we first started doing this, our teeth were way worse. Like, we didn't go to the dentist as often. We didn't get sealants or brush our teeth with fluoridated toothpaste.

[Wendy Zuckerman]

Right?

[Meryl Horne]

So something like putting fluoride in the water had this big potential to make a huge difference. Cause our teeth were so crappy, right? Where now people say that, like, well, we don't really need to be doing that anymore because we have all these other, like, you know, tool in the toolbox to help our teeth.

[Wendy Zuckerman]

So are they right? I mean, does adding fluoride to the water, is it still preventing cavities or not?

[Meryl Horne]

Well, now we actually have, like, kind of a perfect opportunity to look at this, because as cities are taking fluoride out of the water today, we can see, like, okay, how much, like, do the teeth actually get worse in places that do that?

[Wendy Zuckerman]

Right.

[Meryl Horne]

And so that's what I wanted to talk about with Lindsey McLaren. She's a professor in community Health sciences at the University of Calgary in Canada. And this all first got on her radar back in 2011 when her city decided to stop putting fluoride in the water.

[Lindsey McLaren]

When it. When that all came out, I just. It was just fascinating to me, like, oh, we're not going to have fluoride in the water anymore. Isn't that interesting?

[Meryl Horne]

And Lindsay and some of her public health, like, nerd friends saw this and they published an op ed in the local paper, just kind of questioning whether this was actually a good idea.

[Lindsey McLaren]

And like, the hate mail came instantly. Like, we got hate mail immediately saying what? Yeah, oh, just like, you know, you guys are liars and you know you're fraudulent. And I was like, oh, okay, this is very interesting.

[Meryl Horne]

You're like, let's dive deeper into this field where I'm getting hate mail.

[Lindsey McLaren]

Well, exactly, exactly. Because I actually. And I feel like this is something where I was kind of misunderstood. Like, I was actually genuinely open to some of the comments I was receiving.

[Meryl Horne]

So Lindsey was like, yeah, let's do some science here. Like, we're taking fluoride out of the water. Will our teeth get crappier?

[Wendy Zuckerman]

Yeah.

[Meryl Horne]

And I wanted to talk to her about this one study that she did looking at cavities in kids. They did this one about seven years after the city stopped water fluoridation. And so they looked at kids who had basically gone their entire lives without fluoride in the water. So these kids were about 7 years old and they, they started by sending out teams of dental hygienists and researchers to schools in Calgary to check their teeth.

[Lindsey McLaren]

So they were just all over the city, you know, for an entire year.

[Meryl Horne]

They would like set up shop in the nurse's office, usually where dental hygienists would look at each kid's mouth one by one for signs of tooth decay. And Lindsay's team wanted to make sure that the kids felt comfortable with this.

[Lindsey McLaren]

In fact, the kids seem to find it kind of fun. And like, we'd have sort of groups of five kids come in at a time and be on deck and like, they'd be dancing around and like, they thought it was fun because they got pulled out of class. And because of the dental light, we had sunglasses for them and they loved the sunglasses. Like, they were just walking around like they were so cool.

[Meryl Horne]

It's like a dance party.

[Lindsey McLaren]

Yeah, yeah, it was really cute.

[Meryl Horne]

And they weren't just looking at these kids in Calgary that had lost fluoride from their water. They were also doing this entire thing in another city that was nearby called Edmonton that kept fluoridating their water.

[Wendy Zuckerman]

Listen, what did they find? You're stringing me along like floss here.

[Meryl Horne]

Okay, okay. So, yeah, we've got 5,000 second graders across these two cities and now they can Finally See, did the kids who grow up with fluoride added to the water have cavities compared to the kids in Calgary?

[Wendy Zuckerman]

Yes. So what did they say?

[Lindsey McLaren]

So the prevalence of dental caries in Calgary kids in their baby teeth was about 65%.

[Wendy Zuckerman]

Fluoride no longer in the water. 65% had cavities. All right, drumroll. What is it? When fluoride is in the water, that.

[Lindsey McLaren]

Was compared to about 55% in Edmonton.

[Meryl Horne]

It's like 10 percentage points different. Yeah.

[Wendy Zuckerman]

Yeah.

[Lindsey McLaren]

So that's the percent of kids that have any cavities at all.

[Meryl Horne]

What did you think when you saw that data?

[Lindsey McLaren]

This was larger than I expected.

[Wendy Zuckerman]

Okay. And what about other studies?

[Meryl Horne]

So other studies generally find the same thing. Kids do tend to get more cavities when they grow up without fluoridated water.

[Wendy Zuckerman]

Okay, okay. So one thing that we've been told about fluoride. Still true, still good for our teeth. Yeah.

[Meryl Horne]

These kids are getting fewer cavities. And I know maybe you're thinking, who cares? The little cavity here or there, maybe it doesn't matter so much.

[Wendy Zuckerman]

Right. It's just their baby teeth. They're gonna get more.

[Meryl Horne]

Well, it actually does matter. So, like, if you lose your baby teeth early, like, if you have to get them extracted, then your adult teeth might not come in as straight. So that could affect you for the rest of your life. And we do have evidence that living in a place with less fluoride in the water will make it more likely that kids will need to get teeth extracted and also get intense dental work done. Like, where they'll need to go under general anesthesia, which ideally, like, we'd want to avoid putting kids through that.

[Wendy Zuckerman]

Yeah.

[Meryl Horne]

And we also have evidence that fluoride is particularly good for kids who come from poorer families. Like in Lindsey's study, after Calgary stopped fluoridating their water, it widened the gap between the richer and the poorer kids when it came to, like, how bad their teeth were. Not all studies find this to be true, but Lindsay's does seem to be, like, one of the best ones.

[Wendy Zuckerman]

And so what about adults? Does it matter for us?

[Meryl Horne]

Well, it's like, it's kind of hard to tell how much it matters. Like, if you're already an adult and you live in a place with fluoridated water, how much that makes a difference? Like, one study said that there was just 2% less tooth decay for adults who lived in places with more fluoride in the water.

[Wendy Zuckerman]

Oh, it's tiny. Is that because we're better at Brushing our teeth than kids?

[Meryl Horne]

Partly, yeah, actually. And also apparently I just learned this, that the enamel of baby teeth is thinner and more porous. And then even after you start getting your adult teeth, those teeth are also more cavity prone. Since they're softer, it takes them years for them to reach maximal hardness, according to one paper.

[Wendy Zuckerman]

Wow. Maximal hardness.

[Meryl Horne]

Yeah.

[Wendy Zuckerman]

That's an odd way to describe anything to do with children.

[Meryl Horne]

So, yeah, it's, like, pretty convincing to me that fluoride in the water is still helping our teeth. Which brings us back to Lindsey's study. So there's one more thing I wanted to tell you about that, which is about how people reacted to it in Calgary. So after her studies came out, the town actually ended up voting on this and decided to put fluoride back in the water. Whoa.

[Wendy Zuckerman]

They listened to the teeth science? They cared about their teeth.

[Meryl Horne]

Yeah, it seems like it. Like, they had a vote. And 62% of the people said, yes, we want to fluoridate our water again.

[Lindsey McLaren]

And this was by far the largest majority in our history. It was in the past. It's been more like, you know, 49, 51 type of.

[Wendy Zuckerman]

Type of thing. Oh, wow.

[Lindsey McLaren]

Yeah, so this was quite a strong sign of support.

[Meryl Horne]

Yeah. So her study got a lot of attention, like, even in the US here's some of that coverage.

[Advertisement Voice]

In Calgary, there was life before fluoride was removed from drinking water and life.

[Wendy Zuckerman]

After children, mostly children, had to suffer so badly.

[Meryl Horne]

So, yeah, I asked Lindsay, like, where she. She lands after all this. Should we be putting fluoride in the water?

[Lindsey McLaren]

Yes, at recommended optimal concentrations and keep the research going. So. So don't cut research funding. That seems like a pertinent thing to say right now.

[Wendy Zuckerman]

Sure does. Sure does. All right, well, but Lindsay's looking at the teeth. Was she also thinking about all of the other potential risks around brain development and thyroid stuff when she answered that question?

[Meryl Horne]

Yeah, we talked about that research like it's something she's keeping an eye on, but so far it hasn't changed her mind on water fluoridation in general.

[Wendy Zuckerman]

Hmm, messy. I mean, zooming out here, you did speak to a lot of scientists in this space. What are they telling you when they put the risks and the benefits together here, where do they stand?

[Meryl Horne]

I mean, they were really split. Actually, I was surprised by how many scientists, including some dentists who told me they think we should either stop or they were, like, seriously doubting it. Like, there is one that I talked to who used to be a big fluoride supporter, and he'd been thinking more and more about this research. And I asked him, like, all right, like, if you're in charge of the machine, do you cut it off?

[Wendy Zuckerman]

Yeah.

[Meryl Horne]

And he just, like, paused for 20 seconds in silence while he, like, tried to figure out what to say. And then he just said, like, sorry, I can't give you an answer. We need more research. Which is kind of where I'm at. Like, I just. I keep turning this over in my brain.

[Wendy Zuckerman]

I was just so, Meryl, do you think we should keep florading the water?

[Meryl Horne]

I don't know. I am right there with him because, like, I can really see it from both sides. I think what's so hard about it for me is that. But I'm pretty convinced that the benefit to the teeth is real. But it's like, at the end of the day, it's still just the teeth, where even if the science on the brain damage isn't as convincing, the stakes are so much higher that if the effect is real, we need to stop fluoridation, even if it is good for the teeth. Obviously, we can't be giving people something that might be damaging their brains.

[Wendy Zuckerman]

Right? Right.

[Meryl Horne]

What do you think?

[Wendy Zuckerman]

That's science versus, hey, 20 seconds of silence. Is that about it? Okay. So, Meryl, how many citations are in this episode?

[Meryl Horne]

We had a lot. 105 citations.

[Wendy Zuckerman]

Whoa, 105. Wow. So before you sent us angry, angry emails, Instagram messages, please have a look at our transcript. How could people find these 105 citations?

[Meryl Horne]

Yeah, you can go to the show notes and then follow the links to the transcripts. But you can also send the angry emails if you want. You know, we don't mind.

[Wendy Zuckerman]

It's true. On Instagram, we are ScienceVS. My TikTok is Wendy Zuckerman. Come say hello. Let us know what you thought of the episode. All right. Thanks, Meryl.

[Meryl Horne]

Thanks, Wendy.

[Wendy Zuckerman]

This episode was produced by Meryl Horn with help from me, Wendy Zuckerman, Rose Rimler, Michelle Dang and Aketty Foster. Keys we're edited by Blythe Terrell Mix and sound design by Bobby Lord. Fact checking by Erica Akiko Howard. Music written by Bumi Hidaka, Peter Leonard, Emma Munger, so Wiley and Bobby Lord. Thanks to all of the researchers that we spoke to for this episode, including Professor Christine Till, Professor Jonathan Broadbent, Dr. John Morris, Professor Bruce Lanphear, Professor Loch Doe, Dr. Maria Kipper, Professor Philippe Hajul, Professor Stephen Peckham, Dr. Tommaso Filippini, and Professor Steven Levy. Besides, Versus is a Spotify Studios original listen to us for free on Spotify or wherever you get your podcasts. And if you are listening on Spotify, follow us and tap the bell icon so that you get notifications when new episodes come out. I'm Wendy Zuckerman. Back to you next time.