Meryl Horn (Senior Producer, PhD)
Appearances
Science Vs
The Real Anti-inflammatory Diet
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Science Vs
The Real Anti-inflammatory Diet
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Science Vs
Fluoride: Is Your Water Safe?
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, 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.
Science Vs
Fluoride: Is Your Water Safe?
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? Right. And a lot of those studies don't find any differences.
Science Vs
Fluoride: Is Your Water Safe?
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.
Science Vs
Fluoride: Is Your Water Safe?
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 their 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. There are some ideas, but...
Science Vs
Fluoride: Is Your Water Safe?
Researchers aren't really like coalescing around one thing that is happening.
Science Vs
Fluoride: Is Your Water Safe?
And even one researcher who thinks that there is something here estimated that the difference between growing up in a community with fluoridated water and not is only the difference of two and a half IQ points. So that feels like not that big a deal.
Science Vs
Fluoride: Is Your Water Safe?
Well, I live in New York City and we do have fluoridated water here. Right. 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. Really?
Science Vs
Fluoride: Is Your Water Safe?
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. It freaks me out now, yeah.
Science Vs
Fluoride: Is Your Water Safe?
I mean, it looks, you could see, it looks like mold on their teeth.
Science Vs
Fluoride: Is Your Water Safe?
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.
Science Vs
Fluoride: Is Your Water Safe?
Like, I think... It's not perfect, but like I 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.
Science Vs
Fluoride: Is Your Water Safe?
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.
Science Vs
Fluoride: Is Your Water Safe?
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. Yeah. And there is some evidence that that stuff is real, too, even at relatively low levels.
Science Vs
Fluoride: Is Your Water Safe?
Yeah. It must have been pretty startling, right? Yes. So, McKay starts traveling around the U.S. 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.
Science Vs
Fluoride: Is Your Water Safe?
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.
Science Vs
Fluoride: Is Your Water Safe?
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.
Science Vs
Fluoride: Is Your Water Safe?
But like other studies haven't found those associations or like one found that it was only significant if you also had an iodine deficiency to begin with. So what do we make of that as well? What do you make of it? 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.
Science Vs
Fluoride: Is Your Water Safe?
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.
Science Vs
Fluoride: Is Your Water Safe?
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. For sure.
Science Vs
Fluoride: Is Your Water Safe?
This is okay to be basically forcing this many people to be having this chemical.
Science Vs
Fluoride: Is Your Water Safe?
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 has it taken so long? Is this kind of a failure of science?
Science Vs
Fluoride: Is Your Water Safe?
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. Yes, what's different. And so someone does this analysis and McKay finally gets an answer after three decades of searching. It was the fluoride.
Science Vs
Fluoride: Is Your Water Safe?
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 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.
Science Vs
Fluoride: Is Your Water Safe?
We didn't get sealants or brush our teeth with fluoridated toothpaste. Right. So it's something like putting fluoride in the water had this big potential to make a huge difference because 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, tools in the toolbox to help our teeth.
Science Vs
Fluoride: Is Your Water Safe?
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? Right. And so that's what I wanted to talk about with Lindsay McLaren. She's a professor in community health sciences at the University of Calgary in Canada.
Science Vs
Fluoride: Is Your Water Safe?
And this all first got on her radar back in 2011 when her city decided to stop putting fluoride in the water.
Science Vs
Fluoride: Is Your Water Safe?
And Lindsay and some of her public health 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. Yeah.
Science Vs
Fluoride: Is Your Water Safe?
So Lindsay was like, yeah, let's do some science here. Like we're taking fluoride out of the water. Will our teeth get crappier?
Science Vs
Fluoride: Is Your Water Safe?
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 seven years old.
Science Vs
Fluoride: Is Your Water Safe?
And they started by sending out teams of dental hygienists and researchers to schools in Calgary to check their teeth.
Science Vs
Fluoride: Is Your Water Safe?
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.
Science Vs
Fluoride: Is Your Water Safe?
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. So what did they find? You're stringing me along like floss here. Okay, okay. So, yeah, we've got 5,000 second graders across these two cities.
Science Vs
Fluoride: Is Your Water Safe?
And now they can finally see, did the kids who grow up with fluoride added to the water have fewer cavities compared to the kids in Calgary?
Science Vs
Fluoride: Is Your Water Safe?
So other studies generally find the same thing. Kids do tend to get more cavities when they grow up without fluoridated water.
Science Vs
Fluoride: Is Your Water Safe?
Yeah, these kids are getting fewer cavities, and I know maybe you're thinking... Who cares? Little cavity here or there. Maybe it doesn't matter so much. Right. It's just their baby teeth. They're going to get more. 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.
Science Vs
Fluoride: Is Your Water Safe?
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.
Science Vs
Fluoride: Is Your Water Safe?
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.
Science Vs
Fluoride: Is Your Water Safe?
And we also have evidence that fluoride is particularly good for kids who come from poorer families. Like in Lindsay'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.
Science Vs
Fluoride: Is Your Water Safe?
Well, 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.
Science Vs
Fluoride: Is Your Water Safe?
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. Wow.
Science Vs
Fluoride: Is Your Water Safe?
So, yeah, it's like pretty convincing to me that fluoride in the water is still helping our teeth. Right. Which brings us back to Lindsay'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!
Science Vs
Fluoride: Is Your Water Safe?
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.
Science Vs
Fluoride: Is Your Water Safe?
Yeah, it seems like it. Like they had a vote and 62% of the people said, yes, we want to fluoridate our water again.
Science Vs
Fluoride: Is Your Water Safe?
Yeah, so her study got a lot of attention, like even in the U.S. Here's some of that coverage.
Science Vs
Fluoride: Is Your Water Safe?
So yeah, I asked Lindsay like where she lands after all this. Should we be putting fluoride in the water?
Science Vs
Fluoride: Is Your Water Safe?
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.
Science Vs
Fluoride: Is Your Water Safe?
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.
Science Vs
Fluoride: Is Your Water Safe?
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. Yeah. And he'd been thinking more and more about this research.
Science Vs
Fluoride: Is Your Water Safe?
Okay, there's so much controversy right now around water fluoridation. I know. Which we'll get to. Okay. 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 so. How did it all start? Well, it's actually a detective story. It starts in 1901.
Science Vs
Fluoride: Is Your Water Safe?
And I asked him, like, all right, like, if you're in charge of the machine, do you cut it off?
Science Vs
Fluoride: Is Your Water Safe?
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, like, keep turning this over in my brain. I was going to say, I was just...
Science Vs
Fluoride: Is Your Water Safe?
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 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.
Science Vs
Fluoride: Is Your Water Safe?
Where, like, 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.
Science Vs
Fluoride: Is Your Water Safe?
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.
Science Vs
Fluoride: Is Your Water Safe?
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. So this was the beginning. Yeah, this is like the birth story of water fluoridation.
Science Vs
Fluoride: Is Your Water Safe?
So in 1945, Grand Rapids, Michigan was the first city in the U.S. to add fluoride to the water. And people were really excited. The government released a PSA about it.
Science Vs
Fluoride: Is Your Water Safe?
It's working. Yeah, they found that it slashed rates of tooth decay by as much as 70%. Wow.
Science Vs
Fluoride: Is Your Water Safe?
And after that, we started fluoridating water in most of the US, 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.
Science Vs
Fluoride: Is Your Water Safe?
Well, there's actually been some opposition to this from the start, but recently things are really heating up, even at the highest levels. So Robert F. Kennedy Jr., who leads the Department of Health and Human Services, he thinks that fluoride is dangerous.
Science Vs
Fluoride: Is Your Water Safe?
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.
Science Vs
Fluoride: Is Your Water Safe?
And on top of all the dangers of fluoride, people are also saying now that it doesn't even work to prevent cavities anymore. Now that we have better dental care.
Science Vs
Fluoride: Is Your Water Safe?
Is fluoride really the hero that we 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 U.S.
Science Vs
Fluoride: Is Your Water Safe?
Yeah, that's the question. And just to say that, like, the research on this was, like, not at all what I was expecting it to be.
Science Vs
Fluoride: Is Your Water Safe?
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.
Science Vs
Fluoride: Is Your Water Safe?
The case study said that, quote, after 24 hours of intractable vomiting, a 41-year-old man was found dead at home.
Science Vs
Fluoride: Is Your Water Safe?
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.
Science Vs
Fluoride: Is Your Water Safe?
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.
Science Vs
Fluoride: Is Your Water Safe?
And at really high levels, it can stop your heart. Okay, right.
Science Vs
Fluoride: Is Your Water Safe?
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.
Science Vs
Fluoride: Is Your Water Safe?
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. Right. But like 10 years ago, we checked to see how many kids in the U.S. have this, and it was 70%.
Science Vs
Fluoride: Is Your Water Safe?
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.
Science Vs
Fluoride: Is Your Water Safe?
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.
Science Vs
Fluoride: Is Your Water Safe?
Yeah. So Ashley first remembers when she heard about this idea that fluoride might be bad for us. She was with a family member.
Science Vs
Fluoride: Is Your Water Safe?
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.
Science Vs
Fluoride: Is Your Water Safe?
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.
Science Vs
Fluoride: Is Your Water Safe?
Yeah. And some of those studies had been finding that people who lived in these areas had lower IQs.
Science Vs
Fluoride: Is Your Water Safe?
I was like, huh. 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.
Science Vs
Fluoride: Is Your Water Safe?
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. And that kind of roughly maps out to how much fluoride you're taking in.
Science Vs
Fluoride: Is Your Water Safe?
But by the way, this isn't just looking at like fluoride from the water, because 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...
Science Vs
Fluoride: Is Your Water Safe?
So, yeah, the researchers here are looking at kind of like overall fluoride exposure. Okay. And then 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.
Science Vs
Fluoride: Is Your Water Safe?
Like people will say like, oh, my kid has temper tantrums like all the time or like, oh, that's really rare. It's like that kind of a thing.
Science Vs
Fluoride: Is Your Water Safe?
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 3.
Science Vs
Fluoride: Is Your Water Safe?
So Ashley was working from home looking at her data on her laptop when she saw the results.
Science Vs
Fluoride: Is Your Water Safe?
They did have more temper tantrums. They had more anxiety and symptoms linked to autism.
Science Vs
Fluoride: Is Your Water Safe?
Well, it wasn't like every kid who had some fluoride in the water got anxiety. Right. 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.
Science Vs
Fluoride: Is Your Water Safe?
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. Hmm. So, like, they had no idea at first, like, what was going on here.
Science Vs
Fluoride: Is Your Water Safe?
Yeah, 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 saw this. There was like a turning point for me where I was like, what? Like fluoride might actually be doing something bad here? Yeah.
Science Vs
Fluoride: Is Your Water Safe?
Okay, so I found eight studies altogether that basically did what Ashley did. So they looked at prenatal fluoride exposure.
Today, Explained
Methamphetamine: The most misunderstood drug?
I tried that for one report that I did. This was not for Science Fest. It was for something else. And I just was so embarrassed and thought I sounded like such a fool. I never did it again.
Today, Explained
Methamphetamine: The most misunderstood drug?
I do have to play this bonkers ad that my editor remembers hearing a lot when she grew up in the Midwest.
Today, Explained
Methamphetamine: The most misunderstood drug?
So when it comes to science versus math.
Today, Explained
Methamphetamine: The most misunderstood drug?
And now that I know the evidence, it's definitely a naughty drug.
Today, Explained
Methamphetamine: The most misunderstood drug?
But you might catch me humming a little ditty about it.
Today, Explained
Methamphetamine: The most misunderstood drug?
How much were you thinking about your own experience as you were writing these studies? All the time.
Today, Explained
Methamphetamine: The most misunderstood drug?
She was actually never that worried that taking a bit of meth a handful of times would stop her from finishing her thesis, largely because of that research that shows the brain can recover.