I have a rough history with cavities, mainly due to the simultaneous bouts of my ADHD and depression. Ask nearly any dentist—fluoride helps prevent cavities and tooth decay, so I use fluoridated toothpaste. I’m also a fan of water fluoridation and believe that it was one of the most impressive public health initiatives of the 1900s.
Water fluoridation began in the U.S. in the 1940s as a public health strategy to reduce tooth decay—and it worked. Cities that fluoridated their water saw dramatic reductions in dental caries, particularly in kids. Over time, fluoridation became standard in many municipalities across the U.S.
Since implementing this policy, important questions have arisen: Does central water fluoridation make as much sense today as it did in the past? Could it be doing more harm than good?
Policy pushback
For decades, there have been concerns about unintended health consequences from added fluoride, especially for the brain. In 2024, a study found that fluoride exposure in pregnancy was related to an increased risk for neurobehavioral problems in the US. Another study from January (2025) indicating that overfluoridation of the water was associated with reduced IQ.
And yeah, those are big deals. I don’t want to underscore those findings at all. In reviewing the two studies, I found them to be well-performed science; that is, I do my best to find flaws in research, and these data appear to be sound. If you’re curious about all the research on fluoride and cognitive development, check out this article.
And then, a paper published just last month (April 2025) just adds fuel to the political fire—claiming that fluoridated water is associated with an increased risk of ADHD and autism diagnoses in children.
Let’s break it down – what they found, what it means, and what they got wrong.
What the paper says
The authors looked at Florida Medicaid data from 1990-2012, that followed 73,254 kids across counties in Florida that do or don’t fluoridate their water. They checked how many people had claims for:
- ADHD
- Autism Spectrum Disorder (ASD)
- Tooth decay
They found:
- No increased likelihood of ADHD in kids from fluoridated counties
- A 5.6% increased likelihood of autism in those counties
- And a 0.35% reduced likelihood of tooth decay (billed as dental carries) in those counties as well
At first glance, this seems like a serious trade-off: better teeth, but higher neurodevelopmental risk? Okay, slow your roll: That is what sensationalist newspapers and wellness grifters who want to sell you their unfluoridated toothpaste do—we’re smarter than that! Let’s dig in.
What they got wrong and why
Red flag #1: The authors are hacks
David and Mark Geier are a father-son duo who have been widely discredited as honest, unbiased researchers in the scientific community. They practice medicine without licensure, have had many studies pulled and discredited, published studies in fake Journals “peer-reviewed” by a known wellness grifter, and are regularly profiting off the debunked claim that vaccines cause autism.
David Geier, was appointed by RFK Jr., to lead a study to prove once and for all the link between autism and vaccines (which, spoiler-alert, considering his bias we know what is going to be found, and considering their data manipulation tactics, we know how they’re going to find it).
I’m not typically one to be skeptical of the authors themselves since researchers go through significant training to reduce their bias and ensure proper data analysis, but I don’t have much hope here considering the track record.
Science is great. Manipulating science for profit and personal gain isn’t.
Red flag #2: Confounding variables
In science, we must control for all variables or clearly call out what variables we cannot cover or include in our research: This is Academic Writing 101. Our sensationalist authors accounted for date of birth, gender, race, maternal health status, environmental toxicant exposure, and undisclosed “socioeconomic factors”. Sounds great, right? But they didn’t control for the most important variable: genetic susceptibility, which we know from extensive research is a huge factor.
Red flag #3: ICD-9 billing codes to “diagnose” kids
Here’s the best part, and the biggest flaw in the study: Even if these are great scientists who have sterling reputations and accounted for every variable, their data is bogus. They used ICD-9 billing codes to determine whether a child had ASD, ADHD, or another condition.
Billing codes are not clinical diagnoses. Here’s why:
- Providers may code a condition provisionally to justify a referral or medication trial.
- ICD-9 codes don’t distinguish severity, duration, or confirmed diagnosis.
- Many children—especially those in rural or under-resourced communities—are underdiagnosed or misdiagnosed.
- These codes were collected from Medicaid claims, which may reflect insurance dynamics more than actual health status.
It’s like looking at who bought cold medicine and assuming they all had pneumonia.
The authors tried to validate these codes using “positive predictive value,” but even a PPV of 0.8 or 0.9 still means 10–20% of cases are likely wrong.
Instead, they should have used actual validated questionnaires and DSM diagnoses. This was an issue with a previous study they did on autism and vaccines that I covered over on Instagram.
Red flag #4: Location
Last but certainly not least, they assumed that county fluoridation status = individual fluoride exposure, but people:
- Drink bottled water,
- Move between counties,
- Have different absorption or avoidance behaviors.
Even more importantly, counties that fluoridate their water may also differ in other ways:
- Rural vs. urban settings
- Availability of mental health providers,
- Education levels, Socioeconomic status, pollution, etc.
For example: if fluoridated counties also have better access to ADHD specialists, of course, you’ll see more diagnoses – not because fluoride causes ADHD, but because more kids are able to get evaluated.
Instead, they should have regularly measured urinary fluoride levels throughout the years, which would indicate exposure, and then used the county as a confounding variable to control for.
Final thoughts
There are, unfortunately, many red flags with this study that we need to be aware of. The concept of this study is so important, and it is unfortunate that it was so poorly conducted. We see that they used data manipulation tactics that are consistent with previous papers that got them discredited in the first place.
The results of this paper suggest that fluoride might be hurting kids’ brains more than helping their teeth. When we look at the statistics, we find that fluoridation across the years is associated with a:
- 5.6% increased risk of autism spectrum disorder
- 3.8% increased risk of intellectual disability
- 1.5% increased risk of specific delays in development
- No increased risk for ADHD.
Fluoridated water exposure in the first year of life was associated with a 1% increased risk for all four of those. And yeah, that can sound a little scary.
However, we want to remember all of those red flags above. Considering all of those, it is nearly impossible to say if this increased risk is even true. We truly just need better evidence and a better design.
And if it was true? Well, that increased risk is very, very small. At the end of the day, because they didn’t control for the most important confounding factor (genetics) while at the same time using billing codes instead of real evidence of developmental delays, we really don’t get anything meaningful out of this study regarding neurocognitive development and fluoride.
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