Fluoride causes low IQ?
Don't throw the fluoride out with the bath water just yet...
Study links high fluoride exposure to lower IQ in children. This was the headline of a New York Times article in January of 2025. I get it, that’s scary to hear. Before we get upset and throw the fluoride out with the bath water, let’s better understand where this headline came from.
The article was based on this paper published in JAMA Pediatrics in January 2025. The paper was a systematic review and meta-analysis (MA) of of 74 cross-sectional and prospective cohort studies. Basically, they grab all the data from studies that meet their inclusion criteria (i.e. they are appropriately similar), take the data from all of them, run some numbers, and come up with some overall conclusions based on amplified data that might be missed by each of the smaller individual studies. The TLDR; this MA found that for each incremental increase in fluoride intake, children’s IQ scores went down! This might seem bad, but guess what; there is important nuance to unpack. Let’s go through it.
Why fluoride anyway?
Fluoride deficiency can lead to several significant health problems, particularly affecting dental and bone health. According to the World Health Organization (WHO), the primary consequences include:
Dental Issues: Without adequate fluoride, individuals are at higher risk of dental caries (cavities). An article in the Journal of Public Health Dentistry demonstrates that individuals who used fluoridated toothpaste and assessed the effects on dental caries. They found that time those individuals who lived in areas with fluoridated water supplies had less decay regardless of fluorodated toothpaste use.
Weakened Tooth Enamel: Fluoride is crucial for the remineralization of tooth enamel. An Clinical Oral Investigations study showed that fluoride application increased mineralization of caries type lesions in enamel in bovine models.
Enamel fluorosis: Too much fluoride, particularly in the early years, can lead to enamel fluorosis, which results in streaks and staining of primary teeth, which can have a cosmetic effect. This is important, as we will see later, because the presence of dental fluorosis is an accepted surrogate for how much fluoride is actually consumed.
Bone fluorosis: Interruption to calcium metabolism from high exposures, can cause reduced bone density and increase fracture risk. Studies from China and India have demonstrated this to happen at doses of 14mg/day.
So how much fluoride is in the water?
According to the CDC, the optimal fluoride level in drinking water is 0.7 milligrams per liter (mg/L). This recommendation was updated in 2015 to replace the previous range of 0.7–1.2 mg/L.
The WHO recommends a guideline value of 1.5 mg/L as the maximum allowable fluoride concentration in drinking water. However, they note that this value should be considered in the context of local conditions, as factors like climate and water consumption patterns can affect optimal levels. For example, some areas around the world have naturally very high concentrations of fluoride in the water supply, and filters may be required to get the concentrations down to the recommended levels.
How much am I drinking?
Now that we understand why fluoride is important and what the levels in our water supply are, we can understand how much you are getting exposed to in a day. For example, if you drink 4L/day of water with a concentration of 1mg/L, you will ingest 4mg of fluoride per day. Remember studies assessing the risk of bone fluorodosis they found that this occurs at a dose of 14mg per day on average. How much water do you drink per day?
What about fluoride and IQ?
Let’s get back to the paper that started all of this. So they did a systematic review (constructed inclusion criteria to find similar smaller studies), did a meta-analysis (grabbed the small datasets from each study and “turned up the volume” on the signal from those studies). The studies were all conducted in countries with naturally higher concentrations of fluoride in the water. The levels that were used as cut points for assessment were 1.5mg/L, 2mg/L and 4mg/L. They assessed the childrens’ IQ using a range of different tests. They found that higher the concentrations of fluoride consumed, the lower the IQ. They also tried to confirm that the kids also were actually consuming. To do this you need a biomarker and this study looked at urinary fluoride output. It seems intuitive to think that the more you consume, the more you pee out. It’s not that simple, the metabolism of the mineral can be altered by many things, gut absorption when consuming with other foods or bone absorption of the mineral. An editorial that was published with this paper suggested that urinary output of fluoride may not be the best biomarker to assess actual intake. Another paper from Australia used dental fluorosis as the “biomarker” of actual intake.
Any time you do a MA, authors should perform a “risk of bias” analysis. This analysis evaluates the quality and reliability of the included studies. The researchers examine factors like study design, methodology, participant selection, data collection, and potential conflicts of interest. This helps determine how much confidence we can place in the results. Studies with high risk of bias might skew the overall findings, while those with low risk of bias are generally more trustworthy, or can make you more confident in your findings.
In this paper, the authors noted several potential sources of bias in the included studies:
Many studies were from regions with naturally high fluoride levels, which might not represent typical exposure scenarios (particularly in many parts of the US)
Different IQ testing methods were used across studies, making direct comparisons challenging
Some studies didn't adequately control for confounding factors like socioeconomic status or parental education
The timing and duration of fluoride exposure varied significantly between studies
The study did perform two separate analyses, one with all studies, and just the studies with low risk of bias (12 in total). The inverse relationship was held with the low risk of bias studies (although the differences were small).
So how much is my score going to go down?
Great question. Here’s the table from the paper:
So at most, IQ was decreased by around 7 points (1 study from Mexico) down to less than 1 point with the highest risk at very high levels of water fluoride concentrations. I ask readers, what is the difference between a person with an IQ of 102 and an IQ of 109? Food for thought.
When stratifying change in IQ by urine fluoride concentrations, they found that for every 1mg/L urine fluoride increase, there was about a 1 point drop in IQ score. On average, to increase your urine fluoride output by 1mg/L, you would need to consume roughly 3mg/L of fluoride in your water.
How does this paper fit with other studies?
Here are two other studies that try to answer a similar question;
Veneri et al was also a MA which showed no association in studies with low risk of bias
A study out of Australia (a much better correlate for the US) also showed no negative effect on IQ (in fact, a slightly better IQ with fluoride exposure) and no risk of dental fluorosis with the addition of fluoride to the drinking supply.
I live in America, how does this affect me?
First, I would question why this study has any relevance to an American population. Even if we say that there is a strong linear relationship between increasing concentration of fluoride and decreasing IQ and assume that the studies were all low risk of bias. Here in America, we simply don’t get exposed to that much fluoride (currently 0.7mg/L in places which supplement the water supply). If we know that consuming fluoride in drinking water reduces the risk of dental caries and doesn’t increase the risk of negative outcomes like bone/dental fluorosis or reduced IQ, why are we even having this conversation?
You know who does fearmonger about fluoride in the water?
Our current secretary of Health and Human Services; Robert F. Kennedy Jr. Here are some articles on his website claiming that fluoride in drinking water is "linked to lower IQ in children." This is a perfect example of cherry-picking data and misrepresenting scientific findings to promote fear. I’ve said it once, and I’ll say it again: he is literally the WORST person imaginable to hold this position.
As you can imagine, many scientists around the US and the world are concerned with how much of a hard turn the US is making against scientific institutions. I hope that articles like this help you to better understand clickbait headlines from actual interpretation of science and NOT GET GRIFTED!
As always, this is my interpretation of this data. You may find holes in what I am saying here and that’s great. Reach out and let me know where I went wrong.
Peace and Love.
Dr Cois
