What Does the Evidence Say About Fluoride Lowering IQ?

Fluoride is once again in the news, and not for a great reason. In a new review of the data published this month, scientists have found evidence that higher levels of fluoride exposure are associated with declined IQ in infants and very young children.

Historically, fluoride has been added to our water to strengthen our tooth enamel, which helps prevent cavities. Improved childhood dental health in turn is known to reduce sick days from school, lead to fewer costly dental procedures, and possibly even reduce the risk of cardiovascular disease later in life.

But this new research, conducted by scientists at the NIH’s National Toxicology Program, suggests that fluoride exposure—and by extension water fluoridation—might be riskier than assumed. They found that children exposed to higher fluoride levels during their earliest years of life had noticeably lower IQ scores, specifically between one and two points, than children exposed to lower levels of fluoride.

The review, published in JAMA Pediatrics, isn’t the only recent study to throw some shade at fluoride. A study from last May, for instance, found a link between higher fluoride exposure in pregnant women and a greater risk of their children later being diagnosed with neurobehavioral problems by age three. Some scientists have also questioned recently whether water fluoridation is needed to obtain the benefits of fluoride anymore, since people in many parts of the world can get fluoride from their toothpaste products.

The scientific debate over fluoride’s positives and negatives isn’t one-sided, however. Some scientists have criticized the methodology and interpretations of the recent review, for instance. And the study itself couldn’t find conclusive evidence linking lowered IQ to low fluoride exposure, including levels recommended for U.S. drinking water (0.7 milligrams per liter). Other reviews have similarly failed to find a link between relatively low fluoride exposure and IQ loss or impaired development (including after the introduction of a fluoridation program).

Some critics of fluoridation have also tried to blame fluoride for other health problems that have much less evidence supporting a potential connection. Robert F. Kennedy Jr., who’s in line to head the U.S. Department of Health and Human Services under the Trump administration, has argued that fluoride is associated with bone cancer, for instance, despite the majority of studies finding no significant cancer link.

For this Giz Asks, we reached out to experts to share their thoughts on the latest study, the science surrounding fluoride, and the potential implications of this research. The following responses have been lightly edited and condensed for clarity.

Jay Kumar

A retired epidemiologist specializing in dental health and co-author of a meta-analysis in 2023 on fluoride’s potential IQ effects in children.

The findings that high fluoride levels in drinking water in rural areas of China, India, Pakistan, and Iran are associated with IQ deficits are not new. The authors cannot attribute the IQ deficits to fluoride in water because the study quality is low. These studies measured fluoride in drinking water and IQ in children at the same time. For example, it could be that parents with higher IQs had moved from regions to avoid high-fluoride water because of its well-known risk to teeth and bones, and therefore, the absence of higher IQ families may drive the association rather than the reverse. This potential bias is sometimes known as the “cart-before-the-horse bias.” Also, studies conducted in animals and humans cannot explain how fluoride could affect the brain.

We published a study titled “Association between low fluoride exposure and children’s intelligence: a meta-analysis relevant to community water fluoridation.” In this paper, we answered the research question: Does fluoride exposure recommended for the prevention of tooth decay decrease children’s cognition and IQ scores? Fluoride is recommended at 0.7 mg/L for U.S. community water supplies.

Our study concluded that fluoride exposure at approximately twice the concentration used in community water fluoridation (less than 1.5 mg/L) is not associated with lower IQ scores in children. However, we underscore the necessity for more research to determine whether fluoride naturally occurring in drinking water exceeding 1.5 mg/L causes IQ deficits.

A recent Australian study by Do et al. reaffirmed the findings from Canada, New Zealand, and Spain that the IQ scores are similar in fluoridated and non-fluoridated areas.

Bruce Lanphear

An epidemiologist at Simon Fraser University who has studied how fluoride exposure in pregnant women may affect their children’s later development.

Fluoride is a reactive chemical that binds strongly to calcium and metals. In 1944, the Journal of the American Dental Association described fluoridation as “spectacularly attractive” for preventing cavities but warned of the risks of adding a “highly toxic substance” to drinking water. Today, over 70% of Americans drink tap water fluoridated at around 0.7 [parts per million, or ppm], considered “optimal.” Fluoride is also present in toothpaste (1,000–1,500 ppm), black teas (1–6 ppm), foods like sardines and anchovies (2–4 mg/100 g), certain medications (e.g., Prozac, Lipitor), and pesticide-treated produce like raisins. Over the past 50 years, fluoride ingestion has increased, contributing to a rise in dental fluorosis—discoloration or mottling of teeth due to excessive fluoride exposure during development.

What Did the Study Find?

Taylor’s team reviewed 74 studies from 10 countries linking fluoride exposure to IQ scores. While many early studies were of lower quality, a meta-analysis of high-quality research revealed that a 1 ppm increase in urinary fluoride was associated with a 1.2 point IQ reduction in children, even at levels below 1.5 ppm. Although these IQ decrements are small, they have substantial population-level implications, particularly for children who are exposed to other toxic chemicals, such as lead or air pollution.

Are These Findings Relevant to Fluoridated Communities?

Critics argue that no IQ deficits were found at water fluoride levels less than 1.5 mg/L, but this is misleading. First, no apparent threshold was identified. Second, water fluoride is just one source of exposure, and total fluoride intake must be considered for risk assessment. Urinary fluoride, a snapshot of overall fluoride intake, showed significant IQ reductions in children at concentrations commonly found in fluoridated communities.

For example, a Canadian study found that 25% of pregnant women in optimally fluoridated areas had urinary fluoride levels higher than 1 ppm, and 5% exceeded 1.5 ppm. While some question the reliability of urinary fluoride measurements, they are widely used by epidemiologists to assess exposure to short-lived chemicals like fluoride and arsenic.

Does Fluoridation Protect Against Tooth Decay?

It is time to critically review the benefits of fluoride. A 2024 update of the Cochrane review found little to no benefit from water fluoridation in studies conducted after 1975, when fluoride toothpaste became widespread. Fluoride’s cavity-preventing effects are primarily topical, not systemic, and provide no benefit until teeth erupt.

Should You Be Concerned?

Public health agencies must re-evaluate fluoridation guidelines based on new evidence. Until then, consider these precautions:

• Pregnant women and young children: Avoid fluoridated water and other sources of fluoride, like black tea.
• Infant formula: Use non-fluoridated water for mixing formula; breastmilk contains minimal fluoride.
• Children’s toothpaste: Use only a rice-sized amount of fluoride toothpaste and make sure children don’t swallow toothpaste.

By taking these steps, you can minimize fluoride exposure during critical developmental periods.

Sarah Evans

An assistant professor of Environmental Medicine and Climate Science at the Icahn School of Medicine at Mount Sinai who studies how people’s early life exposures can impact behavior and cognition.

It’s important to note that none of the studies included in the [NTP] meta-analysis were conducted in the United States, where the recommended fluoride concentration in drinking water is 0.7 mg/L—more than 50% lower than the fluoride exposure measured in most of the communities studied. While more studies are needed to examine the impacts of lower level fluoride exposure, a 2023 meta-analysis found no link between fluoride and child IQ in communities with drinking water levels similar to the US.

While to date there are no studies that suggest risk of harm at the 0.7mg/L fluoride most commonly found in US drinking water, an estimated 2.9 million Americans and 180 million people worldwide may be exposed to fluoride at levels above the WHO guideline due to the presence of high levels of natural fluoride in some areas. Individuals residing in these areas may be at greater risk of exposure to levels that were associated with decreased child IQ in the study. In addition, the inclusion of fluoride in dental products and treatments as well as its natural presence in some foods and beverages may lead to exposures above the daily recommendation. Comprehensive studies that measure individual levels of exposure in the US population from all sources of fluoride are needed.

While around three-fourths of the US water supply is fluoridated, this practice is not mandated by the federal government and is under state or local control, so fluoridation practices vary widely across the country. For example, 99.9% of Kentucky residents receive fluoride in their drinking water compared with only 16% of New Jersey residents. Individuals who are interested to know the level of fluoride in their drinking water should contact their water supplier. If you live in an area with high fluoride from natural sources and are pregnant or have young children, it is possible to reduce fluoride exposure through reverse osmosis filtration. Bottled water is not regulated for the presence of fluoride or other contaminants and is generally not recommended. If you consume water from a public supply or private well that does not have fluoride, it’s important to practice good dental hygiene through the use of fluoride-containing toothpaste and mouthwash and regular dental visits.

The findings of this study are likely to lead to an increase in the number of communities who are questioning whether to discontinue water fluoridation. Although there is some evidence that the rise of products containing fluoride and improved access to dental care have reduced the need for fluoridated water, several studies show a dramatic increase in child tooth decay and need for dental treatments in communities that have removed fluoride from drinking water, suggesting that water fluoridation remains an effective and necessary public health intervention.

While the recent meta-analysis by Taylor et al. suggests adverse impacts of high levels of fluoride exposure on brain development, it also highlights a need for well-designed longitudinal studies that measure individual-level fluoride exposure over time to confirm whether associations with IQ or other neurodevelopmental outcomes persist at the low levels experienced by most Americans. In addition, it highlights the need for research into practices that reduce the risk of exposure to fluoride above the recommended levels in areas where natural fluoride levels are high and a reexamination of practices that increase access to routine dental care.