What Does the Evidence Say About Fluoride Lowering IQ?

Fluoride is in the news again, and for good reason. In a new review of the data published this month, scientists found evidence that higher levels of fluoride exposure are associated with lower IQs in infants and very young children.

Historically, fluoride was added to our water to strengthen tooth enamel, which helps prevent tooth decay. Improved childhood dental health is known to in turn reduce school absences, lead to less expensive 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 — may be riskier than previously thought. They found that children exposed to higher levels of fluoride in their earliest years of life had significantly lower IQ scores, particularly between one and two points, than children exposed to lower levels of fluoride.

the review, published c JAMA Pediatricsisn’t the only recent study to cast some shade on fluoride. A study from last May, for example, found link between higher fluoride exposure in pregnant women and a greater risk of their children being diagnosed with neurobehavioral problems by age three. Some scientists have too interviewed recently whether water fluoridation is now necessary to get the benefits of fluoride, since people in many parts of the world can get fluoride from their toothpaste products.

However, the scientific debate about the positive and negative effects of fluoride is not one-sided. Some scientists they have criticized the methodology and interpretations of the recent review, for example. And the study itself could not find convincing evidence association of lower IQ with low fluoride exposure, including levels recommended for US drinking water (0.7 milligrams per liter). They have other reviews similarly failed to find an association between relatively low fluoride exposure and loss of IQ 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 to support a potential link. Robert F. Kennedy Jr., who is set to head the US Department of Health and Human Services under the Trump administration, has argued that fluoride is linked to bone cancer, for example, although most studies do not significant association with cancer.

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

Jay Kumar

Retired epidemiologist, dental health specialist and co-author of a meta-analysis in 2023 on the potential effects of fluoride on IQ in children.

Findings that high levels of fluoride in drinking water in rural areas of China, India, Pakistan and Iran are associated with IQ deficits are not new. The authors could not attribute the IQ deficits to fluoride in the water because the quality of the study was low. These studies measured fluoride in drinking water and IQ in children simultaneously. For example, it may be that parents with higher IQs moved from regions to avoid high fluoride water because of the well-known risk to teeth and bones, and hence the absence of families with higher IQs. intelligence can lead to the relationship, not the other way around. This potential bias is sometimes known as the “cart-before-the-horse bias.” Additionally, animal and human studies cannot explain how fluoride might affect the brain.

We published a study titled “Association between low fluoride exposure and children’s intelligence: a meta-analysis related to community water fluoridation.” In this article, we answered the research question: Does fluoride exposure recommended for caries prevention reduce children’s cognitive abilities and IQ? Fluoride is recommended at 0.7 mg/L for US public water supplies.

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

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

Bruce Lanfear

An epidemiologist at Simon Fraser University who has studied how fluoride exposure in pregnant women can affect the later development of their children.

Fluoride is a reactive chemical that binds strongly to calcium and metals. In 1944 the Journal of the American Dental Association described fluoridation as “impressively attractive” for preventing tooth decay, but warned of the risks of adding a “highly toxic substance” to drinking water. Today, over 70% of Americans drink tap water fluoridated at about 0.7 (parts per million, or ppm), considered “optimal.” Fluoride is also present in toothpaste (1000–1500 ppm), black teas (1–6 ppm), foods such as sardines and anchovies (2–4 mg/100 g), some medications (eg, Prozac, Lipitor), and pesticides. treated products such as raisins. Over the past 50 years, fluoride intake has increased, contributing to an increase in dental fluorosis – discoloration or staining of teeth due to excessive exposure to fluoride during development.

What did the study find?

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

Are these findings relevant to fluoridated communities?

Critics claim that no IQ deficits have been found at water fluoride levels below 1.5 mg/L, but this is misleading. First, no visible threshold has been identified. Second, fluoride in water is only one source of exposure, and total fluoride intake must be considered for risk assessment. Urinary fluoride, a snapshot of total fluoride intake, shows a significant reduction in IQ in children at concentrations typically found in fluoridated communities.

For example, a Canadian study found that 25% of pregnant women in optimally fluoridated areas had urinary fluoride levels above 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 such as fluoride and arsenic.

Does fluoridation prevent tooth decay?

It is time to critically review the benefits of fluoride. 2024 Update on A Cochrane review found little or no benefit from water fluoridation in studies conducted after 1975, when fluoride toothpaste became widely available. Fluoride’s caries-preventing effects are primarily local, not systemic, and do not provide benefit until teeth erupt.

Should you be worried?

Public health agencies should reevaluate fluoridation guidelines based on new evidence. Until then, consider the following precautions:

• Pregnant women and young children: Avoid fluoridated water and other sources of fluoride, such as black tea.
• Infant milk: Use non-fluoridated water to mix formula; breast milk contains a minimal amount of fluoride.
• Children’s toothpaste: Use only a rice-sized amount of fluoride toothpaste and make sure that children do not swallow the toothpaste.

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

Sarah Evans

Assistant Professor of Environmental Medicine and Climate Sciences at the Icahn School of Medicine at Mount Sinai, who studies how early life exposures can affect behavior and cognition.

It is important to note that none of the studies included in the meta-analysis (NTP) were conducted in the United States, where the recommended concentration of fluoride in drinking water is 0.7 mg/L—more than 50% lower lower than the fluoride exposure measured in most of the communities studied. Although more studies are needed to examine the impact of lower fluoride exposure, in 2023 meta-analysis found no association between fluoride and child IQ in communities with drinking water levels similar to those in the US.

While there are no studies to date to suggest a risk of harm at the 0.7 mg/L fluoride most commonly found in US drinking water, an estimated 2.9 million Americans and 180 million people worldwide may be exposed of fluoride at levels above WHO guidelines due to the presence of high levels of natural fluoride in some areas. Individuals living in these areas may be at greater risk of exposure at levels that were associated with lower 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, can lead to exposures above the daily recommendation. Comprehensive studies that measure individual exposure levels of the US population from all sources of fluoride are needed.

Although about three-quarters of the US water supply is fluoridated, this practice is not permitted 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 to only 16% of New Jersey residents. People interested in knowing the level of fluoride in their drinking water should contact their water supplier. If you live in an area with high levels of fluoride from natural sources and are pregnant or have small children, it is possible to reduce fluoride exposure by using reverse osmosis filtration. Bottled water is not regulated for fluoride or other contaminants and is generally not recommended. If you consume water from a public water supply or a private well that does not contain fluoride, it is important to practice good dental hygiene by using fluoride toothpaste and mouthwash and regular dental visits.

The results of this study will likely lead to an increase in the number of communities asking whether to end water fluoridation. Although there is some evidence that the growth of fluoride products and improved access to dental care has reduced the need for fluoridated water, several studies have shown a dramatic increase in childhood cavities and the need for dental treatment in communities that have removed fluoride from the 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 effects of high levels of fluoride exposure on brain development, it also highlights the need for well-designed longitudinal studies that measure fluoride exposure at the individual level over time to confirm whether associations with IQ or other neurological outcomes development continues at the low levels seen by most Americans. In addition, it highlights the need to investigate practices that reduce the risk of fluoride exposure above recommended levels in areas where natural fluoride levels are high, and review practices that increase access to routine dental care.