Controversy about fluoride in drinking water may have you wondering whether the mineral poses health risks. Learn what the science says.
Communities in the United States have been adding fluoride to the water supply since the 1940s, and that effort has led to better dental health for millions of Americans. But even from the beginning, there has been skepticism around that effort.
Before his February 2025 confirmation, U.S. Health and Human Services Secretary Robert F. Kennedy Jr. called fluoride “an industrial waste associated with arthritis, bone fractures, bone cancer, IQ loss, neurodevelopmental disorders, and thyroid disease,” in a post on X. Once in office, he vowed to get fluoride out of drinking water across the United States.
Since then, states including Utah and Florida have passed laws to ban fluoride from public water supplies.
Read on to find out why fluoride is added to drinking water, and what research has determined about its health risks.
Roughly 3 in 4 Americans today live in communities with fluoridated water, according to the Centers for Disease Control and Prevention (CDC). The agency considers the addition of fluoride to water to be one of the most important public health interventions of the past century because it reduces cavities by about 25 percent.
“The benefits of fluoride have been established around the world for decades,” says Marcelo W.B. Araujo, DDS, PhD, a professor and the dean of the school of dental medicine at the University at Buffalo in New York.
While almost all water contains fluoride, a naturally occurring mineral, there typically isn’t enough to ward off cavities. The recommended fluoride level for cavity prevention is 0.7 milligrams per liter (mg/L) of water — roughly three drops per 55 gallon container.
Fluoride in drinking water prevents tooth decay in adults and children, even when they have access to fluoride from other sources like toothpaste, according to the American Dental Association (ADA).
It’s also cost-effective. For most U.S. communities, every $1 spent on water fluoridation saves $38 in dental treatment costs, according to the ADA.
Another benefit of fluoridated water is that it reaches everyone, even people who can’t afford a dentist or don’t routinely brush or floss, says Athanasios Zavras, DDS, DMedSc, a dentist, professor, and the chair of public health and community service at the Tufts University School of Dental Medicine in Boston.
He adds that the prevalence of ultra-processed foods and sugary drinks in the American diet significantly increases the risk of tooth decay, and supports the continued use of fluoridated water as a tool to prevent cavities.
In addition to the CDC and the ADA, organizations such as the World Health Organization (WHO), the American Medical Association (AMA), and the American Academy of Pediatrics (AAP) recommend community water fluoridation to prevent cavities.
There are two established risks associated with long-term exposure to high levels of fluoride in drinking water, according to WHO: tooth fluorosis and skeletal fluorosis.
Tooth fluorosis is damage to the enamel that coats teeth. This condition develops as teeth are growing and occurs only in children, according to WHO. It’s often a mild cosmetic issue, causing discoloration and indentations, but in more severe cases the condition can require crowns or veneers.
Skeletal fluorosis is damage to the muscles and bones in adults after years of overexposure to fluoride, according to WHO. It can initially cause joint pain, but can eventually lead to crippling damage to bones, muscles, and joints.
But the risk of skeletal fluorosis begins at concentrations more than double what’s recommended for drinking water in the United States, the WHO notes.
“Research shows that when the levels of fluoride are optimal, there are no known risks,” Dr. Zavras says. This is the case in most parts of the United States, where water naturally contains very little fluoride, Zavras notes.
“For Americans living in parts of the country where the fluoride in nature — in the soil and in the water — is highly elevated, the risk of dental or skeletal fluorosis is high,” Zavras says. “In these communities, public health officials should [and generally do] remove fluoride from drinking water supplies to bring it down to optimal levels.”
This risk is generally limited to people who drink well water. More than 28 million people who get their drinking water from wells have water with fluoride concentrations below the 0.7 mg/L level recommended for U.S. drinking water, according to the U.S. Geological Survey (USGS). Roughly 700,000 people have well water with fluoride levels of at least 2 mg/L.
A research review by WHO found that about 0.2 percent of the U.S. population is exposed to drinking water with fluoride levels above 2 mg/L.
While not definitive, some emerging research suggests that prenatal exposure to fluoride in drinking water may be linked to cognitive and neurological problems, says Ashley Malin, PhD, an assistant professor of epidemiology at the University of Florida in Gainesville.
“Studies have shown that chronic low-level prenatal fluoride exposure is associated with poorer neurodevelopmental outcomes including lower IQ, increased symptoms of ADHD, poorer executive function, and more symptoms of neurobehavioral problems,” Dr. Malin says.
One study of 229 mother-child pairs in Los Angeles, for example, found that higher prenatal fluoride exposure was associated with an increased risk of emotional, cognitive, and behavioral problems by the time the child was 3 years old. One limitation of the research is that it looked at total fluoride exposure based on lab tests of the mothers’ urine, rather than the amount of fluoride added to drinking water.
Another study of 512 mother-child pairs in Canadian cities found that kids with prenatal exposure to fluoridated drinking water had lower IQ scores at 3 to 4 years old than children of the same age from mothers living in an area without fluoridated drinking water. This study, too, estimated exposure based on lab tests of mothers’ urine in addition to data on consumption of water and other beverages that might contain fluoride.
Earlier in 2024, a federal court in California ordered the U.S. Environmental Protection Agency (EPA) to take action to respond to concerns that fluoride might lower IQ in children, although the ruling didn’t say the EPA needed to halt drinking water fluoridation. In the ruling, U.S. District Court Judge Edward Chen wrote that it wasn’t possible to “conclude with certainty” that fluoridated water is harmful to public health. But he also wrote that “the severity of the hazard at issue weighs in favor of finding the risk at issue unreasonable.”
After the ruling, both the American Dental Association and the American Academy of Pediatrics issued statements of continued support for adding fluoride to drinking water, arguing there are clear benefits and insufficient evidence of risks.
Malin advises people to err on the side of caution.
“The potential health effects of chronic low-level fluoride exposure among adults are understudied,” Malin says. “However, given findings from recent studies showing that prenatal fluoride exposure is associated with poorer child neurodevelopment, it is advisable that pregnant women take steps to reduce their fluoride intake, and their baby’s fluoride intake after birth.”
Most health experts who’ve reviewed the research on these issues say the recommended levels of fluoride added to U.S. drinking water aren’t high enough to pose serious risks, says Zavras. “If the fluoride in the water is well controlled and remains at optimal levels, there should not be a reason to worry,” Zavras says.
Here’s a recap of some of the research.
Arthritis
One study of 1,128 Chinese adults found that people exposed to higher doses of fluoride in drinking water were roughly twice as likely to develop knee osteoarthritis as individuals with the lowest exposure levels.
It’s important to note that China recommends higher levels of fluoride in drinking water than in the United States does, and also has naturally high levels of fluoride in groundwater, averaging 0.9 mg/L and reaching as high as 60 mg/L, according to another study.
“These concentrations are far above the carefully regulated fluoride level of 0.7 mg/L used in U.S. drinking water,” says Marcelle Nascimento, DDS, PhD, a professor and an assistant dean of clinical research at the University at Buffalo School of Dental Medicine. “Decades of evidence support the safety of fluoridation at [U.S.] levels.”
Bone Fractures
One study of 1,413 children and adolescents in the United States found higher levels of fluoride in drinking water associated with lower bone mineral density; denser bones are stronger and more resistant to fractures.
But the results were inconclusive; researchers didn’t find any connection between bone density and fluoride levels in urine, which measures all the fluoride people are exposed to through drinking water and other sources.
A recent meta-analysis of 28 studies found that fluoride was associated with a risk of fractures, but only at levels more than double what’s recommended for U.S. drinking water.
Similarly, a report from WHO examining research to date on the fracture risk associated with fluoride in drinking water found a risk of all fractures with fluoride levels above 4.3 mg/L and a risk of hip fractures at exposure levels above 6.5 mg/L. The WHO noted in their report that these results were not statistically significant, meaning they might be due to chance. The WHO research report also notes that in some countries, including China and India, fluoride exposure from drinking water isn’t typically as high as exposure from food.
“There is no credible evidence connecting regulated fluoride in U.S. drinking water to arthritis or fractures,” Dr. Nascimento says.
Bone Cancer
A study of 2,566 patients with bone cancer and 1,650 patients with Ewing sarcoma, tumors of the bones and soft tissue, found no connection between these malignancies and fluoride levels in drinking water.
The WHO research review concluded that there is insufficient evidence to suggest that fluoride in drinking water causes bone cancer while conceding that there is relatively little data on this connection.
Thyroid Disease
A meta-analysis of 33 studies found abnormal levels of thyroid hormones, a marker of thyroid disease, but only when people were exposed to drinking water with fluoride at more than 2.0 mg/L of water — more than double the recommended amount for municipal water in the United States.
Research linking fluoride to thyroid disorders have found potential risk at levels of 3 mg to 10 mg/L — much higher than than the U.S. standard for drinking water, Nascimento says.
“At very high doses, fluoride can affect iodine metabolism, which is related to thyroid function,” Nascimento says. “However, research consistently shows that fluoride at the levels used in U.S. public water systems does not pose a risk to thyroid health. There is no credible evidence to suggest that fluoridated water at regulated levels in the United States is associated with thyroid disorders.”
Fluoride added to drinking water significantly prevents cavities in adults and children, reducing tooth decay by 25 percent.
Exposure to excess fluoride can lead to dental or skeletal problems, but only at fluoride levels that are more than double the recommended level for drinking water in the United States.
Because of the possible effects on a child’s brain health, pregnant people may choose to err on the side of caution and limit their intake of fluoridated water, as well as their child’s intake after birth.
