Adding Fluoride to Water, Is it Safe and Effective?
How water fluoridation began
The history of water fluoridation begins in the early 20th century, when a young dentist named Dr. Frederick McKay noticed a strange phenomenon in Colorado Springs. Residents of the town had distinctive brown, mottled stains on their teeth. Further observation revealed that, despite these notable stains, people with the “Colorado brown stain” seemed to have teeth that were unusually resistant to decay. Tooth decay, also called caries or cavities, causes holes to form in teeth.
Researchers traced the cause of the stain to the town’s water supply, which contained abnormally high levels of fluoride. This finding prompted dentists to investigate whether it was possible to reap the beneficial, tooth-protecting effects of fluoridated water without experiencing the downsides of staining your teeth.
In 1945, Grand Rapids, Michigan, became the first city in the world to approve a pilot water fluoridation program. Researchers added a small amount of fluoride to the city’s water supply and measured rates of tooth decay in the town’s nearly 30,000 schoolchildren over the next decade. Their findings revealed that children who were born after water fluoridation began had more than 60% fewer cavities than those born prior to the program.
The benefits of fluoridated water
Since 1945, water fluoridation has proliferated as a widespread public health practice around the world, and organizations such as the American Dental Association (ADA) stand firmly in support of water fluoridation. Many studies support the notion that water fluoridation prevents cavities in children.
Although fluoridated toothpaste has many of the same tooth-protecting properties of fluoridated water, experts say the latter comes with certain public health benefits that toothpaste lacks. That’s because ingesting fluoride, rather than brushing with it, leads to more constant levels of fluoride in the mouth throughout the day, which is especially beneficial for children with developing teeth. Fluoridated water also provides a baseline level of protection for lower-income people who may not have consistent access to fluoridated toothpaste or to other forms of dental care.
That was true in decades past — but some recent research is raising the question of how helpful fluoridated water is for cavity prevention.
A review of over 150 studies showed that, in recent years, water fluoridation may not be as effective at preventing cavities as it was in the 1970s, after fluoridated toothpaste became more widespread. This change may be because fluoridated toothpaste is providing enough benefit that fluoridated water no longer makes as dramatic of a difference.
However, it’s important to note that the review did not include any studies from low-income countries, where fluoridated toothpaste may be less readily available. The review also notes that challenges in measuring the effects of fluoridation programs make their potential benefits difficult to quantify over time.
Is fluoridated water safe?
Both the U.S. Centers for Disease Control and Prevention (CDC) and the ADA maintain that at the levels found in the public water supply — about 0.7 mg per liter — fluoride is beneficial to public dental health and carries few documented risks.
Still, fluoride has been the focus of much safety research, and the topic continues to be a matter of public interest and controversy.
Consuming even higher levels of fluoride over a long period of time can also lead to a condition called skeletal fluorosis, which compromises the integrity of the bones. This is because excessive deposits of fluoride in the skeleton causes the bones to become hard and brittle, making them more susceptible to fractures.
Both dental fluorosis and skeletal fluorosis generally occur in regions with abnormally high levels of natural fluoride deposits that leach into the water supply. Because skeletal fluorosis requires extremely high levels of fluoride exposure, it’s mostly observed in regions with fluoride-contaminated groundwater, but dental fluorosis can occur due to low-level fluoride exposure through artificially fluoridated water.
Initial concerns about fluoridated water focused on whether it could cause cancer. This belief stemmed from the theory that fluoride build-up in the growth plate of the bones could lead to osteosarcoma, a type of bone cancer. While this connection is difficult to evaluate in humans, most studies have not found any strong evidence for such a link.
More recently, concerns have been raised about the potential neurotoxic effects of fluoride. A 2024 review by the U.S. National Toxicology Program found that high levels of fluoride exposure were associated with lower IQ in children. However, the levels of fluoride exposure associated with IQ changes were roughly double the levels of fluoride found in water supplies of countries like the U.S. or the U.K. — about 1.5 mg per liter. The authors also note that while fluoride levels are correlated with cognitive differences in children, their results do not show that fluoride causes cognitive changes.
Collectively, these results point toward a common saying in toxicology: “The dose makes the poison.” In other words, a substance can be safe in small amounts, but harmful in larger quantities. For example, eating a tablespoon of soy sauce is perfectly safe, but consuming an entire bottle can cause seizures.