Fluoridated Water
What is fluoride, and where is it found?
Fluoride is the name given to a group of compounds that are composed of the naturally occurring element fluorine and one or more other elements. Fluorides are present naturally in water and soil at varying levels.
In the 1940s, scientists discovered that people who lived where drinking water supplies had naturally occurring fluoride levels of approximately 1 part fluoride per million parts water or greater (≥1.0 ppm) had fewer dental caries (cavities) than people who lived where fluoride levels in drinking water were lower. Many more recent studies have supported this finding (1).
It was subsequently found that fluoride can prevent and even reverse tooth decay by inhibiting bacteria that produce acid in the mouth and by enhancing remineralization, the process through which tooth enamel is “rebuilt” after it begins to decay (1,2).
In addition to building up in teeth, ingested fluoride accumulates in bones.
What is water fluoridation?
Water fluoridation is the process of adding fluoride to the water supply. The current recommendation for the level of fluoridation is 0.7 ppm, or 0.7 milligrams of fluoride per liter of water, which has been determined to prevent tooth decay without discoloring the teeth (3). The Centers for Disease Control and Prevention (CDC) has information and guidelines on community water fluoridation in the United States.
When did water fluoridation begin in the United States, and how common is it?
In 1945, the city of Grand Rapids, Michigan, adjusted the fluoride content of its water supply to 1.0 ppm and thus became the first U.S. city to implement community water fluoridation. In 2022, more than 72% of the U.S. population served by public water systems, and more than 62% of the U.S. population overall, had access to fluoridated water.
Can fluoridated water cause cancer?
A 1991 study by the National Toxicology Program, part of the National Institute of Environmental Health Sciences, showed an increased number of osteosarcomas (bone tumors) in male rats given water high in fluoride for 2 years (4). However, two major comprehensive reviews of studies in both humans and animals published around the same time concluded that there was no association between fluoridated water and cancer (5,6).
In one of these comprehensive reviews, published in 1991, the Public Health Service (PHS) concluded, based on a review of more than 50 human epidemiologic studies conducted in the previous 40 years, that optimal fluoridation of drinking water “does not pose a detectable cancer risk to humans,” as evidenced by extensive human epidemiologic data (5).
For example, in one of the studies reviewed by the PHS, scientists at NCI evaluated the relationships between water fluoridation and both the number of cancer deaths in the United States during a 36-year period and the number of new cancer cases during a 15-year period. After examining more than 2.2 million cancer death records and 125,000 cancer case records in counties using fluoridated water, the researchers found no indication of increased cancer risk in people who consumed fluoridated drinking water (5).
In the second comprehensive review, published in 1993, the Subcommittee on Health Effects of Ingested Fluoride of the National Research Council, part of the National Academy of Sciences, conducted an extensive literature review of studies on the possible association between fluoridated drinking water and cancer risk. The review included not only the data from the more than 50 human epidemiologic studies that the PHS had reviewed, but also results from six animal studies. The Subcommittee concluded that none of the data demonstrated an association between fluoridated drinking water and cancer (6). A 1999 report by the CDC supported these findings, concluding that studies to date have produced “no credible evidence” of an association between fluoridated drinking water and an increased risk for cancer (2).
Since those extensive reviews, several additional epidemiologic studies have been conducted, with no credible evidence of an association between fluoride levels and osteosarcoma or Ewing sarcoma (7–12). Most studies relied on historical estimates of exposure. However, in 2011, researchers examined the possible relationship between fluoride exposure and osteosarcoma in a new way: they measured fluoride concentration in samples of normal bone that were adjacent to a person’s tumor. Because fluoride naturally accumulates in bone, this method provides a more accurate measure of cumulative fluoride exposure than relying on the memory of study participants or municipal water treatment records. The analysis showed no difference in bone fluoride levels between people with osteosarcoma and people in a control group who had other malignant bone tumors (7).