The short answer
Fluoride is added to many public water supplies to prevent tooth decay, and a long-running claim says it causes cancer, especially a rare bone cancer called osteosarcoma. Large reviews of human studies have not found convincing evidence that water fluoridation causes cancer, including the biggest studies of osteosarcoma. Research continues, but the current evidence is reassuring.
Fluoride is added to water to prevent tooth decay.
The main cancer concern raised is a rare bone cancer, osteosarcoma.
Large reviews of human studies have not found convincing evidence of a cancer link.
The biggest osteosarcoma studies found no association with fluoride levels.
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The full explanation.
The claim
Water fluoridation — adding small amounts of fluoride to public water to reduce tooth decay — has long drawn claims that it causes cancer, most often a rare bone cancer called osteosarcoma. The debate has resurfaced in recent policy discussions.
What the evidence shows
The National Cancer Institute reports that many studies in people have looked at whether fluoridated water is linked to cancer, and reviews of that research have not found convincing evidence of a link. Concern was originally fueled partly by a 1990s study in which rats given very high fluoride levels had more bone tumors, but comprehensive reviews of human and animal data did not find a matching risk in people.
The osteosarcoma question
Osteosarcoma has received the most study because it is a bone cancer and fluoride collects in bone. The largest studies, including a large British analysis of thousands of cases, found no link between the level of fluoride in drinking water and the rate of osteosarcoma. Authorities describe the evidence as not showing a detectable cancer risk at the levels used to fluoridate water.
The bottom line
Based on large reviews of human studies, fluoride in drinking water at the levels used for dental health is not established to cause cancer, including osteosarcoma. As with many exposures, scientists keep studying the question, but the current evidence is reassuring.
Words to know
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Common questions
▸Does fluoride in water cause cancer?
Large reviews of human studies have not found convincing evidence that water fluoridation causes cancer.
▸What about bone cancer specifically?
The biggest studies of osteosarcoma found no link between fluoride levels in drinking water and this rare bone cancer.
▸Where did the concern come from?
Partly from a study of rats given very high fluoride; comprehensive reviews of human data did not find a matching risk in people.
▸Is the science settled?
Scientists keep studying the question, but the current evidence at fluoridation levels is reassuring.
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Your next step
What the evidence shows about common cancer claims.
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