The National Cancer Institute assembled a fact sheet about fluoride and fluoridated water.

The data on the safety of fluoridated water is mixed and conflicting.

A possible relationship between fluoridated water and cancer risk has been debated for years. The debate resurfaced in 1990 when a 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, other studies in humans and in animals have not shown an association between fluoridated water and cancer (5–7).

In a February 1991 Public Health Service (PHS) report, the agency said it found no evidence of an association between fluoride and cancer in humans. But in 2011, the U.S. Department of Health and Human Services proposed that the nation’s water utilities sharply reduce the amount of fluoride in tap water, to protect Americans, especially children, from tooth and bone damage caused by overexposure to this chemical.

Dentists have found that applying fluoride to tooth enamel is effective in preventing tooth decay. But people overexposed to fluoride can suffer tooth, joint and bone damage. Scientists have associated high fluoride consumption with reproductive and developmental system damage, neurotoxicity, hormonal disruption and bone cancer.