Background: Because osteosarcomas may develop in rats exposed to fluoridated water, water fluoridation might pose a cancer risk to humans.
Methods: A time trend analysis of the cumulative risk (CR) of bone cancer for the period 1958-1987 for 40 cancer registry areas showed an increased risk for young males in Canada, Europe, and the United States, and a decreased lifetime risk for either sex in Europe.
Results: This was unrelated to water fluoridation and may have resulted from changes in coding practices. Bone cancer risk was inversely related to the incidence of cancers of unknown origin, suggesting that bone metastases were erroneously coded as primary bone cancer. In 1968-1972, most areas recorded more bone cancer deaths than new cases of the disease.
Conclusions: The mortality/incidence ratio, but not the incidence rate (IR), has dropped sharply since then, which erodes the basis of past inferences relating cancer mortality to fluoridation.