In response to concerns over the possible carcinogenicity of fluoride compounds added to drinking water raised by the results of a recent animal experiment, we evaluated 36 years of US.cancer mortality data and 15 years of cancer incidence data from two population-based cancer registries, in relation to the fluoridation status of drinking water supplies in the populations under study. Osteosarcomas of the bone were singled out for detailed analysis based on the results of the animal experiment. Among both males and females residing in counties having undergone rapid fluoridation, the relative risk of death from cancers of the bones and joints was the same after 20-35 years of fluoridation as it was in the years immediately preceding fluoridation. A similar lack of a relationship to timing of fluoridation was noted for the incidence of bone and joint cancers, and osteosarcomas. The relative risk of developing these cancers 20 or more years after fluoridation was lower than the risk associated with less than five years of fluoridation among both males and females. The mortality and incidence data in this survey allowed an evaluation of the patterns of risk for virtually all forms of cancer in relation to the timing of fluoridation of drinking water supplies. For no type of malignancy was there consistent evidence of a relationship with the patterns of fluoridation. One site, renal cancer, showed a suggestive relationship between incidence rates and duration of fluoridation in the aggregate data from the registries. However, no such trends were seen when incidence data were examined for two separate periods, and the mortality data for renal cancer actually yielded some evidence of an inverse relationship with duration of fluoridation.
Thus, in a study of over 2,300,000 cancer deaths in fluoridated counties across the United States, and over 125,000 incident cancer cases in fluoridated counties covered by two population-based cancer registries, we identified no trends in cancer risk that could be ascribed to the consumption of fluoridated drinking water.
FLUORIDATION OF DRINKING WATER AND SUBSEQUENT CANCER INCIDENCE AND MORTALITY Robert N. Hoover, M.D., Sc.D., Susan S, Devesa, Ph.D., Kenneth P. Cantor, Ph.D., Jay H. Lubin, Ph.D., and Joseph F. Fraumeni, Jr., M.D. From: Epidemiology and Biostatistics Program, Division of Cancer Etiology, National Cancer Institute, National Institutes of Health, Bethesda, Maryland