It is well known that fluoride provides important public health benefits by effectively preventing dental caries in children. The Public Health Service (1991) endorses artificial fluoridation of drinking water at a concentration of 0.7-1.2 milligrams of fluoride per liter of water (or parts per million) as the optimally beneficial level for preventing dental caries. The U.S. Environmental Protection Agency (USEPA) allows up to 2 parts per million for artificial fluoridation and up to 4 parts per million for naturally occurring fluoride (National Primary Drinking Water Regulations, 40 CFR 141.11 and 143.3). Other potential sources of fluoride ingestion include food, vitamins, and swallowed toothpaste.
Recently, a national study of drinking water fluoridation at the county level found a significant association with osteosarcoma incidence among males under 20 years of age (Hoover et at 1991). However, the meaning of the association was questioned by the authors because of the absence of a linear trend of association with the duration of time for which the water supplies were fluoridated. Furthermore, the simple study design used did not have individual information on the average amount of water ingested daily, use of dental fluoride supplements, long term residence, other potentially confounding (or causal) exposures, or genetic involvement.
As a follow-up to the study by Hoover et at, a small study of similar design was initiated by the New Jersey Department of Health to compare drinking water fluoridation at the municipal level with the municipal residence of osteosarcoma cases at the time of diagnosis. No interviews were conducted and data on individual residential history, average amount of water ingested, use of dental fluoride supplements, exposure to other carcinogens and familial cancer history were not available. In addition, the total number of cases was small. Therefore, observations should be interpreted cautiously because: 1) exposure misclassification could lead to under- or overestimation of effects, 2) unmeasured confounding by other potential causes of osteosarcomas could introduce bias leading to under- or overestimation of effects of exposure, and 3) an observed association could be due to chance.
Osteosarcoma incidence between 1979 and 1987 was compared by ecologic epidemiology methods to water supply fluoridation in seven counties in central New Jersey. Twelve cases were diagnosed among males under age 20 in fluoridated municipalities vs eight cases in non-fluoridated municipalities. The rate ratio of incidence in fluoridated vs non-fluoridated municipalities was 3.4 with a 95% statistical confidence interval (95%Cl) between 1.8 and 6.0. All twelve cases in fluoridated municipalities resided in a three county area with the greatest prevalence of fluoridation. The rate ratio of incidence in fluoridated vs non-fluoridated municipalities in the three county area was 5.1 (95%CI 2.7-9.0). Among 10-19 year old males in those three counties, the rate ratio was 6.9 (95%Cl 3.3-13). No other age/sex groups exhibited significant association with fluoridation.
Because of the limitations of the study design and the small numbers of cases that occurred, this analysis does not imply a causal connection between fluoridation and osteosarcoma. From the public health perspective, the findings are not sufficient to recommend that fluoridation of water supplies be halted, but do support the importance of investigating the possible link between osteosarcoma and overall ingestion of fluoride, In addition, it is recommended that dentists identify whether children reside in fluoridated communities and appropriately advise on fluoride supplementation.