A Case-Control Study of Fluoridation and Osteosarcoma

Systematic review of epidemiological and toxicological evidence on health effects of fluoride in drinking water

INTRODUCTION

Fluoride is a naturally occurring substance that is also added to drinking water, dental hygiene products, and food supplements for preventing dental caries. Concerns have been raised about several other potential health risks of fluoride.

OBJECTIVE

To conduct a robust synthesis of evidence regarding human health risks due to exposure to fluoride in drinking water, and to develop a point of departure (POD) for setting a health-based value (HBV) for fluoride in drinking water.

METHODS

A systematic review of evidence published since recent reviews of human, animal, and in vitro data was carried out. Bradford Hill considerations were used to weigh the evidence for causality. Several key studies were considered for deriving PODs.

RESULTS

The current review identified 89 human studies, 199 animal studies, and 10 major in vitro reviews. The weight of evidence on 39 health endpoints was presented. In addition to dental fluorosis, evidence was considered strong for reduction in IQ scores in children, moderate for thyroid dysfunction, weak for kidney dysfunction, and limited for sex hormone disruptions.

CONCLUSION

The current review identified moderate dental fluorosis and reduction in IQ scores in children as the most relevant endpoints for establishing an HBV for fluoride in drinking water. PODs were derived for these two endpoints, although there is still some uncertainty in the causal weight of evidence for causality for reducing IQ scores in children and considerable uncertainty in the derivation of its POD. Given our evaluation of the overall weight of evidence, moderate dental fluorosis is suggested as the key endpoint until more evidence is accumulated on possible reduction of IQ scores effects. A POD of 1.56 mg fluoride/L for moderate dental fluorosis may be preferred as a starting point for setting an HBV for fluoride in drinking water to protect against moderate and severe dental fluorosis. Although outside the scope of the current review, precautionary concerns for potential neurodevelopmental cognitive effects may warrant special consideration in the derivation of the HBV for fluoride in drinking water.

Effect of fluoridated water on dental caries and fluorosis in schoolchildren who use fluoridated dentifrice

This cross-sectional study evaluated the prevalence and severity of dental caries and fluorosis in children and adolescents using fluoridated toothpaste, from areas with and without fluoridated water. Parents of 5-year-old children and 12-year-old adolescents from neighbourhoods that are supplied with and without fluoridated water answered questionnaires for determining socio-economic and demographic characteristics and habits related to oral health. The individuals were examined, and dental caries and fluorosis were measured by dmft/DMFT and TF indexes, respectively. Descriptive, bivariate and logistic regression analyses were performed (p < 0.05). Of 692 participants, 47.7% were 5-year-olds and 52.3% were 12-year-olds. The mean dmft/DMFT in the 5-year-olds/ 12-year-olds from Exposed and Not Exposed fluoridated water groups was 1.53 (± 2.47) and 3.54 (± 4.10) / 1.53 (± 1.81) and 3.54 (± 3.82), respectively. Children (OR = 2.86, 95% CI = 1.71-4.75) and adolescents (OR = 1.95, 95% CI = 1.24-3.05), who did not consume fluoridated water, had greater caries experience. Among adolescents, there was an association between fluoridated water and the prevalence of very mild/mild fluorosis (OR = 5.45, 95% CI: 3.23-9.19) and moderate fluorosis (OR = 11.11, 95% CI = 4.43-27.87). Children and adolescents, who consumed fluoridated water, presented lower prevalence and severity of dental caries compared to those who used only fluoridated toothpaste as the source of fluoride. There is an association between water fluoridation and very mild/mild and moderate fluorosis in adolescents.

A case-control study of topical and supplemental fluoride use and osteosarcoma risk

BACKGROUND

A relationship between fluoride and osteosarcoma has been hypothesized but not validated. To the authors' knowledge, there are no published studies examining topical fluoride or dietary fluoride supplements and osteosarcoma risk. The purpose of this study was to examine the association between ever or never use of topical and dietary fluoride supplements and osteosarcoma.

METHODS

The authors performed a secondary data analysis on data from 2 separate but linked studies. Patients for Phase 1 and Phase 2 were selected from US hospitals using a hospital-based matched case-control study design. Case patients were those who had received diagnoses of osteosarcoma, and control patients were those who had received diagnoses of other bone tumors or nonneoplastic conditions. In Phase 1, case patients (N = 209) and control patients (N = 440) were those seeking treatment at orthopedic departments from 1989 through 1993. In Phase 2, incident case patients (N = 108) and control patients (N = 296) were identified and treated by physicians from 1994 through 2000. This analysis included all patients who met eligibility criteria and on whom the authors had complete data on exposure, outcome, and covariates. The authors used conditional logistic regression to estimate odds ratios and 95% confidence intervals (CIs) for the association of topical fluoride use and supplemental fluoride use with osteosarcoma.

RESULTS

The adjusted odds ratios were 0.94 (95% CI, 0.60 to 1.46) and 0.78 (95% CI, 0.46 to 1.33) for topical fluoride and supplemental fluoride, respectively.

CONCLUSIONS

Neither topical nor dietary fluoride supplements are associated with an increased risk of developing osteosarcoma.

PRACTICAL IMPLICATIONS

Supplemental and topical fluorides used in the dental office and in over-the-counter products are not related to an increased risk of developing osteosarcoma.