Fluoride exposure via public drinking water supplies and associated health outcomes: an ecological study in England

Abstract

BACKGROUND AND AIM The protective effect of drinking water fluoridation on dental caries is established. While adverse effects are known for fluoride concentrations above 1.5mg/L, the evidence is less clear for effects at lower concentrations. In new updated analyses, we aimed to estimate the association between fluoride exposure and dental health outcomes and hip fractures. METHODS Exposure was defined as mean public drinking water fluoride concentrations, assigned to geographical areas, over time periods of interest. Concentrations were categorised: <0.1, 0.1-<0.2, 0.2-<0.4, 0.4-<0.7, ≥0.7mg/L. Area-level health outcomes, deprivation scores, and age- and sex-specific denominators were obtained from hospital data, oral health surveys, and routine data sources. Binomial models with logit link were used to determine the association (adjusted odds ratios) between fluoride and dental caries prevalence. Negative binomial models were used to determine the association (adjusted incidence rate ratios) with dental extractions and hip fractures. RESULTS The association between fluoride and dental outcomes varied by deprivation. Odds of caries decreased in each fluoride concentration category relative to the lowest, with the greatest reduction in the most deprived quintile (ORs 0.61-0.80, composite p<0.001). Incidence of hospital admissions for carious tooth extractions decreased similarly (IRRs 0.37-0.66, composite p<0.001). The association with hip fracture varied by age (p<0.001), with evidence of a protective association in those aged under 50 (IRRs 0.83-0.97, composite p<0.001) and an adverse association in those aged over 80 (IRRs 0.98-1.08, composite p<0.01) at some individual concentration categories. There was no evidence of a dose response. CONCLUSION Exposure to fluoride in drinking water, at concentrations <1.5mg/L, was associated with reduced dental caries and extractions. The most deprived populations benefited the most. There was no clear evidence of an association with hip fractures. The findings support adoption of water fluoridation as an equitable dental public health intervention. KEYWORDS Fluoride; oral health; fractures