Community Water Fluoridation and Urinary Fluoride Concentrations in a National Sample of Pregnant Women in Canada

Abstract

Background: Fluoride exposure in pregnant women who live in regions with and without community water fluoridation has not been established.Objective: To measure urinary fluoride levels during pregnancy using urinary creatinine and specific gravity (SG) as dilution correction standards.Methods: We measured maternal urinary fluoride (MUF) concentrations in spot samples collected in each trimester of pregnancy from 1566 pregnant women living in ten Canadian cities and enrolled in the “Maternal-Infant Research on Environmental Chemicals” cohort. We calculated intraclass correlation coefficients (ICCs) to assess variability in MUF concentrations across pregnancy. We estimated associations between MUF levels, tea consumption, and water fluoride concentrations as measured by water treatment plants using regression analyses.Results: Creatinine-adjusted MUF values (M ± SD; mg/L) were almost two-times higher for pregnant women living in fluoridated regions (0.86 ± 0.34) compared with non-fluoridated regions (0.46 ± 0.50; p<0.001). MUF values had modest reproducibility (ICC = 0.41) and tended to increase over the course of pregnancy. Creatinine-adjusted MUF was positively associated with municipal water fluoride level (B=0.52, 95% CI: 0.46, 0.57), accounting for 24% of the variance after controlling for covariates. Higher MUF concentration correlated with number of cups of black (r = 0.31 to 0.32, p<0.005), but not green tea (r = 0.04 to 0.06). Urinary creatinine and SG correction methods were highly correlated (r = 0.91) and interchangeable in models examining predictors of MUF.Conclusion: Community water fluoridation is a major source of fluoride exposure for pregnant women living in Canada. Urinary dilution correction with creatinine and SG are valid and interchangeable methods for pregnant women.