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

BACKGROUND: Fluoride exposures have not been established for pregnant women who live in regions with and without community water fluoridation. OBJECTIVE: Our aim was to measure urinary fluoride levels during pregnancy. We also assessed the contribution of drinking-water and tea consumption habits to maternal urinary fluoride (MUF) concentrations and evaluated the impact of various dilution correction standards, including adjustment for urinary creatinine and specific gravity (SG). METHODS: We measured MUF concentrations in spot samples collected in each trimester of pregnancy from 1,566 pregnant women in the Maternal Infant Research on Environmental Chemicals cohort. We calculated intraclass correlation coefficients (ICCs) to assess variability in :MIT concentrations across pregnancy. We used regression analyses to estimate associations between MUF levels, tea consumption, and water fluoride concentrations as measured by water treatment plants. RESULTS: Creatinine-adjusted MAT values (mean SD; milligrams per liter) were almost two times higher for pregnant women living in fluoridated regions (0.87 +/- 0.50) compared with nonlluoridated regions (0.46 +/- 0.34; p<0.001). MUF values tended to increase over the course of pregnancy using both unadjusted values and adjusted values. Reproducibility of the unadjusted and adjusted MUF values was modest (ICC range = 0.37-0.40). The municipal water fluoride level was positively associated with creatinine-adjusted MUF (B = 0.52, 95% CI: 0.46, 0.57), accounting for 24% of the variance after controlling for covariates. Higher MUF concentrations correlated with numbers of cups of black (r=0.31-0.32 but not green tea = 0.04-0.06). Urinary creatinine and SG correction methods were highly correlated (r = 0.91) and were 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 were shown to be interchangeable for our sample of pregnant women.