Fluoride, which may be toxic to the developing brain, is added to salt in Mexico and drinking water in Canada to prevent dental caries. We compared childhood urinary fluoride (CUF) concentrations in Mexico City and Canada to characterize patterns of fluoride exposure in these two populations. We also examined associations of CUF with dietary and water fluoride levels in Mexico City and Canada respectively. We included 561 children (ages 4-6; mean age 4.8 years) from the Programming Research in Obesity, Growth, Environment, and Social Stress (PROGRESS) cohort in Mexico City, and 626 children (ages 2-6; mean age 3.7 years) from the Maternal-Infant Research on Environmental Chemicals (MIREC) cohort in Canada. We applied Spearman correlations, T-tests, ANOVA or covariate-adjusted linear regression to examine associations of CUF (mg/L; adjusted for specific gravity) with demographics and dietary or water fluoride concentrations. We used Welch equivalence testing to compare means across cohorts. Mean (SD) CUF was equivalent in PROGRESS: 0.74 (0.42) and fluoridated Canadian communities: 0.79 (0.71), but lower in non-fluoridated Canadian communities: 0.55 (0.60), t (276) = -6.02, p < 0.001). In MIREC, mean (SD) CUF was higher in males: 0.79 (0.74) than females: 0.54 (0.58), p < 0.001; no sex differences were observed in PROGRESS (p = 0.97). Water fluoride concentrations were significantly associated with CUF after covariate adjustment for age and sex in MIREC (B = 0.36, 95% CI: 0.11, 0.61, p = 0.005). In contrast, daily food and beverage fluoride intake was not associated with CUF in PROGRESS (p = 0.82). We found that CUF levels are comparable among children in Mexico City and fluoridated Canadian communities, despite distinct sources of exposure. Community water fluoridation is a major source of fluoride exposure for Canadian children. Further studies are needed to clarify whether higher CUF in older children reflects different exposure patterns, sources of exposure, or age-related toxicokinetics.
Authors: Rivka Green, Christine Till, Alejandra Cantoral, Bruce Lanphear, E Angeles Martinez-Mier, Pierre Ayotte, Robert O Wright, Martha M Tellez-Rojo, Ashley J Malin
; Full Source: Toxics 2020 Nov 20;8(4):E110. doi: 10.3390/toxics8040110.