Urinary fluoride patterns among children in Mexico and Canada

Abstract

Background: New research suggesting fluoride is a developmental neurotoxicant highlights the importance of characterizing fluoride exposure in children. Fluoride is added to salt in Mexico and to drinking water in Canada to prevent dental caries. We examined the association of childhood urinary fluoride (CUF) with food and water fluoride levels in Mexico and Canada, respectively. Methods: We included 551 children (ages 4-6) from the Programming Research in Obesity, Growth, Environment and Social Stress (PROGRESS) cohort in Mexico City, and 522 children (ages 2-6) from the Maternal-Infant Research on Environmental Chemicals (MIREC) cohort in Canada. We applied Spearman correlations, T-tests or covariate adjusted linear regression to examine associations of CUF (mg/L; adjusted for specific gravity) with demographics and food or water fluoride concentrations. We used equivalence testing to compare cohort means. Results: Median (IQR) CUF concentrations were 0.67 (0.36) in PROGRESS, 0.56 (0.76) in fluoridated Canadian communities, and 0.35 (0.53) in non-fluoridated Canadian communities. 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≤.001). CUF tended to increase with age in PROGRESS (ρ=.10, p=.02) and MIREC (ρ=.17, p≤.001). In MIREC, CUF was higher in males (0.79+/-0.74) than females (0.54+/-0.58, p<.001); however, no sex differences were observed in PROGRESS (p=.97). In MIREC, water fluoride concentrations (median=0.2 mg/L) were significantly associated with CUF after covariate adjustment for age and sex (B=0.36, 95%CI: 0.11, 0.61, p=.005). Daily food and beverage fluoride intake (median=624.41 mcg/day) was not associated with CUF in PROGRESS (p=.89). Conclusion: Our findings suggest that the magnitude of fluoride exposure is comparable among children in Mexico City and fluoridated Canadian communities, despite different sources of exposure. Further studies are needed to clarify whether higher CUF among older children reflects different exposure patterns, sources of exposure or age-related toxicokinetics. Keywords: Fluoride, exposure, intake, development, epidemiology.