Associations between Urinary, Dietary, and Water Fluoride Concentrations among Children in Mexico and Canada
Department of Psychology, York University, Toronto, ON M3J 1P3, Canada
Departamento de Salud, Universidad Iberoamericana, Ciudad de México 01219, Mexico
Faculty of Health Sciences, Simon Fraser University, Vancouver, BC V5A 1S6, Canada
School of Dentistry, Indiana University, Indianapolis, IN 46202, USA
Department of Social and Preventive Medicine, Laval University, Quebec City, QC G1V 0A6, Canada
Environmental Medicine and Public Health, Icahn School of Medicine at Mount Sinai, New York, NY 10029, USA
School of Public Health, Instituto Nacional de Salud Pública, Cuernavaca 62100, Mexico
Author to whom correspondence should be addressed.
Toxics 2020, 8(4), 110; https://doi.org/10.3390/toxics8040110
Received: 25 September 2020 / Revised: 29 October 2020 / Accepted: 30 October 2020 / Published: 20 November 2020
(This article belongs to the Section Toxicology)
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 645 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 (t = 4.26, p < 0.001) in PROGRESS: 0.74 (0.42) and fluoridated Canadian communities: 0.66 (0.47), but lower in non-fluoridated Canadian communities: 0.42 (0.31) (t = −6.37, p < 0.001). Water fluoride concentrations were significantly associated with CUF after covariate adjustment for age and sex in MIREC (B = 0.44, 95% CI: 0.30, 0.59, p < 0.001). 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.