Associations between Urinary, Dietary, and Water Fluoride Concentrations among Children in Mexico and Canada.

Rivka Green,E Martinez-Mier,Alejandra Cantoral,Bruce Lanphear,Robert Wright,Martha Tellez-Rojo,Pierre Ayotte,Ashley Malin,Christine Till

doi:10.3390/toxics8040110

Abstract

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.

Highlights

Fluoride is often added to water, salt, or milk to prevent dental cavities [1]
Water fluoride concentrations were significantly associated with childhood urinary fluoride (CUF) after covariate adjustment for age and sex in Maternal–Infant Research on Environmental Chemicals (MIREC) (B = 0.44, 95% CI: 0.30, 0.59, p < 0.001)
MIREC: The Maternal–Infant Research on Environmental Chemicals (MIREC) study is a large sample of pregnant women and children that were recruited from ten cities across Canada from

Summary

Introduction

Fluoride is often added to water, salt, or milk to prevent dental cavities [1]. Approximately 39%of Canadians and 73% of Americans on public water distribution systems have fluoride added to drinking water to achieve the optimal concentration of 0.7 mg/L for dental carries prevention [2,3].Toxics 2020, 8, 110; doi:10.3390/toxics8040110 www.mdpi.com/journal/toxicsIn the United States (US), fluoridated water is the main source of fluoride exposure, accounting for approximately 60% of total daily fluoride intake among adults, and 42% of total daily fluoride intake among children under the age of 12 [4]. Fluoride is often added to water, salt, or milk to prevent dental cavities [1]. Of Canadians and 73% of Americans on public water distribution systems have fluoride added to drinking water to achieve the optimal concentration of 0.7 mg/L for dental carries prevention [2,3]. In Mexico, sodium fluoride or potassium fluoride are added to salt at 250 ± 50 mg/L in regions where naturally occurring fluoride in water is less than. Urinary fluoride levels typically approximate the concentration of fluoride found in tap water in adults [9,13,14] and children [15,16]. In Mexico, salt fluoride intake patterns or contributions of salt fluoride to urinary fluoride levels are not well-established [17]

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